International Meteorological Institute in Stockholm Department of Meteorology, Stockholm University

INTERNATIONAL METEOROLOGICAL INSTITUTE IN STOCKHOLM DEPARTMENT OF METEOROLOGY, STOCKHOLM UNIVERSITY

BIENNIAL REPORT 2011–2012

FRONT COVER

Wave activity in the middle atmosphere leads to coupling processes on a global scale. A prominent example is the dynamic control of the summer mesosphere by the lower atmosphere in both hemispheres. These coupling processes are studied by means of global satellite observations and numerical modelling. A visible indicator of the wave-driven circulation in the mesosphere are noctilucent clouds (NLC) that occur in the high-latitude summer. Here large-scale updraft leads to extreme adiabatic cooling and mesopause temperatures down to 100 K. For details, see the research article on "Global dynamical coupling in the middle atmosphere" in this biennial report.

INTERNATIONAL METEOROLOGICAL INSTITUTE IN STOCKHOLM (IMI) AND DEPARTMENT OF METEOROLOGY, STOCKHOLM UNIVERSITY (MISU)

BIENNIAL REPORT 1 JANUARY 2011– 31 DECEMBER 2012

Postal address Department of Meteorology Stockholm University S-106 91 Stockholm, Sweden

Telephone Int. +46-8-16 23 95 Nat. 08-16 23 95

Telefax Int. +46-8-15 71 85 Nat. 08-15 71 85

E-mail [email protected]

Internet www.misu.su.se

ISSN 0349-0068 Printed at US-AB (PrintCenter), Stockholm University 2013

TABLE OF CONTENTS

THE INTERNATIONAL METEOROLOGICAL INSTITUTE IN STOCKHOLM ...... 8 GOVERNING BOARD ...... 8 DIRECTOR...... 8 TELLUS ...... 9

THE DEPARTMENT OF METEOROLOGY AT STOCKHOLM UNIVERSITY ...... 10 HEAD OF THE DEPARTMENT ...... 10

INTRODUCTION ...... 12

RESEARCH ACTIVITIES ...... 16 Research groups ...... 16 ATMOSPHERIC PHYSICS ...... 16 CHEMICAL METEOROLOGY ...... 17 DYNAMIC METEOROLOGY ...... 17 PHYSICAL OCEANOGRAPHY ...... 18 How IMI shaped my scientific life by Jost Heintzenberg ...... 19 Fond memories from Stockholm by Raymond Pierrehumbert ...... 21 Global dynamical coupling in the middle atmosphere...... 23 Climate modeling as a scientific tool to understand our climate and climate change ...... 28 Why does the Atlantic Ocean form the northern hemisphere deep water? ...... 31 Arctic climate change ...... 35 List of publications ...... 42 2009 ...... 42 2010 ...... 45 2011 ...... 47 2012 ...... 52 2013 ...... 56

STAFF MEMBERS (AS OF DECEMBER 2012) ...... 61

VISITORS ...... 64

FINANCES ...... 71

PhD THESES 2009-2012 ...... 75

ACRONYMS ...... 78

THE INSTITUTE

BIENNIAL REPORT 2011 – 2012 7

THE INSTITUTE

THE INTERNATIONAL METEOROLOGICAL INSTITUTE IN STOCKHOLM The International Meteorological Institute in Stockholm (IMI) was created in 1955 by a decision of the Swedish Parliament with the objective "to conduct research in meteorology and associated fields and to promote international scientific co-operation within meteorology". This decision was a result of initiatives taken by Professor Carl-Gustaf Rossby, strongly supported by the former Minister for Foreign Affairs of Sweden, Richard Sandler.

The most important function of the institute is to provide opportunities for foreign scientists to work in Sweden for varying periods of time in close collaboration with their Swedish colleagues. The institute also publishes the scientific journal Tellus.

The institute was an independent institute financed by a direct contribution from the Swedish Government until the end of 2009. Since 1 January 2010, IMI is an independent institute at the Department of Meteor- ology, of which it is an integral part, funded by Stockholm University through the Faculty of Science.

GOVERNING BOARD Anders Karlqvist, Professor of System Analysis, Appointed by Stockholm University. Joakim Langner, Research Director at the Swedish Meteorological and Hydrological Institute. Appointed by SMHI. Until 14 February 2011. Pontus Matstoms, Research Director at the Swedish Meteorological and Hydrological Institute. Ap- pointed by SMHI. From 15 February 2011. Per Holmlund, Professor of Glaciology, Stockholm University. Appointed by Stockholm University. Erland Källén, Professor of Dynamic Meteorology, Stockholm University. Appointed by the Board. Caroline Leck, Professor in Chemical Meteorology. Appointed by the Board. Anna Rutgersson, Professor in Meterology. Appointed by the Royal Swedish Academy of Sciences. Michael Tjernström, Director of the Institute. Ex Officio Member. Until 31 July 2012. Jonas Nycander, (Deputy) Director of the Institute. Ex Officio Member. Rodrigo Cabellero, Deputy director of the Institute. Ex Officio Member. From 1 August 2012 Secretary of the Board: Albert de Haan, Economist.

DIRECTOR Until 2012-07-31

Michael Tjernström, Professor of Boundary-Layer Meteorology.

From 2012-08-01

Jonas Nycander, Professor of Geophysical Fluid Dynamics.

Deputy Director, Rodrigo Cabellero, Professor in Climate Modelling.

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THE INSTITUTE

TELLUS The international scientific journal Tellus was founded in 1949. It started as a quarterly geophysical journal published by the Swedish Geophysical Society and with professor Carl-Gustaf Rossby as Editor-in- Chief. The Swedish publisher Almqvist & Wiksell handled printing and subscriptions to the journal. Since the very beginning it was the aim of Rossby to publish in Tellus both original research articles, review articles and book reviews in all geophysical sciences. During the first 15 years almost every field in geophysics was represented in Tellus. Carl-Gustaf Rossby died in 1957 and Bert Bolin became Editor- in-Chief for the journal.

The number of submissions increased, and in 1969 Tellus became a bi-monthly journal. Since the 1960’s there was a shift of emphasis towards meteorology, atmospheric physics, atmospheric chemistry, oceanography and general fluid mechanics. The trend continued, and since the 1970’s no articles in other areas were published in Tellus.

In 1975 a new publisher, Munksgaard in Copenhagen, Denmark was contracted. Munksgaard was owned by Blackwell Publishing, which later was taken over by Wiley.

It gradually became obvious that all articles in the areas of meteorology, atmospheric chemistry, dynamic meteorology etc. were not of sufficient interest to all readers of the journal, and therefore it was decided to establish two parallel series of Tellus from 1 January 1983. These two series are: Tellus A. Dynamic meteorology and oceanography and Tellus B. Atmospheric physics and atmospheric chemistry .

The 6 annual issues increased to 10 divided into 5 issues for each series appearing alternately every month except June and December. Bert Bolin continued to serve as Editor-in-Chief for Tellus A, and Henning Rodhe became Editor-in-Chief for Tellus B.

As of 1 January 2007 the ownership of Tellus was transferred from the Swedish Geophysical Society to the International Meteorological Institute in Stockholm (IMI). The change reflected the fact that the edito- rial office was located at IMI and that the editors were formally employed at Stockholm University.

New techniques to process manuscripts were implemented by the publisher. In 2001 Tellus became available in electronic form, and a few years later all back volumes from 1949-2000 were also made available in electronic form. Electronic submissions of manuscripts to Tellus started in 2001.

When Bert Bolin retired in 1990 Hilding Sundqvist became Editor-in-Chief (1990-1999). After Sundqvist’s retirement Harald Lejenäs served as Editor-in-Chief 1999-2012. Today Peter Lundberg is serving as Editor-in-Chief for Tellus A and Henning Rodhe for Tellus B.

Traditionally scientific journals have been available as paper copies or in electronic form through subscriptions handled by a publisher. During the last years Open Access publication has become common. Many organizations like research councils require that scientists they support should publish their articles in Open Access journals in order to make the results available to the scientific community free of charge. IMI decided to adopt the new way of publication, and since January 2012 Tellus is an open access journal published by the Swedish publisher Co-Action. It means that separate issues no longer are published; accepted manuscripts appear on the publisher’s web site as soon as they have been accepted for publication. Today the topics covered by the two series are:

Tellus A: Dynamic meteorology; Data assimilation and predictability; Numerical weather prediction; Climate dynamics and climate modelling; Physical oceanography

Tellus B: Air chemistry; Aerosol science and cloud physics including related radiation transfer; Surface exchange processes; Long-range and global transport; and Biogeochemical cycles of carbon and other key elements.

BIENNIAL REPORT 2011 – 2012 9

THE INSTITUTE

THE DEPARTMENT OF METEOROLOGY AT STOCKHOLM UNIVERSITY The Department of Meteorology at Stockholm University (MISU) is the leading academic institution in meteorology in Sweden, conducting research into four main specialties: Dynamical Meteorology, Chemi- cal Meteorology, Atmospheric Physics and Physical Oceanography. MISU also has a rich educational program, consisting of a BSc-program in Meteorology, a MSc-program in Atmospheric science, Ocean- ography and Climate and a PhD-program in Atmospheric science and Oceanography.

Within Stockholm University, MISU is organizationally tied to the Physics and Mathematics Section of the Faculty of Science, while the International Meteorological Institute (IMI) is an integral part of the department, but with a separate economy as an independence institute within Stockholm University, with its own budget. MISU was established in 1947, when world-renowned meteorologist Carl-Gustaf Rossby came back to Sweden after a long and very successful career in the USA. He assumed the duties of the first Chair in Meteorology in Stockholm, created for him at Stockholm’s Högskola (later Stockholm Uni- versity). IMI was formed some time later, by a parliamentary decision in 1955. At Rossby’s untimely death in 1957, Bert Bolin took over the leadership of the department, a role that he maintained for almost three decades.

The small research group that Rossby created soon developed into a successful department with a vigorous international network. At the same time, the university structure has changed dramatically since Rossby’s days, especially since the promotion reform around the turn of the century. Instead of one or a few very influential professors, holding Chairs in their subjects and leading whole departments, there are now many professors, each with his or hers individual specialties and the department leadership is a role taken on by colleagues on the principle “primus inter pares”. Today, MISU is a mid-sized department at Stockholm University, with about 70 employed including more than ten permanent faculty, of which nine are professors, almost 30 graduate students, many junior scientists and a professional administration.

In 2006 the department also became a part of a virtual centre for climate research, in collaboration with three other departments at the university. This was made possible by a so-called “Linneus Grant”, for the Bolin Centre for Climate Research, named on honor of Bert Bolin. The centre promotes studies of climate, climate change and variability, as well as processes of importance for the climate, and in addition to researchers from MISU involves scientists at the departments of Physical Geography and Quartenary Geology (INK), Geological Sciences (IGV) and Applied Environmental Sciences (ITM). A Climate Re- search School is also attached to the centre. This centre cuts across several disciplines, temporal and spatial scales of climate research, and has transformed how this type of research is performed at Stockholm University. Since 2009 the centre is augmented by a strategic grant for climate modelling, and partly because of this MISU is now in a growing phase.

HEAD OF THE DEPARTMENT Ulla Hammarstrand, Lector Dynamic Meteorology. Until 31 July 2012

Michael Tjernström, Professor of Boundary-Layer Meteorology. From 1 August 2012

10 BIENNIAL REPORT 2011 – 2012

INTRODUCTION

BIENNIAL REPORT 2011 – 2012 11

INTRODUCTION

INTRODUCTION The main goal of IMI is to promote international scientific co-operation within meteorology. In accordance with this, scientists at the institute collaborate within many international research projects. Some of these are a part of the World Climate Research Programme (WCRP), the World Weather Research Pro- gramme (WWRP) or the International Geosphere-Biosphere Programme (IGBP). Funding for some of the projects has come from the European Union Framework Programme (e.g. EUCLIPSE), from the Euro- pean Space Agency (ESA), or from the Office of Naval Research.

EC-Earth is a European project to develop and use a new Earth System model. The EC-Earth project is conducted as a European consortium of scientists from about 20 universities, research institutes and Na- tional Weather Prediction centers. KNMI, the Netherlands, ECMWF and the Rossby Centre at SMHI are leading partners. Scientists at the institute within dynamic meteorology, physical oceanography and chemical meteorology are participating in the project. EC-Earth participates with simulations to the Cou- pled Model Intercomparison Project Phase 5 (CMIP5), and some of the runs for CMIP5 have been performed at MISU. The research results that originate from CMIP5 are evaluated in the Fifth Assessment Report (AR5), to be finalized at a meeting in Stockholm in September, 2013 .

Some Arctic projects also cut across the various sub-disciplines at the institute. The Arctic Summer Cloud-Ocean Study (ASCOS) involves partners from many countries and is lead from MISU. ASCOS aims at understanding the formation and lifetime of Arctic summer low clouds, and started with a research expedition on the Swedish ice-breaker Oden to the central Arctic Ocean during the summer 2008, as a part of the International Polar Year. Work on evaluation the observational data collected still continues. SWERUS-C5 is a joint Swedish-Russian-US research program to investigate the climate-cryosphere- carbon interactions in the East Siberian Arctic Ocean. At the end of 2011 preparations began for an Arctic expedition with Oden 2014. Scientists at the institute will participate both within dynamic meteorology and physical oceanography. Another international Arctic project with participation from the institute is the Polar Prediction Initiative launched by the World Weather Research Programme (WWRP). It is in the preparatory phase since 2012, and planning a Year of Polar Prediction during 2017-2018.

Several collaboration projects in dynamic meteorology concern model development. The GEWEX At- mospheric Boundary Layer Study (GABLS) aims at improving boundary-layer descriptions in general, and involves active collaboration with several research groups in Europe and USA. Moreover, there is long-standing collaboration with the Naval Research Laboratory on the COAMPS™ atmospheric model, and with the National Center for Atmospheric Research (NCAR), USA, on evaluating and developing the Community Earth System Model. This collaboration was also instrumental for the graduate course in climate modelling given by the Climate Research School during 2012, with international student participation.

MISU’s physical oceanographers are actively engaged in international collaboration in the Baltic Way programme, aimed at improving the physical and ecological state of this inland sea. All nations bordering the Baltic Sea are represented in the program by their marine agencies and oceanographically orientated university departments. The Esonet program represents a concerted European effort to establish permanent sea-bed observatories in the Atlantic proper as well as in marginal seas for long-term monitoring purposes.

Besides a strong participation in ASCOS the Chemical Meteorology group has continued its involvement in the international Atmospheric Brown Cloud (ABC) project with focus on measurements in The Mal- dives and in Nepal. The main MISU/IMI contribution to ABC is to seek a better understanding of the atmospheric life cycle of soot. The group is also actively involved in examining and developing model tools for understanding aerosol-cloud interaction on a global scale (in addition to collaboration within EC-Earth community, also with UiO/MetNo using the Oslo-CAM model), and on a regional scale over the Arctic (GRACE project), Amazon (AVIAC project) and Europe (MACCII project).

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INTRODUCTION

The Atmospheric Physics group is involved in a number of international satellite, rocket and ground- based projects as well as modelling studies concerning the middle atmosphere. Members of the group contribute to the mission preparation of the ESA Earth Explorer Atmospheric Dynamics Mission Aeolus, to provide global line-of-sight wind profiles using a Doppler-wind lidar. The launch is expected late 2013. The group has also been deeply involved in collaboration with several international partners concerning the Odin satellite mission; launched in 2001 Odin continues to provide a wealth of atmospheric data. Be- yond Odin, new middle atmosphere satellite collaborations concern ESA's plans for PREMIER, NASA's AIM satellite mission, the European ENVISAT community, and the ACE mission on the Canadian Sci- Sat.

The Atmospheric Physics group has also continued to collaborate in international rocket programs with instruments deployed in rocket launches led by several collaborators. The group also participated in two rocket projects within the extended ALOMAR Research Initiative (eARI), an opportunity funded by the European Commission, and now lead the preparations for the comprehensive international rocket project PHOCUS from Esrange, Sweden, in summer 2011.

Michael Tjernström is a member of the Science Advisory Committee of the ECMWF, vice Chair in the Atmospheric Working Group (AWG) of the International Arctic Science Committee (IASC) and member of the board for the Swedish Secretariat for Environmental Earth System Science (SSEESS). He has also been a member of the Science Steering Group of the International study of Arctic Change (ISAC). Caro- line Leck is a member of Surface Ocean Lower Atmosphere Study (SOLAS) implementation committee and is the Chair of the Swedish National Committee on Geophysics (IUGG and SCOR). Gunilla Svens- son is the co-chair of the GEWEX Atmospheric Boundary Layer (GABLS) and a member of the Science Steering Committee for the Global Atmospheric System Studies of which GABLS is a part. She is also a member of the Science Steering Group for the WWRP Polar Prediction Project. Heiner Körnich is a member of the Mission Advisory Group of the ESA Earth Explorer Atmospheric Dynamics Mission Aeo- lus and Annica Ekman is a member of the International Commission on Clouds and Precipitation (ICCP). Henning Rodhe has been the vice chair of the Atmospheric Brown Cloud (ABC) Science Team.

Besides the formalized collaborative projects mentioned above, scientists at the institute have also been involved in innumerable informal international projects, as can be seen from the publication list at the end of this report. IMI greatly facilitates such collaboration by its visitors program.

In the following section, a brief account is given of the activity at the four research groups at the institute, followed by two articles where Jost Heintzenberg and Raymond Pierrehumbert, who have been frequent IMI-guests for many years, give a personal account of what their visits have meant to them. Then there are four articles where some of the research conducted at the institute is described in depth on a popular level. Finally, the scientific articles published by scientists at the institute since 2009 are listed.

BIENNIAL REPORT 2011 – 2012 13

RESEARCH ACTIVITIES

14 BIENNIAL REPORT 2011 – 2012

RESEARCH ACTIVITIES

BIENNIAL REPORT 2011 – 2012 15

RESEARCH ACTIVITIES

RESEARCH ACTIVITIES This chapter contains the following subjects:

• RESEARCH GROUPS

• HOW IMI SHAPED MY SCIENTIFIC LIFE, BY JOST HEINTZENBERG

• FOND MEMORIES FROM STOCKHOLM, BY RAYMOND PIERREHUMBERT

• GLOBAL DYNAMICAL COUPLING IN THE MIDDLE ATMOSPHERE

• CLIMATE MODELING AS A SCIENTIFIC TOOL TO UNDERSTAND OUR CLIMATE AND CLIMATE CHANGE

• WHY DOES THE ATLANTIC OCEAN FORM THE NORTHERN HEMISPHERE DEEP WATER ?

• ARCTIC CLIMATE CHANGE

• LIST OF PUBLICATIONS

RESEARCH GROUPS

ATMOSPHERIC PHYSICS The Atmospheric Physics group (AP) at MISU/IMI tence. Central experimental activities are con- runs a research programme on the aeronomy of the nected to the Swedish Odin satellite as well as the middle atmosphere. Focussing on the altitude use of Esrange Space Centre in Northern Sweden range 10-100 km, the field of research of our At- by means of sounding rocket launches and lidar mospheric Physics group concerns in particular operations. Complementary model studies are es- radiative and chemical interactions of aerosols and sential to put our experimental results in a larger trace gases as well as dynamical and chemical perspective of understanding the middle atmos- coupling between different regions of the atmosphere. Ongoing model studies range from the mi- phere. In the middle atmosphere, aerosol particles crophysics of particle formation to global dynam- of interest include ice clouds, particles of meteoric ics. origin, and the background aerosol formed by conversion from various gases. The long-term goals for our atmospheric physics programme at IMI/MISU are: Our research programme in this field includes a • to establish the distribution and properties of wide range of experimental and theoretical tech- important trace gases, aerosols and clouds in the niques. The experimental component aims at the middle atmosphere, development, improvement and application of • to understand underlying transport processes and measuring techniques for in-situ and remote sens- the dynamical coupling between various parts of ing studies. Spectroscopic techniques and particle the atmosphere, microphysics are examples of particular compe-

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• to obtain a better understanding of the micro- . physical, radiative, and chemical interactions that determine the properties and variability of trace gases, aerosols, and clouds.

CHEMICAL METEOROLOGY The research in chemical meteorology (CM) in- The CM group at MISU/IMI is involved in the volves studies of the occurrence and transforma- ABC-project (www-abc-asia.ucsd.edu/) and the tion of chemical constituents in the atmosphere as ARDEX project, which both aim at a better under- dependent on homogenous and heteorogenous standing of the atmospheric life cycle of soot and chemical reactions and meteorological conditions: its climate effects over the Indian sub-continent winds, clouds, precipitation etc. Several of the and the surrounding oceans. ASCOS research projects are motivated by the concern (www.ascos.se) and GRACE about the effects of anthropogenic changes in the (http://www.itm.su.se/page.php?pid=680), are two chemical composition of the atmosphere: impact efforts that are focused on high-latitude atmos- on climate, ecosystems - including acidification – pheric sources of aerosol particles and their role in and human health. cloud formation and Arctic climate change. The project AVIAC (http://www.itm.su.se/page. Studies of the occurrence of aerosol particles and php?pid=658) attempts to study the interaction gaseous constituents of importance for cloud for- between aerosol particles and clouds over the mation, biogeochemical cycles and climate play a Amazon, and AFaCC (http://www.itm.su.se/page. central role in the research activities. The research php?pid=803) aimes at studying the interaction is carried out as part of comprehensive interna- between aerosol particles and convective clouds. tional field campaigns measuring both in-situ and by remote sensing. The field-work is comple- The CM group is also a partner in developing the mented by laboratory studies and theoretical mod- description of aerosol particles and their influence elling of different complexity to examine how on clouds and climate in different global climate different chemical constituents interact with at- models, including CAM-Oslo and EC-Earth mospheric mixing and transport. The models are (www.ecearth.knmi.nl). We also perform molecu- used to interpret both the in-situ and remote sens- lar dynamic simulations in collaboration with part- ing collected data and to study the impact of long- ners at the Swedish Royal Institute of Technology term past and future changes in atmospheric com- and host a newly developed large-eddy simulation position. model for detailed studies of aerosol-cloud interaction.

DYNAMIC METEOROLOGY Research in the area of dynamics covers processes model with all available observations assimilated. from the global scale down the turbulent scales. Examples of studies are analyses of the Hadley The large scales concern the general circulation of circulation, of the position and variability of the today, the past and the future. Many of the studies Atlantic jet stream, of the occurrence of coastal of present climate are based on so-called reanalysis low-level jets, and of the general characteristics of products, i.e. global gridded fields of all relevant the storm tracks, including the preferred dynamical meteorological variables with a typical time resolu- setting for extreme storms that take landfall in tion of hours, available from international weather Europe to develop. prediction centers. These fields are constructed using a Numerical Weather Prediction (NWP)

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Small-scale dynamic motions, smaller than the A common denominator for many of the studies in computational grid in a climate or NWP model, are dynamic meteorology is the use of numerical mod- boundary layer and mesoscale processes. The latter els. They are frequently used, mostly in combina- can be resolved in high-resolution models, but the tion with observational data, in many different boundary layer, which is dominated by small scale ways to study fundamental aspects of the dynamics turbulent motions, is not directly resolved for at- as well as the interaction between different scales. mospheric conditions. Research in this field is These models range from simplified models of the motivated by the effect those motions have on the atmosphere to global and regional NWP models, larger scale, and by the need to skillfully imple- Single Column Models (SCM), Large Eddy Simu- ment these effects in larger-scale numerical models lation (LES) and regional and global climate mod- for weather and climate. Regional studies include els (discussed in a separated chapter). Simplified monsoon circulation and coastal flows. Paleocli- models are used to investigate the impact of or- mate studies concern deep-time climate change as ganization on the large-scale circulation of convec- well as the more recent Holocene climate. Much of tive clouds that are of smaller size than the compu- the science is done in collaboration with national tational grid of a NWP model. and international collaborators.

PHYSICAL OCEANOGRAPHY A large part of the research in the physical ocean- models are the vertical and latitudinal transport of ography (OC) group at MISU/IMI uses numerical heat and freshwater. models, but observational work (primarily using satellite altimetry) and theoretical work is also We have earlier developed a practical way of com- done. Some of it is global, and some is regional puting the energy of the internal waves that are with an emphasis on the Baltic Sea and the Nordic excited by tidal currents over rough bottom topog- Seas. Our main tool for global modelling is the raphy. The deep overturning circulation is largely NEMO model, which is also the ocean component driven by the vertical mixing caused by breaking of EC-Earth, a joint European coupled climate internal waves. This method has now been used for model. We have also participated in the develop- various applications, such as the parameterization ment and the evaluation of NEMO. of the bottom drag in tidal models and the interpre- tation of sediment transport data. The OC group has been very active in developing new diagnostic tools for analysing the global over- Some of our regional modelling work concerns the turning circulation. The traditional way to do this Arctic Ocean; both its modern circulation (in col- is to compute the overturning stream function in laboration with SMHI) and its paleo-circulation (in depth-latitude coordinates; density-latitude coordi- collaboration with the Department of Geological nates are also often used. New methods recently Sciences). The Baltic Sea is studied in collabora- developed at MISU/IMI include using depth- tion with SMHI, using general circulation models. density coordinates, which provides a transparent These are used both for physical oceanographic picture of the energetics of the overturning, and applications and for biogeochemical studies, for temperature-salinity coordinates, which displays example studies of the transport of larvae. The the water-mass transformation and provides a link transport predictions of the models have also been with the traditional observational oceanography. validated by experimental studies with surface Related subjects that have been studied with global drifters.

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HOW IMI SHAPED MY SCIENTIFIC LIFE Jost Heintzenberg

In fall 1975 the American colleague Bob Charlson, When I first visited IMI I was rather unsure if it whom I worked with at the time as a visiting scho- was a good place for fruitful long term scientific lar, and who had been at IMI may times recom- work or if it was sort of a dead end in a small mended this institution to me and also recom- scientific community having little contact with mended yours truly to his Swedish friend Georg frontline research elsewhere. Soon I became con- Witt at Stockholm. Georg then kindly invited me vinced that it wasn’t a dead end at all when I my- as an IMI guest researcher when I was back in self got the chance to invite colleagues from all Germany, and already in early summer of 1976 I over the world for fruitful shorter and longer visits, got a chance to participate with my instruments in learning from their courses and from their theoreti- an aerosol field campaign organized jointly by the cal and experimental expertise, and doing laborato- Atmospheric Chemistry and Physics groups of ry and field experiments that were greatly en- MISU in the deep forest between Lake Mälaren hanced by the IMI guests. There was one more and Lake Vättern. Living with the Stockholm important factor that made the department attrac- students and technicians in a closed nearby youth tive to an aspiring young scientist: A very well hostel, fighting the logistic challenges of a field stocked library with the service of a highly compe- campaign in Swedish back country and even hav- tent and dedicated librarian, both supported by IMI ing to fight an enormous wood grouse, who did not funds. like us invading his territory, gave me many insights into Swedish nature and culture. Many deep personal friendships were established with IMI guests, some of which resulted in highly I enjoyed myself, and my Swedish colleagues were successful semi-permanent collaborations that happy enough with me to invite me for a one-year lasted long after I left MISU in 1993. To me the stay at IMI in 1977. I gladly accepted because it three most important guests were John Ogren, finally gave me chance to leave the university for Dave Covert, and Keith Bigg. With John and Bob good, at which I had spent all student and some Charlson I developed a new type of cloud sampler post-doc years. This time I was to work more with that opened up a whole new way of monitoring Georg Witt, who introduced me to his rocket stu- cloud composition. With Dave I conducted many dies of the mesosphere and made me derive size valuable (and fun) aerosol experiments in Ham- distributions of mesospheric noctilucent cloud burg, on Spitsbergen, on the Swedish icebreaker particles from multispectral optical data – some- Oden , and in the laboratory. The third, and maybe thing that I would never have ventured into delibe- for IMI most important one of the three guests, rately. However, through this work I learnt a lot Keith Bigg, participated as IMI guest in three Oden about particle optics, Mie theory, and its exten- expeditions to the North Pole and has been a conti- sions to non-homogeneous particles. nuous source of inspiration to me and others in Stockholm. It did not seem easy to lure Keith from Georg encouraged me to extend my visit and apply the warm Australia to boreal Scandinavia, and to the Swedish Natural Research Council (NRC) potentially even more difficult to convince him to for a research grant that would fund my own salary join an icebreaker expedition to the North Pole, but plus some experimental resources. Being appar- he had been by ship to Antarctica through much ently the first who proposed to study soot in the rougher southern seas and, maybe more important- atmospheric aerosol lead to several years of NRC- ly, I could promise a whole new world of Arctic funding, during which I could establish my self at birds to this dedicated bird watcher. So he came, MISU. One of the main reasons for my wanting to stayed, made friends, came back many times and stay at MISU/IMI was the continuous stream of stimulated a long row of prominent joint publica- prominent atmospheric scientist, who came to tions. Taken all together I am grateful for about Stockholm as IMI guests and whom I was exposed thirty of my peer-reviewed papers that came about to and could learn from in the many fields of re- because of IMI-funding, either with guests whom I search that were pursued at the department. had invited to IMI during my stay there or through my own visits as IMI guest.

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After my return to Germany in 1993 about 15 years at MISU/IMI. It feels good to be able to years ensued, in which building up the newly revive soot instruments that I had built some 25 founded Institute for Tropospheric Research (IfT) years ago because the research on soot in the at- at Leipzig kept me from frequent IMI visits. In- mosphere has by no means been exhausted in the stead, I encouraged students and researchers based meantime, and I enjoy applying data analyzing at IfT to go to IMI for doctoral or post-doc studies tools that I developed in the meantime to new re- and for their participating with IfT-instrumentation sults that have been derived at IMI. During these in the Oden expeditions. Since my retirement in visits I happily sense that the IMI spirit of stimulat- 2010, however, I happily return myself several ing international contacts and collaboration is be- times per year as IMI guest to teach in various ing cultivated with as much dedication as ever courses, and continue research in Chemical Mete- before. orology that I had helped to establish during my

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FOND MEMORIES FROM STOCKHOLM

Raymond Pierrehumbert

I have had the pleasure of a very long and produc- who was at MISU for many years. I taught a tive association with IMI, and have fond memories course in mountain meteorology, and had the plea- of the warm welcome my family and I have always sure of becoming acquainted with another of my received from Sweden, and of course the rich and favorite places in Sweden, the Abisko Research stimulating intellectual environment provided by Station, where I taught a mountain meteorology IMI/MISU. short course for the Swedish Air force. At the time there were many Air Force officers doing degrees Though I had interacted with various MISU facul- at MISU. ty, notably Bert Bolin and Erland Källen, at professional meetings earlier, my familiarity with MISU I have since returned to Abisko many times, in- dates mainly to a sabbatical I spent there in the cluding the dynamical systems meeting organized academic year of 1987. I was in transition at the there by Anders Karlqvist and John Casti, and time between the NOAA Geophysical Fluid Dy- most recently two Bolin Center Arctic Climate namics Laboratory and Princeton University Summer Schools. Many summers, my family has (which turned out to be a rather brief stop before enjoyed long hiking trips in the area around Ab- moving on to the University of Chicago), and this isko, and in both Padjelanta and Sarek. Both my was my first sabbatical. My wife, Janet, was also children have fallen in love with the North, and on sabbatical, from what was then Bell Labs, and now that they are grown have continued with trips spent the year at the famous Talöverföring och of their own. Last summer, my younger daughter Musikakustik lab of the KTH. We had just the one Nadia wound down before starting graduate daughter at the time, Anna, who was warmly wel- school, by doing a solo hike from Abisko to Sulit- comed into dagis after making it through the rather jelma, via Kebekaise. long dagis queue common at the time. The able IMI secretariat found us a lovely apartment on That sabbatical year provided time to get involved Upplandsgatan, and for many years Vasastan was in many new areas of research. It was the year I our favorite kvarter in Stockholm, though in recent began my work on Hamiltonian chaos, chaotic years my heart has been more captured by Söder. advection and large scale mixing, which has been a Courtesy of the generosity of government-provided major theme of my work ever since. I did my first lessons, I set about learning Swedish, and ever calculations of the sort, which had relevance to since Stockholm has felt like home to me and my atmospheric water vapor and stratospheric chemi- family every time we return. stry, and wrote my first papers on the subject, during that sabbatical year. In addition, my sabbatical At the time, MISU was still using Apple II com- at IMI provided my first real exposure to the excit- puters, ethernet wasn't yet common, and the inter- ing developments in aerosols, and in cloud micro- net was a gleam in the eye of a few ARPA-funded physics being pioneered in MISU at the time. I'm geeks back in the US. All of us at MISU had to get gratified to see how many of the young researchers our output back from the ECMWF Cray in the working at MISU at that time have gone on to be- form of text emails, and there was a lot of creativi- come major figures in the subject, many of them, ty in homebrew ways of encoding binary data and happily, still working at MISU or elsewhere in graphics as text. I believe I brought the first 512K Stockholm. My only regret from those years was beige toaster Macintosh to appear at MISU along that I was not yet sufficiently aware of the deep with me. In those days I was still primarily a geo- scientific questions being asked about the carbon physical fluid dynamicist, and had no real cogniz- cycle to allow me to take advantage of Bert Bolin's ance of the interesting things going on with radia- insights. I did not get involved in carbon cycle tive transfer or the hydrological cycle. My primary work until I was working with David Archer on interests were baroclinic instability, large scale putting together the University of Chicago Global planetary waves, multiple equilibria and stratified Warming course (which now has the highest flow over mountains. In these areas I found plenty enrollment of any class at the University). It was to talk about with Erland Källen, Åke Johansson nevertheless a privilege to have had the opportuni- and my first MIT PhD student Brian Reinhold, ty to know Bert, even a little bit.

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While I have not since been back for a full sabbati- deal from what I have learned from Michael cal year, I have happily had many other opportuni- Tjernström, Gunilla Svensson and Caroline Leck. ties to return to IMI/MISU for collaborations with And as I've gotten more deeply into the many is- colleagues there. I've taught in an EU climate sues of how both absorbing and reflecting aerosols school at MISU, and my lectures there formed affect climate, I've been able to interact more and much of the basis of the paleoclimate parts of more with the many MISU researchers in this area Chapter I of my textbook, Principles of Planetary who in turn draw their inspiration from Henning Climate. More recently, I taught part the Rodhe. On a wide-ranging set of issues dynamical MISU/IMI graduate course in climate modeling, and otherwise, I have enjoyed my discussions with and courtesy of the generosity of MISU and IMI I Johan Nilsson, Jonas Nycander (whose PhD de- have been able to spend three Septembers at fense at Uppsala I attended during my sabbatical), MISU, establishing new research collaborations Kristofer Döös and MISU friends new and old far with MISU colleagues. I'm especially excited by too numerous to name. While I may or may not the current project I have going on sea ice seasonal ever become as much of a fixture around cycles with Rodrigo Caballero (who, I'm proud to IMI/MISU as "resident American" Bob Charlson, I say, was one of my postdocs at the University of very much value the time I am able to spend at Chicago). Since clouds and the boundary layer are MISU and look forward to a lot more of it in the a key part of the behavior, I have profited a great future.

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GLOBAL DYNAMICAL COUPLING IN THE MIDDLE ATMOSPHERE Bodil Karlsson, Jörg Gumbel

The state of the mesosphere is connected to the phere, such as weather systems, jet streams or oro- lower atmosphere through various dynamical graphy. While propagating to mesosphere, gravity coupling processes. The study of these coupling waves are filtered by the wind patterns at lower processes by means of global satellite observations altitudes. Any changes in the lower atmospheric and numerical modelling has been a major focus of wind pattern therefore lead to modifications of the atmospheric physics research at MISU/IMI during gravity wave spectrum and, thus, modify the driv- recent years. Figure 1 shows the general vertical ing of the mesospheric circulation. This is the basis structure of the atmosphere in terms of typical for the global coupling processes (or "teleconnec- temperature profiles. Figure 2 is a schematic repre- tions") between the lower atmosphere and the me- sentation of major dynamics patterns in the middle sosphere described below. atmosphere. The general circulation in the mesosphere is characterised by a global-scale meridional Noctilucent clouds (NLC, see Figure 3) are the summer-to-winter flow. This flow is driven by the highest clouds in our atmosphere and occur in the breaking of gravity waves and the resulting mo- summertime upper mesosphere at altitudes be- mentum transfer. The sources of these gravity tween 80 and 90 km. waves are various disturbances in the lower atmos-

Figure 1: Typical temperature profiles through the middle atmosphere for "usual" conditions (blue) and for polar summer conditions (red). Note the shift towards a very cold and low mesopause during polar summer. The profiles shown here are taken from the climatological model atmosphere MSIS.

Figure 2 : Schematic of the dynamical processes involved in global coupling processes in the middle atmosphere. Blue lines represent meridional mean circulation patterns in the stratosphere and mesosphere. Red lines represent upward propagating gravity waves whose breaking drives the global-scale circulation in the mesosphere. Noctilu- cent clouds (NLC) occur in the high-latitude summer mesosphere where large-scale updraft leads to extreme adiabatic cooling and temperatures down to 100 K.

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Figure 3: Noctilucent clouds (NLC) as observed from Stockholm. In summertime twilight conditions, the lower atmosphere is in darkness while these clouds at 80-90 km altitude are still reached by the Sun. As a result, they appear as "night-shining" clouds in the summer sky.

Their occurrence is directly related to the mesos- Canada, Finland and France, and since 2007 oper- pheric circulation pattern. The meridional summer- ated as an ESA Third Party Mission. The Optical to-winter flow drives high-latitude temperatures far Spectrograph and InfraRed Imager System from radiative equilibrium and results in an ex- (OSIRIS) onboard Odin provides comprehensive tremely cold summer mesopause with temperatures data on the occurrence and properties of NLC. as low as 100 K. Under these conditions, clouds Using these NLC observations as a tracer for me- can form despite the very lower water concentra- sospheric variability, major achievements of the tions at these altitudes. Odin mission have concerned our understanding of the global dynamics of the middle atmosphere. Studies of the mesosphere and NLC have a long tradition at MISU/IMI and reach back more than 50 years. For most of this time, NLC studies have focused on the understanding of the clouds them- selves. This research has involved ground-based observations, sounding rocket experiments and microphysical studies. In this way, atmospheric physics research at MISU/IMI has contributed substantially to the comprehensive knowledge that we have about these clouds today. As a result of this improved understanding, we have been able to shift our focus from NLC as an object of our research to NLC as a tool for our research. As these clouds are extremely sensitive to thermal conditions and the underlying atmospheric circulation, we can use them as excellent tracers for processes in this part of the atmosphere.

An important basis for these studies has been the Figure 4: The Swedish-led Odin satellite has been in orbit since 2001, providing us with comprehensive data on the Odin satellite mission (see Figure 4). Odin is a Earth's middle atmosphere. Swedish-led project funded jointly by Sweden,

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Figure 5. Odin satellite observations of NLC occurrence frequency in the latitude band 60 °-80 ° during 20 summer seasons. The top panel shows data from the northern hemisphere summer, the bottom panel shows data from the southern hemisphere summer. Time on the x-axis is given as days relative to summer solstice. Dashed lines indicate data gaps during periods when Odin did not perform mesospheric observations.

Figure 5 shows mean NLC occurrence frequencies season starts very consistently 20-25 days be- in the latitude band 60°-80° obtained from the fore summer solstice (i.e., at the end of May). northern summer 2002 until the southern summer In the southern hemisphere, there is large year- 2011/2012. Occurrence frequency is defined as the to-year variability in the onset of the season. number of observations with identified NLCs divided by the total number of observations. Both of these features are manifestations of the large-scale circulation patterns in the middle at- Figure 5 reveals two striking features that are mosphere and the underlying global coupling me- closely related to the global coupling processes chanisms. Below, we discuss the first feature in described above: terms of "inter-hemispheric coupling" and the • There are distinct differences in NLC occur- second feature in terms of "intra-hemispheric rence between the northern and southern he- coupling". misphere: NLC in the northern hemisphere are more frequent and show significantly less year- Inter-hemispheric coupling denotes the dynamical to-year variability than in the southern hemis- control of the summer mesosphere by the lower phere. (An exception is the northern hemisphere parts of the winter hemisphere. The existence of summer 2002 that featured unusually few this surprising teleconnection was first suggested NLC.) by model studies, supported by local observations of mesospheric conditions. Subsequently, global • There are distinct differences in the onset of the observations of NLC by Odin have confirmed this NLC season between the northern and southern remarkable connection between the two hemis- hemisphere: In the northern hemisphere, the

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pheres, both on a year-to-year basis and on an intra-seasonal basis. A basic result is that the larger dynamical variability of the northern hemispheric winter stratosphere causes a more variable and weaker NLC season in the southern hemisphere summer mesosphere. In the winter stratosphere, a very stable flow pattern can develop known as the polar vortex. During stable polar vortex conditions it is easy for gravity waves to propagate through the stratosphere and to drive the circulation of the mesosphere. However, when disturbances occur in the stratospheric circulation, more and more wind patterns emerge that can absorb part of the gravity wave spectrum. In general, due to the more uneven land-sea distribution in the northern hemisphere, the northern winter stratosphere features more disturbances in terms of planetary waves than the southern winter stratosphere. This results in less gravity waves reaching the mesosphere and, thus, a Figure 6: The relationship between summer mesosphere NLC weaker mesospheric circulation, less adiabatic occurrence and winter stratosphere conditions. Plotted along cooling of the southern summer mesophere and the x-axis is the anomaly in the NLC occurrence in July/January less southern NLC. Also the unusually low NLC for northern hemisphere (NH) summers and southern hemisphere (SH) summers, respectively. Plotted along the y-axis is occurrence in the northern summer 2002 (figure 5) the anomaly of the mid-stratosphere winter temperature field as fits well into this description as it coincided with a measure of planetary wave activity. The strong correlation large disturbances in the southern stratosphere that between both parameters is explained by inter-hemispheric coupling . led to a very unusual breakup of the Antarctic winter polar vortex during that year. As a matter of fact, the Antarctic winter stratosphere can occasionally be so stable that the polar Figure 6 shows an inter-hemispheric coupling vortex persists undisturbed well into the summer. analysis based on the Odin satellite dataset. There Again, this modifies the filtering of vertically is a clear correlation between stratospheric winter propagating gravity waves in the way that more conditions and mesospheric summer conditions. gravity waves reach directly into the summer me- Summer mesosphere conditions (along the y-axis) sosphere. As a consequence of the momentum are represented by the anomaly of NLC occurrence carried by these waves, this enhanced propagation frequency. Winter stratosphere conditions (along in the summer hemsiphere leads to a weakening of the x-axis) are represented by a stratospheric tem- the mesospheric circulation and, thus, a reduction perature anomaly as taken from ECMWF re- of NLC. Most prominently, the southern NLC analysis data. This temperature anomaly is a meas- season 2010-2011 started with a delay of more ure for stratospheric disturbances in terms of pla- than 20 days as compared to other years (figure 5), netary wave activity. Note that the southern hemis- which coincided with an exceptionally persistent phere NLC seasons SH04/05 and SH10/11 are polar vortex in the Antarctic stratosphere. apparent outliers from the anticorrelation in figure 6. As it turns out, these particular seasons can be Figure 7 plots our analysis of the relationship be- explained by competing dynamical effects related tween the persistency of the Antarctic stratospheric to a solar proton event and to a very persistent polar vortex and the onset of the NLC season in the Antarctic polar vortex, respectively. southern mesosphere. Based on ECMWF reanalysis data, the persistency is defined by the final Intra-hemispheric coupling, on the other hand, day when the zonal mean westerlies in the stratos- denotes the dynamical control of the summer me- phere decrease below a velocity threshold of 30 sosphere from lower altitudes in the same hemis- m/s. The NLC onset is taken from the Odin data in phere. As described above, the Antarctic winter figure 5. In accordance with the idea of an intra- stratosphere is less variable than the Arctic winter hemispheric coupling, a strong dependence of the stratosphere due to little planetary wave activity. NLC onset on the timing of the stratospheric wind

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transition is indeed observed. While there is no In conclusion, the state and variability of the me- obvious effect on the NLC onset for early stratos- sosphere are closely connected to the lower atmospheric vortex break-ups, late vortex break-ups phere through intra-hemispheric and inter- delay the NLC onset significantly. hemispheric coupling. These global-scale telecon- nections are prominent examples of the need to 0 treat the atmospheric system as a whole. NLC are

SH10/11 valuable tracers for such dynamical processes in −5 the middle atmosphere, and ten years of NLC data from the Odin satellite have been an excellent basis −10 for surprising discoveries. The observational data set has been complemented by comprehensive −15 model simulations that allow deeper studies of the SH06/07 mechanisms behind these processes. The −20 SH07/08 SH08/09 MISU/IMI atmospheric physics group has been strongly involved in such studies with the −25 SH04/05 Kühlungsborn Mechanistic general circulation SH03/04 model (KMCM) and the Canadian Middle Atmos- −30 SH02/03 SH09/10 phere Model (CMAM). We know today that both Start of NLC Season (DFS) intra- and inter-hemispheric coupling processes are −35 SH05/06 needed for an understanding of the behavior of the −40 Earth's mesosphere. −60 −50 −40 −30 −20 −10 Stratospheric Wind Transition (DFS) Details about this study and the mechanisms behind the dynamical coupling the middle atmos- Figure 7: Relationship between the start of the southern NLC phere can be found in a recent paper by J. Gumbel season and the end of the southern hemisphere winter polar and B. Karlsson (2011) and the references therein. vortex. The date of the stratospheric wind transition (x-axis) defines the end of the winter polar vortex based the stratospheric zonal wind speed. Dates are plotted as days from solstice (DFS). The vertical extent of some data points represents uncertainties. The observed correlation between NLC season and stratospheric polar vortex is explained by intra-hemispheric coupling.

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CLIMATE MODELING AS A SCIENTIFIC TOOL TO UNDERSTAND OUR CLIMATE AND CLIMATE CHANGE Gunilla Svensson

What is a climate model? tion with radiation. The effect of those motions and processes must be allowed to affect the motions on The climate of the earth is determined by the bal- the larger scales, and this is done by parameteriza- ance between the incoming short-wave radiation tions. These are built on advanced knowledge of from the sun and the thermal long-wave radiation the behavior of the small-scale processes gained back to space. A climate model is a representation from theory or fine-scale models but are also heav- of these energy fluxes and describes how the con- ily dependent on observational data. Such parame- ditions change if the system is perturbed by e.g. terizations introduce uncertainty in the GCM-based changes in greenhouse gas concentrations. Global simulations of future climate. climate models are the only scientific credible tool available to meet the societal need of prediction of The atmosphere interacts with the land surface and future climate change. This is because the climate with the oceans, and the ocean circulation as well system response to a perturbation involves com- as the sea-ice is therefore important for the climate. plex interactions and feedback mechanisms acting A coupled climate model includes a consistent on varous time scales between the atmosphere, the description of both the atmosphere and the ocean. oceans, the cryosphere, the biosphere, and the land Many of the current generation of global climate surface. A General Circulation Model (GCM) of models are under further expansion to become the atmosphere is the basis of all global climate Earth System Models (ESMs), which have both models. The numerical model is built on the physi- these physical components and an interactive car- cal laws for the atmospheric flow solved on a three bon cycle. The atmospheric component of the dimensional grid over the globe (Figure 1), with ESMs also includes aerosols, which are suspended typical horizontal resolution of about 100 km and particles in the atmosphere of both of natural and some 50 levels in the vertical. anthropogenic origin. Aerosols interact directly with radiation by absorption and scattering, and also act as condensation nuclei for cloud formation. The land component calculates the surface fluxes of energy and momentum, and may also include a terrestrial ecology component to simulate vegetation and soil carbon and other trace gases. The ocean component of an ESM may also include marine biogeochemistry and ecology. Both natural and anthropogenic influences on the climate system are thus captured by numerous types of emissions, variations of land surface albedo due to changes in vegetation and land use, and aerosol chemistry. Adding these different components to an ESM represents a major step forward in simulating the Earth's ecological systems in a comprehensive and internally consistent way.

Climate modeling at MISU Figure 1 . Schematic picture of the numerical grid for a global climate model and the physical processes that has to be para- MISU scientists take a very active part in the Bolin meterized, see text for more information. Courtesy of NOAA. Centre for Climate Research as one of its four cor- nerstone departments, especially in climate model- This resolution is coarse relative to the scale of ing. The Bolin Centre was established in 2006 as many motions in the atmosphere, for example syn- the result of a Linnaeus grant from the Swedish optic scale frontal systems and other important Research Councils VR and FORMAS. A govern- physical processes such as clouds and their interac- mental strategic grant for climate modeling was

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added in 2010 and research questions that can be and for the future represented by three different studied by using global and regional climate mod- scenarios. In the most extreme scenario (RCP8.5) els are increasingly addressed within the Bolin the Arctic is projected to have no summer ice by Centre and at MISU. the middle of this century. The paper (Koenigk et al., 2013), co-authored by MISU and Rossby Cen- Several models for regional and global climate tre scientist, discusses all aspects important for the studies are applied and used for different studies. Arctic climate and the sea ice in EC-Earth. MISU The last few years a considerable effort has been has also participated in the development and the put into the EC-Earth project by scientists at MISU evaluation of the ocean component of EC-Earth and the Rossby Centre, SMHI, that also participate (Sterl et al., 2012). in the Bolin Centre climate modeling effort. The EC-Earth consortium has partners from many An important part of climate model development is countries in Europe and is led from KNMI, the to evaluate the performance of the models with the Netherlands. In this project, we have contributed focus on special processes. Of special interest to with simulations to the Coupled Model Intercom- MISU scientists are small-scale processes, such as parison project Phase 5 (CMIP5) database. This aerosols, clouds and turbulence, which are not database forms the foundation for the research resolved by the model grid but still important for evaluated in the upcoming IPCC (Intergovernmen- climate. Clouds in the Arctic and the subtropical tal Panel on Climate Change) fifth assessment Pacific in the CMIP3 (predecessor to CMIP5) report (AR5) planned to be published in September model ensemble have been evaluated and com- 2013. This is the first time Sweden contributes to pared with mainly satellite data. From our studies, this internationally coordinated project with global it is clear that the models have problems with rep- climate model simulations. This achievement was resenting the clouds and their radiative properties made possible by the involvement in the EC-Earth in both locations (Karlsson et al., 2010, Karlsson project in combination with the computer system and Svensson, 2011; Svensson and Karlsson, Ekman/Vagn, dedicated for climate and turbulence 2011). In the Arctic the models underestimate the simulations and funded by the Knut and Alice atmospheric long-wave radiation to the surface in Wallenberg Foundation. Figure 2 shows results the winter. These problems are related to the ex- from of a number of EC-Earth simulations per- tremely cold environment and possibly the lack of formed for the CMIP5 project. The figure shows liquid clouds. the Arctic sea-ice extent for present day conditions

Figure 2 . March (dashed) and September (solid) sea ice extent in m2 in the northern hemisphere in the twentieth century simulations (black), RCP4.5 (blue), RCP8.5 (red), RCP2.6 (green) with EC-Earth and in satellite observations (stars). Reproduced from Königk et al., (2012).

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Figure 3. The simulated 10-m wind speed in a) CAM4, b) CAM5, c) ERA-Interim and the difference between d) CAM4 and ERA- Interim, e) CAM5 and ERA-Interim and f) CAM5 and CAM4. Reproduced from Lindvall et al., (2013).

The diurnal cycle in near-surface parameters such el (CCSM) and Community Earth System Model as temperature, wind and turbulent fluxes have (CESM). In the effort of expanding CCSM to be- been in focus in a collaborative project with the come a ESM, we have been involved in the im- National Centre for Atmospheric Research plementation of a new representation of naturally (NCAR), USA. A large network of flux station da- generated sea-salt aerosol particles over oceans ta has been gathered and used in the evaluation of (Liu et al., 2012). In yet another project, the cli- two recently developed versions of the atmospheric mate during the early Eocene (56 to 34 million part of the NCAR Community model (CAM4 and years ago) has been modeled with CCSM. Previous CAM5), which are both used in CMIP5 simula- efforts to simulate this very warm period in the tions. The description of the turbulent layer and the Earth's history were not successful in terms of diurnal cycle matters for example for the near sur- comparison with the available proxy data records. face wind climate, which is very different in the The proxy records showed a smaller temperature two versions, see Figure 3. CAM5 applies an extra difference between the equator and poles than the parameterisation of drag due to subgrid-scale oro- model simulations. No reasonable alteration in the graphy. This gives differences between CAM4 and models could reproduce it. In the end, after revisit- CAM5 (Figure 3.f) of between 4 and 6 ms-1 over ing the method for interpreting the temperature large continental areas. This is the first time obser- proxy data at low latitudes, it was possible to get a vational flux-data has been used in evaluation of general agreement between model and data (Huber the diurnal cycle. This is discussed further by and Caballero, 2011). However, very high concen- Lindvall et al. (2013). The method is presently trations of greenhouse gases were needed, almost used on results from other CMIP5 models. twelve times today's concentration of carbon diox- ide, and the general atmospheric circulation is very Several other studies involve the NCAR commu- different and is currently under further investiga- nity models, the Community Climate System Mod- tion.

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WHY DOES THE ATLANTIC OCEAN FORM THE NORTHERN HEMISPHERE DEEP WATER? Johan Nilsson

Background. Let us consider the basic processes controlling the decrease in salinity between the subtropical ocean The Atlantic Ocean stands out as the most saline of (~15–45 deg. latitude), where there is net evapora- the major ocean basins, as seen in Figure 1. The tion, and subpolar ocean (poleward of ~45 deg. difference in surface salinity between the North latitude), where there is net precipitation. The dif- Atlantic and the North Pacific is particularly strik- ference in evaporation minus precipitation (E-P) ing, and the Pacific surface salinity is significantly leads to a salinity contrast between the two re- lower than the salinity of the deeper layers, which gions, a contrast that is counteracted by north- stabilizes the water column and prevents deep wa- south salt exchange due to the ocean circulation. ter formation there. As a consequence, the Atlantic Thus, a large E-P difference or a weak circulation Ocean forms all deep water in the northern hemis- yields a large salinity contrast, and hence to low phere and therefore carries an anomalously large subpolar salinities. northward heat flux. A possible shut-down of the Atlantic deep water formation has played a leading One explanation for the low salinities in the North role in many hypotheses of past and future abrupt Pacific is simply that the net precipitation per unit climate reorganizations. area is greater there than in the North Atlantic. The basin difference in the hydrological cycle is largely The physical reasons for the asymmetry between controlled by the distribution of mountains that the Atlantic and Pacific oceans have been studied selectively block the zonal flow of moisture. In and debated by oceanographers and meteorologists particular, the low-leveled Central America in the for over a century, but the question is still not fully trade wind belt promotes an export of freshwater resolved. Numerous hypotheses have been pro- from the Atlantic, which was emphasized some 50 posed to explain the asymmetry in circulation and years ago by Dietrich and Weyl. In this view, the hydrography between the basins.

Figure 1: Surface salinity in the World Ocean. At the southern tip of Africa there is a transport of relatively saline upper ocean water from the Indo–Pacific to the Atlantic. This salt transport, known as the Agulhas leakage, contributes to making the Atlantic more saline than the Pacific.

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basin asymmetry in flow and salinity is thus exter- two narrow land barriers extending southward nally controlled by geographical asymmetries. A from the North Pole; southward of their termina- hypothesis in same spirit invokes the more north- tion point, there is a circumpolar southern ocean. eastward orientation of the North Atlantic storm Note that the land barriers are flat and hence have track, which enhances the wind-driven oceanic salt no topographical influence on the atmospheric exchange between the subtropical and subpolar circulation. regions. The starting point of the investigation is a configu- The oceanic salt-advection feedback hypothesis ration where both basins are 180 degrees wide and provides a radically different explanation, and both land barriers end at 50 degrees south as allows the ocean circulation to have multiple equi- shown in Figure 2. In this setting, our coupled librium states. This notion builds on a theoretical atmosphere–ocean–sea-ice model has been able to idea conceived by Stommel in 1961 that was in- attain a symmetric climate state, with deep sinking voked as an explanation for Atlantic–Pacific in both basins, as well as asymmetric Atlantic– asymmetry by Walin and Broecker some 20 years Pacific like states, with the sinking confined to one later. Central to this idea is the fact that the merid- of the basins. In the symmetric state, the time- ional gradients due to temperature and salinity mean climate conditions are essentially invariant have the opposite effect on the density gradient: under a translation by 180 degrees in the zonal the temperature gradient acts to drive the surface direction. This is noteworthy as there is significant water polewards, whereas the salinity gradient acts internal variability of the atmosphere–ocean circu- to drive the surface water equatorwards. Thus, if lation over a broad range of time scales. In the the subpolar salinity would increase, the poleward asymmetric states, the basing forming the deep flow would also increase. This would bring more water is systematically warmer and more saline saline subtropical water into the high latitudes, than the other basin, leading to larger zonal climate thereby increasing the salinity further. This salt variations. In these states, the salt-advection feed- advection feedback has the potential to tip the back spontaneously breaks the symmetry inherent ocean circulation into an Atlantic-Pacific like con- in the identical basin geometry. Thus, the salt ad- figuration with the deep water formation confined vection feedback is vigorous enough to create mul- to one of the basins. However, the feedback could tiple climate states in this fully coupled model, in principle locate the deep water formation to which has mid-latitude weather systems and a sea- either of the basins. Thus, in the strong version of sonal cycle. the salt advection feedback hypothesis, the reason for the high Atlantic salinity is found in the past Next we examined how a difference in the south- evolution of the climate system. ward extent of the two land barriers affects the ocean circulation and climate. Initially, we focused The role of basin geometry for the salinification on the case with two equally wide basins. Thus, the of the Atlantic. key geometrical asymmetry is that one of the basins is “Atlantic” in the sense that its western land The salt-advection feedback hypothesis raises two boundary is longer than the eastern boundary. A fundamental questions. First, is it powerful fundamental question is whether the “Atlantic” enough, given the presence of additional strong basin always is the preferred site of deep water atmosphere-ocean feedbacks? Second, can asym- formation. Our experiments show that depending metries in ocean basin geometry override the salt on the termination latitudes of the two land barriers advection feedback and remove the equilibrium either the “Atlantic” or the “Pacific” basin can be with North Pacific sinking? To examine these the preferred site of the deep sinking. Here, the questions, I have together with scientists from MIT wind distribution plays a critical role: if the short and Copenhagen University designed a suite of continent ends in the latitude band of southern coupled climate model experiments in which hemisphere easterly surface winds, then Atlantic asymmetries in the basin geometry are gradually sinking is favored; whereas if the short continent introduced (Nilsson et al., 2013). The geometrical extends into the band of westerly surface winds, layout is a planet mostly covered by ocean, with then Pacific sinking is favored.

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Figure 2 : Surface salinity in an identical two-basin geometry, where both continents ends at 50 S, which has multiple equilibrium climate states: A symmetric state with deep water formation in both basins (upper panel) and two asymmetric Atlantic–Pacific like states with deep water formation in olny one of the two basins (lower panel). Note that the second land barrier is hardly visible but located near 180 degrees E/W .

A part of the explanation is that the zero wind line turning in the Atlantic. Thus, via the Agulhas leak- (located near 30 deg. south) is encountered near age the Atlantic overturning circulation can pro- the maximum curl of the surface wind stress. In a vide a basin-scale salt-advection feedback. seminal paper, published in 1947, H. U. Sverdrup demonstrated that the zonal flow of upper-ocean However, our numerical experiments demonstrate thermocline water should be westward equator- that when “Africa” extends into the band of westward of this latitude and eastward on the poleward erly surface winds, the direction of the “Agulhas” side. This wind-steering of the thermocline water leakage is essentially reversed, now promoting in combination with the asymmetry in southward Pacific sinking; see Fig. 3. As a result, the wind- land extents essentially control which basin that driven gyre circulation acts to export salt from the becomes the favored site of deep sinking. In the Atlantic to the Pacific, explaining why the Pacific present-day climate, the southern tip of Africa ends sinking state is preferred in this geometry. Interest- near or just north of the zero wind line. This pro- ingly, it has been proposed that the wind pattern motes a westward routing into the Atlantic of contracts equatorward in glacial climates. This warm and relatively saline thermocline water from should give an increased preference for Pacific the Indo–Pacific Basin; a feature known as Agul- sinking, a notion that is partially supported by pa- has leakage. This water feeds the meridional over- leoceanographic data.

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Figure 3 : Simulated circulation in basin geometries which induce a preference for sinking in the ”Atlatic” (a) and the ”Pacific” (b), respectively. Here, the continents terminate at 35 and 25 S (a) and at 50 and 35 S (b). The black lines with arrows depict the flow in the upper 1000 m of the ocean. Red arrows show flow of warm and saline water, whereas the blue ones depict flow of colder and fresher water. The circles above symbolize the location of deep-water formation. In (a) ’’Africa’’ ends equatoward of the zero wind line (the shift between easterly and westerly surface wind, indicated by the grey dashed line). This continental configuration promotes an ”Agulhas”-like transport of saline water from the ”Pacific” to the ”Atlantic”. In this case, the deep sinking is uniquely loca- lized to the ”Atlantic”. In (b), where ’’Africa’’ extends into the westerly winds, the ”Agulhas”-like transport of saline water is curtailed, or even reversed. This promotes a ”Pacific” sinking state, which is shown in (b), but depending on the initial conditions the model can attain equilibrium states with either ”Atlantic” or ”Pacific” sinking in this geometry.

We have also examined how a difference in basin important role and further increase the E-P asym- widths affects the localization of the deep sinking. metry. Here, there are two mechanisms involved. First, the highest evaporation rates are encountered over In summary, the interplay between the wind-driven the swift poleward flowing western boundary cur- circulation, the E-P field, and the basin geometry rents at the edge of subtropics, the Gulf Stream and has the capacity to uniquely localize the northern- the Kuroshio current. The evaporated moisture is hemisphere deep water formation to the Atlantic not returned locally to the ocean, but carried some Ocean. It is primarily the broad features of the distance down-wind before it is precipitated. In a basin geometry, such as the basins widths and the narrow basin, a larger fraction of the evaporation southward extent of the main zonal basin bounda- will be carried over the continental boundary and ries, which matter. Geographical details such as the rain out over the wider basin. As a result, the net Mediterranean Sea, the Atlantic–Arctic connection evaporation per unit area is larger in the narrow and the Bering Strait may also play some role but than in the wide basin. This E-P asymmetry in- are not necessary for localizing the deep water duces a salinification of the narrow basin, which formation to the Atlantic. Interestingly, essentially becomes the preferred location for deep sinking. In all geographical asymmetries in the real world reality, the drainage systems over land also play an appear to favor Atlantic sinking.

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ARCTIC CLIMATE CHANGE Caroline Leck, Michael Tjernström and Rune Grand Graversen

An adequate understanding of the past and the The feedback mechanisms up for debate during the present Arctic climate, and of the processes that last few decades involve: shape it, is a key to projecting the future of this unique region, and the climate impact on society • The so-called “ice-and-snow albedo (reflectivity) including health, social issues and commerce. Over feedback” hypothesis, suggesting that less sea ice the last several decades climate change has been enhances absorption of solar energy at the surface, larger in the Arctic than elsewhere on Earth, and causing more heating and therefore even more sea- since the mid 1960’s the annually averaged near- ice melt (illustrated in Figure 2 upper left panel), surface temperature north of 60°N has increased more than twice as much as the corresponding • The large-scale atmospheric and/or oceanic circu- global average. This is often referred to as the lation that transports energy (heat and water vapor) “Arctic amplification”. One of the most obvious into the Arctic (Figure 2 upper right panel), consequences of this warming, or Arctic amplification is a rapidly diminishing sea ice (Figure 1), • The radiative forcing from greenhouse gases, appearing in all seasons, but most dramatically in cloudiness or cloud albedo and life time (in par- late summer when the sea ice has its annual mini- ticular persistent low-altitude clouds, called stratus mum. It is quite likely that the sea-ice mass, also clouds) illustrated in Figure 2 middle left and right taking the ice thickness into account, is diminish- panels, ing even faster, but thickness is much more difficult to observe. In spite of the considerable effort • The vertical structure of the atmosphere and/or that has been invested in understanding both the ocean, allowing more efficient vertical heat trans- Arctic amplification and its consequence for the port to the surface (the oceanic part illustrated in diminishing ice sea ice, there is not yet a clear Figure 2 lower panel). understanding of the strong feedback mechanisms, or any consensus on their relative importance.

Figure 1 . This schematic picture shows the relationships between annual sea ice minimums in 106 km2 during the period 1977 to 2012. Source: Modified from nasa.gov.

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Figure 2 . A schematic composite illustration of strong feedback mechanisms in the Arctic

One limitation to an understanding of the above from satellites are therefore even more important feedback processes is that the Arctic environment in the Arctic than at lower latitudes. is very hostile to all types of modern instrumentation, and to the people trying to perform experi- Another way of compensating the lack of in-situ ments. An additional limitation is caused by the observations is to make use of reanalysis products, continuously drifting sea-ice, which prevents mea- such as “ERA-Interim” produced by ECMWF surements from being taken at any fixed point for (European Centre for Medium-Range Weather long time periods. After a few years any station Fore-casts). The reanalysis data are often used mounted on the ice will reach the open sea. For instead of “real” observations, as explained in the example, there are very few weather observations box “Reanalysis”. Independent in-situ observations from the Arctic Ocean and almost no information from field experiments, which are not used for the at all on the vertical structure of the atmosphere reanalyses, provide an opportunity to evaluate from regular in-situ observations. Observations models and reanalysis products.

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in the Arctic is not concentrated close to the sur- ReanaReanalysislysis face, as would be expected if the albedo feedback was the primary factor, and also modeling studies A reanalysis data set is based on a combination of that artificially prohibit changes in the albedo sur- observations and a weather prediction model. As the prisingly exhibit Arctic amplification. model is running, it is kept as close to the observations as possible. In areas where observations are few, the reanalysis is mostly determent by the In the summer of 2007 there was a dramatic reduc- model, whereas in areas where observations are tion of the sea-ice cover in the Arctic (as high- plenty and of high quality, the observations have lighted in Figure 1). This event occurred during the strong influence on the reanalysis. An advantage of the reanalyses is that they normally have a International Polar Year (IPY: www.ipy.org) 2007- global coverage. They are widely used within cli- 2008, and caught many scientists by surprise. mate science. ERA-Interim reanalysis data from ECMWF showed that during this summer, the atmospheric energy transport was much larger than usual from The usefulness of the above mentioned methods the Pacific to the area in the Arctic where the most will be exemplified in the below four target ongo- pronounced sea-ice loss was encountered (Grav- ing areas of research within IMI. ersen et al., 2011). This resulted in enhanced energy flux to the surface in this area. This extra Transport of heat and water vapor into the Arc- energy was enough to melt ~1 m of ice. tic A subsequent study examined years with lower and While it is obvious that less snow and ice results in higher September ice extent compared to the linear a lower albedo, and also that a lower albedo will 1979 – 2010 trend. In years with low ice extent in allow more absorption of solar radiation, much of September, it is found that the energy flux from the the Arctic has limited or no sunlight during a large atmosphere to the surface was larger than usual part of the year, especially in winter when warm- already in April (Figure 3). The access of energy ing has been the largest. Although the albedo feed- result in enhanced ice melt over the summer. back contributes the amplified Arctic warming, Hereby a larger area than usual becomes ice free research at MISU have revealed that this feedback which leads to enhanced absorbtion of solar is not playing the main role: the amplified warming

Figure 3 . During years where the Arctic sea-ice extent is smaller than normal by the end of the summer, the energy flux from the atmosphere to the surface is larger than normal already from April. The figure shows anomalies of the net longwave radiation plus the latent and sensible heat fluxes at the surface (red line), Hence the red line indicates the total energy flux from the atmosphere to the surface. Also sown are the net shortwave radiation at the surface (green line), and the anomaly of the sea-ice extent (black line). The anomalies are averaged over an area in the Arctic ocean north of Siberia where the ice retreat is most pronounced. The left axis refers to the energy-flux anomalies, whereas the right axis shows the magnitudes of the ice anomalies. From Kapsch et al., 2013.

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radiation and further melting of the ice in a posi- of results from old and new models in the Coupled tive feedback loop. The enhanced energy-flux to Model Intercomparison Project (CMIP) primarily the surface in April is linked to long wave radia- relied on satellite data. Although some models did tion associated with increase of clouds (Kapsch et show a clear improvement in the Arctic going from al., 2013). The enhanced cloudiness is coupled to older (CMIP3) models to state-of-the-art CMIP5 an increase of the atmospheric humidity transport models, the overall model ensemble performance into the area where the ice reduction is encoun- did not improve. (CMIP3 and CMIP5 laid the tered. The sea-ice extent in September is therefore foundation for results presented in the Intergov- partly dependent on the clouds in April and the ernmental Panel on Climate Change (IPCC) 4th atmospheric transport patterns. and 5th assessment reports, respectively.) Con- cerning clouds, some models even exhibit an in- Satellite studies of Arctic properties verted annual cycle, with more clouds in winter and less in summer, in contrast to observations. Links between atmospheric circulation patterns Insufficient amounts of super-cooled liquid water and clouds, discussed above, were explored using in winter clouds also remain a problem in many the NASA so called “Afternoon Train” (A-Train) models. This is of crucial importance to the surface of satellites; especially cloud observations from energy balance that determines if the ice melts, several sensors. The study illustrated a clear de- since liquid water clouds emit more long-wave pendence of the cloud patterns, especially around radiation than do clouds consisting only of ice Greenland and northern Atlantic, on the leading particles. mode of variability of atmospheric circulation in the Arctic, the Arctic Oscillation (AO). Simply put, Modeling and reanalysis a positive AO-Index indicates a preference for zonal air flow (along a latitude circle), while a Data from (ASCOS; www.ascos.se), in the sum- negative index indicates more north-south air mo- mer of 2008 during the IPY, was used to assess the tions, and this affects the northward transport of quality of global and regional reanalyzes. Figure 4 e.g. water vapor. shows the vertical bias profiles for three variables in ERA-Interim; two versions of the Arctic System Several other satellite studies explored the vertical Reanalysis (ASR) were also included. The bias structure of the Arctic atmosphere. One aspect structure for wind speed and relative humidity is appearing in the Arctic is that absolute humidity very similar also in ASR, with too high wind often increases with height in some layer above the speeds near the surface and too low winds in most surface. This is a condition that rarely occurs else- of the troposphere, but generally small errors in where but is frequent in the Arctic, and implies that relative humidity (except in the lower stratosphere entrainment across the inversion is a moisture where absolute humidity is very low). However, source for the boundary layer rather than a sink. ERA-Interim has a significant warm bias in the This has previously been observed in field studies atmospheric boundary layer (in this case the lowest and most recently over the Arctic pack ice in the 200 m of the atmosphere which behavior is directly summer of 2008 during the Arctic Summer Cloud influenced by its contact with a surface). This bias Ocean Study (ASCOS see below section). Subse- was not present in the ASR. quent to ASCOS we have now also provided a first pan-Arctic perspective from satellite observations. ASR has a much more sophisticated, and complex, The vertical structure and annual cycle of airborne cloud scheme. However, ERA-Interim, with a sim- aerosol particles was also studied. Particle concen- pler scheme, on balance provides better description trations in winter were larger than in summer, re- of the clouds. This paradox – that more advanced ferred to as Arctic Haze; winter particles from cloud models often perform worse in realistic con- pollution were often trapped below a temperature ditions – has been noted before and we speculate inversion at the surface. In summer natural marine that one reason might be sensitivity to aerosol- aerosol particles dominate. cloud interactions. Aerosol particles, including their size, chemical properties and morphology, are With very few other in-situ observations available, important for cloud formation in providing the satellite observations also played an important role nuclei for droplets or ice particles to form. In a in the evaluation of climate models. An evaluation

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Figure 4. Profiles of (gray) median bias profiles with (black) ± one confidence interval at 95% significance of (left) scalar wind speed (ms-1), middle) temperature (°C) and (right) relative humidity (%). Note the logarithmic height scale. simple model an interaction is essentially not al- of low-level clouds, north of 80°. The latest of lowed; all parameters are prescribed but can be these was ASCOS, during the summer of 2008. well tuned. In a more advanced scheme these complex interactions must be correctly modeled which Several unique in-situ observations were taken requires an understanding that to a large extent is during ASCOS. For example, it was for the first lacking for Arctic conditions. time shown unambiguously that biological material from the open water leads in the ice is the same as We also participated in the evaluation of an en- that found in airborne aerosols and in cloud water semble of climate scenario simulations with EC- (Orellana et al., 2011). The connections between Earth; the European climate model, which is partly aerosols and clouds is explained in the box “Get- developed and used within the Bolin Center for ting the clouds right”. Thus, in the summer, ma- Climate Research. It indicated that for the strongest rine life between and under the ice floes must be anthropogenic forcing assumed by IPCC AR5 contributing to cloud formation. summer sea ice will be essentially completely gone, and with it the thick so-called multi-year ice, A mechanism to eject this biological material from slightly after the middle of the present century. the water into the atmosphere was also found (Nor- ris et al., 2011): bubbles that rise in the water col- Arctic Cloud Ocean Study (ASCOS) umn generate droplets as they break the surface. In the open ocean, bubbles form as wind-driven The shown high temporal variability and an enor- waves break and mix air into the water. But such mous number of degrees of freedom, not only in- wave breaking does not happen in the ice-covered situ but also on inter-annual and inter-decadal time Arctic, and yet the smaller bubbles were almost as scales in the Arctic atmosphere, necessitates re- numerous as in the North Sea during storm condi- peating experiments during different years. The tions. below discussed results should be viewed as a direct continuation and development of esearch car- We frequently observed so called mixed-phase ried out in a series of four previous international clouds, where a layer of liquid water that persists ice-breaker expeditions to the high Arctic during for days precipitates ice particles almost constantly the last two decades. The link www.ascos.se gives (an example can be seen to the left in the lower a list of all peer-reviewed articles from the four panel in Figure 5). The lower atmosphere is very expeditions. There has been no other effort than pristine in the summer; sometimes the aerosol con- the four Swedish programs integrating the lower centrations are so low that proper clouds just do atmosphere/upper ocean processes with linkages to not form (Mauritzen et al., 2011); an example marine microorganisms relevant to the formation

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from ASCOS is given in Figure 5. There one can Getting the clouds right see the vertical echo structure as a function of time from a vertically pointing cloud radar for two days, Clouds form when water vapour condenses. But 31 August and 1 September, 2008; the more red, water vapour needs something to condense on – the larger the cloud particles and red coherent ver- tiny airborne aerosol particles known as cloud condensation nuclei (CCN). Typically, CCN are tical streaks indicate precipitating ice. The black about 100 nanometres in diameter. Depending on dots indicate the lower cloud boundary from a laser their properties and heights, clouds can either instrument. One can easily get the impression that warm the surface by triggering a localised there is a solid layer of fog through most of the greenhouse effect or cool it by reflecting solar radiation. night, with clouds from the surface (the black dots) up to about 150 m from the cloud radar. If CCN are scarce, the resulting clouds will contain fewer and larger droplets. Such clouds The photos in the top panels of Figure 5 were taken will reflect little sunlight to space while during this time; at least in the right one there blocking the escape of heat from Earth’s sur- doesn’t seem to be much low clouds or fog around, face, causing it to warm. However, if CCN are plentiful, many fine droplets form and the and looking into the sun no clouds at all ware ap- resultant clouds are better reflectors, which parent. However, the white “fog bow” in both pic- can cool the surface below. tures indicates presence of large spherical objects – droplets – in the air. Thus there is a cloud present, Anthropogenic particles are virtually absent in but so thin that it can almost not be seen by the the summer over the central Arctic, north of latitude 80°N. This “clean” air, with few eye. During this episode the relative humidity was CCN, makes the summer low-level clouds optical- close to 100% all the time, and adding airborne ly thin, with fewer but larger droplets: a heat aerosols, for example from the exhaust of the ice- trap. breaker, a cloud immediately formed. In such conditions, and with the high-albedo surface, cloud But if Arctic warming spurs the activity of microbiota, organic sources of CCN might become formation warms up the surface since long-wave more prominent and lead to more reflecting radiation effects dominate over the reflection of clouds. shortwave radiation back to space.

Figure 5 . At the bottom, time-height section of cloud-radar echo for two days during ASCOS, (left) last of August and first of (right) September, with solid dots indicating lowest cloud base. The photos on top were taken during the night between the two days, and feature very clear cases of so-called fogbow.

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Summary

Many aspects of Arctic climate and climate change remain poorly understood and models are still not well constrained by in-situ and satellite observations. A picture emerges, however, where clouds are very important and where the links between the clouds, the marine biota and the atmospheric circulation is becoming clearer. No stone must be left unturned to improve the understanding of this, using different types of observations and modeling, side by side.

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LIST OF PUBLICATIONS

2009

Achtert, P., W. Birmili, A. Nowak, B. Wehner, A. Wiedensohler, N. Takegawa, Y. Kondo, Y. Miyazaki, M. Hu and T. Zhu, 2009: Hygroscopic growth of tropospheric particle number size distributions over the North China Plain. Journal of Geophysical Research, 114, D00G07–.

Birch, C., I. Brooks, M. Tjernström, S. Milton, P. Earnshaw, O. Persson and S. Söderberg, 2009: The performance of a global and mesoscale model over the central Arctic Ocean during the summer melt season. Journal of Geophysical Research: Atmospheres, 114, D13104–.

Corell, H., J. Nilsson, K. Döös and G. Broström, 2009: Wind sensitivity of the inter-ocean heat exchange. Tellus, 61A(5), 635–653.

Engström, A. and L. Magnusson, 2009: Estimating trajectory uncertainties due to flow dependent errors in the atmospheric analysis. Atmospheric Chemistry and Physics, 9(22), 8857–8867.

Engström, J. E. and C. Leck, 2009: Determination of water-insoluble light absorbing matter in rainwater using polycarbonate membrane filters and photometric detection. Atmospheric Measurement Techniques Discussions, 2, 237–264.

Enmar, L., K. Borenäs, I. Lake and P. Lundberg, 2009: Comments on ”Is the Faroe Bank Channel ower- flow hydraulically controlled”? Journal of Physical Oceanography, 39(6), 1534–1538.

Grand Graversen, R. and M. Wang, 2009: Polar amplification in a coupled climate model with locked albedo. Climate Dynamics, 33(5), 629–643.

Guineva, V., G. Witt, J. Gumbel, M. Khaplanov, R. Werner, J. Hedin, S. Neichev, B. Kirov, L. Bankov, P. Gramatikov, V. Tashev, M. Popov, K. Hauglund, G. Hansen, J. Ilstad and H. Wold, 2009: O-2 density and temperature profiles retrieving from direct solar Lyman-alpha radiation measurements. Geomagnet- ism and Aeronomy, 49(8), 1292–1295.

Gumbel, J. and L. Megner, 2009: Charged meteoric smoke as ice nuclei in the mesosphere. Part 1: A review of basic concepts. Journal of Atmospheric and Solar-Terrestrial Physics, 71(12), 1225–1235.

Gustafsson, Ö., M. Kruså, Z. Zencak, R. J. Sheesley, L. Granat, E. Engström, P. Praveen, P. Rao, C. Leck and H. Rodhe, 2009: Brown clouds over South Asia: Biomass or fossil fuel combustion? Science, 323(23 January), 495–498.

Hedin, J., J. Gumbel, J. Stegman and G. Witt, 2009: Use of O2 airglow for calibrating direct atomic oxy- gen measurements from sounding rockets. Atmospheric Measurement Techniques, 2, 801–812.

Held, A., G. J. Rathbone and J. N. Smith, 2009: A thermal desorption chemical ionization ion trap mass spectrometer for the chemical characterization of ultrafine aerosol particles. Aerosol Science and Tech- nology, 43(3), 264–272.

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Karlsson, B., C. McLandress and T. G. Shepherd, 2009: Inter-hemispheric mesospheric coupling in a comprehensive middle atmosphere model. Journal of Atmospheric and Solar-Terrestrial Physics, 71(3-4), 518–530.

Khosrawi, F., R. Müller, M. H. Proffitt, R. Ruhnke, O. Kirner, P. Jöckel, J.-U. Grooss, J. Urban, D. Mur- tagh and H. Nakajima, 2009: Evaluation of CLaMS, KASIMA and ECHAM5/MESSy1 simulations in the lower stratosphere using observations of Odin/SMR and ILAS/ILAS-II. Atmospheric Chemistry and Physics, 9(15), 5759–5783.

Kjellström, E. and P. Lind, 2009: Changes in the water budget in the Baltic Sea drainage basin in future warmer climates as simulated by the regional climate model RCA3. Boreal and Environmental Research, 14, 114–124.

Körnich, H. and E. Källén, 2009: Climate sensitivity and variability examined in a global climate model, in Multiscale Modeling and Simulation in Science , pp. 299–302. Springer Verlag.

Lind, P. and E. Kjellström, 2009: Water budget in the Baltic Sea drainage basin: Evaluation of simulated fluxes in a regional climate model. Boreal and Environmental Research, 14, 56–67.

Lossow, S., M. Khaplanov, J. Gumbel, J. Stegman, G.Witt, P. Dalin, S. Kirkwood, F. Schmidlin, K. H. Fricke and U. Blum, 2009a: Middle atmospheric water vapour and dynamics in the vicinity of the polar vortex during the Hygrosonde-2 campaign. Atmospheric Chemistry and Physics, 9, 4407–4417.

Lossow, S., J. Urban, H. Schmidt, D. Marsh, J. Gumbel, P. Eriksson and D. Murtagh, 2009b: Wintertime water vapor in the polar upper mesosphere and lower thermosphere: First satellite observations by Odin submillimeter radiometer. Journal of Geophysical Research, 114, D10304–

Lundberg, P., F. Bahrami and M. Zarroug, 2009: A note on the asymptotical alysis of a thermal relaxation oscillator. Zeitschrift für angewandte Mathematik und Mechanik, 89(12), 995–1001.

Magnusson, L., J. Nycander and E. Källén, 2009: Flow-dependent versus flow-independent initial pertur- bations for ensemble forecasting. Tellus. Series A, Dynamic meteorology and oceanography, 61A(2), 194–209.

Megner, L. and J. Gumbel, 2009: Charged meteoric particles as ice nuclei in the mesosphere. Part 2: A feasibility study. Journal of Atmospheric and Solar-Terrestrial Physics, 71(12), 1236–1244.

Megner, L., M. Khaplanov, G. Baumgarten, J. Gumbel, J. Stegman, B. Strelnikov and S. Robertson, 2009: Large mesospheric ice particles at exceptionally high altitudes. Annales Geophysicae, 27, 943–951.

Olofson, K. F. G., E. A. Svensson, G. Witt and J. B. C. Pettersson, 2009: Arctic aerosol and clouds studied by bistatic lidar technique. Journal of Geophysical Research, 114, D18208–.

Paatero, J., P. Vaattovaara, M. Vestenius, O. Meinande, U. Makkonen, R. Kivi, A. Hyvärinen, E. Asmi, M. Tjernström and C. Leck, 2009: Finnish contribution to the Arctic Summer Cloud Ocean Study (ASCOS) expedition, Arctic Ocean 2008. Geophysica, 45, 119–146.

Rapp, M., I. Strelnikova, B. Strelnikov, R. Latteck, G. Baumgarten, Q. Li, L. Megner, J. Gumbel, M. Friedrich, U.-P. Hoppe and S. Robertson, 2009: First in situ measurement of the vertical distribution of ice volume in a mesospheric ice cloud during the ECOMA/MASS rocket-campaign. Annales Geophysi- cae, 27, 755–766.

Robertson, S., M. Horányi, S. Knappmiller, Z. Sternovsky, R. Holzworth, M. Shimogawa, M. Friedrich, K. Torkar, J. Gumbel, L. Megner, G. Baumgarten, R. Latteck, M. Rapp, U.-P. Hoppe and M. E. Hervig,

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2009: Mass analysis of charged aerosol particles in NLC and PMSE during the ECOMA/MASS campaign. Annales Geophysicae, 27, 1213–1232.

Rockström, J., W. Steffen, K. Noone, Å. Persson, F. S. Chapin, E. Lambin,T. M. Lenton, M. Scheffer, C. Folke, H. J. Schellnhuber, B. Nykvist, C. de Wit, T. Hughes, S. van der Leeuw, H. Rodhe, S. Sörlin, R. Constanza, U. Svedin, M. Falkenmark, L. Karlberg, R. W. Corell, V. J. Fabry, J. Hansen, B. Walker, D. L. Liverman, K. Richardson, P. Crutzen and J. A. Foley, 2009a: Planetary boundaries: Exploring the safe operating space for humanity. Ecology & society, 14(2).

Rockström, J., W. Steffen, K. Noone, Å. Persson, F. S. Chapin, E. Lambin, T. M. Lenton, M. Scheffer, C. Folke, H. J. Schellnhuber, B. Nykvist, C. de Wit, T. Hughes, S. van der Leeuw, H. Rodhe, S. Sörlin, R. Constanza,U. Svedin, M. Falkenmark, L. Karlberg, R. W. Corell, V. J. Fabry, J. Hansen, B. Walker, D. L. Liverman, K. Richardson, P. Crutzen and J. A. Foley, 2009b: A safe operating space for humanity. Na- ture, 461(24Sept), 472–475.

Sedlar, J. and R. Hock, 2009: Testing longwave radiation parameterizations under clear and overcast skies at Storglaciären, Sweden. Cryosphere, 3(1), 75–84.

Sedlar, J. and M. Tjernström, 2009: Stratiform cloud-inversion characterization during the Arctic melt season. Boundary-layer Meteorology, 132(3), 455–474.

Strelnikova, I., M. Rapp, B. Strelnikov, G. Baumgarten, A. Brattli, K. Svenes, U.-P. Hoppe, M. Friedrich, J. Gumbel and B. P.Williams, 2009: Measurements of meteor smoke particles during the ECOMA-2006 campaign. 2: Results. Journal of Atmospheric and Solar-Terrestrial Physics, 71(3-4), 486–496.

Sundqvist, H. S., Q. Zhang, A. Moberg, K. Holmgren, H. Körnich and J. Nilsson, 2009: Northern high- latitude climate change between the mid and late Holocene. Part 1: Proxy data evidence. Climate of the Past Discussions, 5(4), 1819–1852.

Svensson, G. and A. Holtslag, 2009: Analysis of model results for the turning of the wind and related momentum fluxes in the stable boundary layer. Boundary-layer Meteorology, 132(2), 261–277.

Tjernström, M., B. B. Balsley, G. Svensson and C. J. Nappo, 2009: The effects of critical layers on residual layer turbulence. Journal of Atmospheric Sciences, 66(2), 468–480.

Tjernström, M. and R. G. Graversen, 2009: The vertical structure of the lower Arctic troposphere analysed from observations and the ERA-40 reanalysis. Quarterly Journal of the Royal Meteorological Socie- ty, 135(639), 431–443.

Tjernström, M. and T. Mauritsen, 2009: Mesoscale variability in the summer Arctic boundary layer. Boundary-layer Meteorology, 130(3), 383–406.

Wang, C., D. Kim, A. M. L. Ekman, M. C. Barth and P. J. Rasch, 2009: Impact of anthropogenic aerosols on Indian summer monsoon. Geophysical Research Letters, 36, L21704–.

Zhang, Q., H. Sundqvist, A. Moberg, K. Holmgren, H. Körnich and J. Nilsson, 2009: Northern high- latitude climate change between the mid and late Holocene. Part 2: Model-data comparisons. Climate of the Past Discussions, 5(3), 1659–1696.

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2010

Bahrami, F., J. Nycander and R. Alikhani, 2010: Existence of energy maximizing vortices in a three- dimensional quasigeostrophic shear flow with bounded height. Nonlinear Analysis, 11(3), 1589–1599.

Bender, F., A. Ekman and H. Rodhe, 2010: Response to the eruption of Mount Pinatubo in relation to climate sensitivity in the CMIP3 models. Climate Dynamics, 35(5), 875–886.

Brodeau, L., B. Barnier, A.M. Treguier, T. Penduff and S. Gulev, 2010: An ERA40-based atmospheric forcing for global ocean circulation models. Ocean Modelling, 31 (3-4), 88-104, 2010.

Engström, A. and A. M. Ekman, 2010: Impact of meteorological factors on the correlation between aerosol optical depth and cloud fraction. Geophysical Research Letters, 37, L18814–.

Gao, Q., M. Araia, C. Leck and Å. Emmer, 2010: Characterization of exopolysaccharidesin marine collo- ids by capillary electrophoresis with indirect UV detection. Analytica Chimica Acta, 662(2), 193–199.

Gattinger, R. L., A. Egeland, A. E. Bourassa, N. D. Lloyd, D. A. Degenstein, J. Stegman and E. J. Lle- wellyn, 2010: H Balmer lines in terrestrial aurora: Historical record and new observations by OSIRIS on Odin. Journal of Geophysical Research, 115, A09306–.

Granat, L., E. Engström, S. Praveen and H. Rodhe, 2010: Light absorbing material (”soot”) in rainwater and in aerosol particles in the Maldives Journal of Geophysical Research, 115, D16307–.

Hazeleger, W., C. Severijns, T. Semmler, S. E. Stefanescu, S. Yang, X. Wang, K. Wyser, J. S. Baldasano, G. Balsamo, P. Bechtold, R. Bintanja, R. Caballero, E. Dutra, A. M. L. Ekman, J. H. Christensen, B. van den Hurk, P. Jimenez, C. Jones, P. Kållberg, T. Koenigk, R. McGrath, P. M. A. Miranda, F. Molteni, T. van Noije, T. Palmer, T. Rodriguez Camino, T. Schmith, F. Selten, T. Storelvmo, A. Sterl, H. Tapamo, P. Viterbo and U. Wilén, 2010: EC-Earth: a seamless earth system prediction approach inaction. Bulletin of the American Meteorological Society, 91(4), 1357–1363.

Hodson, A., T. J. Roberts, A.-C. Engvall, K. Holmen and P. Mumford, 2010: Glacier ecosystem response to episodic nitrogen enrichment in Svalbard, European High Arctic. Biogeochemistry, 98(03-jan), 171– 184.

Jakobsson, M., J. Nilsson, M. O’Regan, J. Backman, L. Löwemark, J. A. Dowdeswell, L. Mayer, L. Po- lyak, F. Colleoni, L. G. Anderson, G. Björk, D. Darby, B. Eriksson, D. Hanslik, B. Hell, C. Marcussen, E. Sellén and T. Wallin, 2010: An Arctic Ocean ice shelf during MIS 6 constrained by new geophysical and geological data. Quaternary Science Reviews, 29(25-26), 3505–3517.

Karlsson, J., G. Svensson, S. Cardoso and J. Teixeira, 2010: Subtropical cloud regime transitions: boundary layer depth and cloud-top height evolution. Journal of Applied Meteorology and Climatology, 49(9), 1845–1858.

Khosrawi, F., J. Ström, A. Minikin and R. Krejci, 2010: Particle formation in the Arctic free troposphere during the ASTAR 2004 campaign: A case study on the influence of vertical motion on the binary homogeneous nucleation of H2SO4/H2O. Atmospheric Chemistry and Physics,10, 1105–1120.

Kjellström, E., J. Brandefelt, J.-O. Näslund, B. Smith, G. Strandberg, A. H. L. Voelker, B. Wohlfarth, 2010: Simulated climate conditions in Europe during the Marine Isotope Stage 3 stadial. Boreas,39 (2) 436-456.

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Körnich, H. and E. Becker, 2010: A simple model for the interhemispheric coupling of the middle atmosphere circulation. Advances in Space Research, 45(5), 661–668.

Kumar, V., G. Svensson, A. A. M. Holtslag, C. Meneveau and M. B. Parlange, 2010: Impact of surface flux formulations and geostrophic forcing on large eddy simulations of diurnal atmospheric boundary layer flow. Journal of Applied Meteorology and Climatology, 49(7), 1496–1516.

Leck, C. and E. K. Bigg, 2010: New particle formation of marine biologi calorigin. Aerosol Science and Technology, 44(7), 570–577.

Leck, C., and E. K. Bigg, 2010, Erratum: New particle formation of marine biological origin (Aerosol Science and Technology 44:7 (570-577)), Aerosol Science and Technology, 44 (10) 917.

Li, X., T. Hede, Y. Tu, C. Leck and H. Ågren, 2010: Surface-active cispinonic acid in atmospheric droplets: a molecular dynamics study. Journal of Physical Chemistry Letters, 1(4), 769–773.

Liakka, J. and J. Nilsson, 2010: The impact of topographically forced stationary waves on local ice-sheet climate. Journal of Glaciology, 56(197), 534–544.

Lohmann, U., L. Rotstayn, T. Storelvmo, A. Jones, S. Menon, J. Quaas, A. M. L. Ekman, D. Koch and R. Ruedy, 2010: Total aerosol effect: radiative forcing or radiative flux perturbation? Atmospheric Chemi- stry and Physics, 10(7), 3235–3246.

Lundén, J., G. Svensson, A. Wisthaler, M. Tjernström, A. Hansel and C. Leck, 2010: The vertical distribution of atmospheric DMS in the high Arctic summer. Tellus. Series B, Chemical and physical meteorology, 62(3), 160–171.

Megner, L., 2010: Minimal impact of condensation nuclei characteristics on observable mesospheric ice properties. Journal of Atmospheric and Solar-Terrestrial Physics, doi: 10.1016/j.jastp.2010.08.006, 2184- 2191.

Moberg, A., K. Holmgren, H. Renssen, H. Sundqvist and Q. Zhang, 2010: Preface ”Holocene climate variability over Scandinavia – A special issue originating from a workshop organized by the Bert Bolin Centre for Climate Research”. Climate of the Past, 6(5), 719–721.

Nilsson, J. and G. Walin, 2010: Salinity-dominated thermohaline circulation in sill basins: can two stable equilibria exist? Tellus. Series A, Dynamic meteorology and oceanography, 62(2), 123–133.

Nycander, J., 2010: Horizontal convection with a non-linear equation of state: generalization of a theorem of Paparella and Young. Tellus. Series A, Dynamic meteorology and oceanography, 62(2), 134–137.

Penduff, T., M. Juza, L. Brodeau, G. C. Smith, B. Barnier, J.-M. Molines, A.-M. Treguier and G. Madec, 2010: Impact of global ocean model resolution on sea-level variability with emphasis on interannual time scales. Ocean Science, 6, 269-284.

Rapp, M., I. Strelnikova, B. Strelnikov, P. Hoffmann, M. Friedrich, J. Gumbel, L. Megner, U. -P. Hoppe, S. Robertson, S. Knappmiller, M. Wolff and D. R. Marsh, 2010: Rocket-borne in situ measurements of meteor smoke: Charging properties and implications for seasonal variation. Journal of Geophysical Re- search, 115, D00I16–.

Schwartz, S. E., R. J. Charlson, R. A. Kahn, J. A. Ogren and H. Rodhe, 2010: Why hasn’t Earth warmed as much as expected? Journal of Climate, 23(10), 2453–2464.

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Sturm, C., Q. Zhang and D. Noone, 2010: An introduction to stable water isotopes in climate models: benefits of forward proxy modelling for paleo climatology. Climate of the Past, 6, 115–129.

Sundqvist, H. S., Q. Zhang, A. Moberg, K. Holmgren, H. Körnich, J. Nilsson and G. Brattström, 2010: Climate change between the mid and late Holocene in the northern high latitudes. Part I: Survey of temperature and precipitation proxy data. Climate of the Past, 6, 591–608.

Syed, F. S., F. Giorgi, J. S. Pal and K. Keay, 2010a: Regional climate model simulation of winter climate over Central-Southwest Asia, with emphasis on NAO and ENSO effects. International Journal of Clima- tology, 30(2), 220–235.

Syed, F. S., J. H. Yoo, H. Körnich and F. Kucharski, 2010b: Are intra seasonal summer rainfall events micro monsoon onsets over the western edge of the South-Asian monsoon? Atmospheric research, 98(2- 4), 341–346.

Thompson, B., J. Nilsson, J. Nycander, M. Jakobsson and K. Döös, 2010: Ventilation of the Miocene Arctic Ocean: An idealized model study. Paleoceanography, 25, PA4216.

Zarroug, M., J. Nycander and K. Döös, 2010: Energetics of tidally generated internal waves. Tellus. Se- ries A, Dynamic meteorology and oceanography, 62(1), 71–79.

Zhang, Q., H. Sundqvist, A. Moberg, H. Körnich, J. Nilsson and K. Holmgren, 2010: Climate change between the mid and late Holocene in northern high latitudes: Part 2: Model-data comparisons. Climate of the Past, 6, 609–626.

2011

Achtert, P., F. Khosrawi, U. Blum and K. H. Fricke, 2011: Investigation of polar stratospheric clouds in January 2008 by means of ground-based and spaceborne lidar measurements and microphysical box model simulations. Journal of Geophysical Research, 116, D07201–.

Almroth Rosell, E., K. Eilola, R. Hordoir, H. E. M. Meier, and P. O. J. Hall, 2011: Transport of fresh and resuspended particulate organic material in the Baltic Sea - a model study. Journal of Marine Systems, 87, 1-12.

Axelsson, P., M. Tjernström, S. Söderberg and G. Svensson, 2011: An ensemble of Arctic simulations of the AOE-2001 field experiment. Atmoshere, 2(2), 146–170.

Bender, F. A. M., 2011: Planetary albedo in strongly forced climate, as simulated by the CMIP3 models. Theoretical and Applied Climatology, 105, 529–535.

Bender, F. A. M., R. J. Charlson, A. M. L. Ekman and L. V. Leahy, 2011: Quantification of monthly mean regional-scale albedo of marine stratiform clouds in satellite observations and GCMs. Journal of Applied Meteorology and Climatology, 50(10), 2139–2148.

Bengtsson, L., H. Körnich, E. Källén and G. Svensson, 2011: Large-scale dynamical response to subgrid- scale organization provided by cellular automata. Journal of Atmospheric Sciences, 68(12), 3132–3144.

Bocquet, F., B. Balsley, M. Tjernström and G. Svensson, 2011: Comparing estimates of turbulence based on near-surface measurements in the nocturnal stable boundary layer. Boundary-layer Meteorology, 138(1), 43–60.

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Caballero, R. and P. Lynch, 2011: Climate modelling and deep-time climate change, in Climate Change, Ecology and Systematics. , pp. 44–66. Cambridge University Press.

Chang, R. Y. W., C. Leck, M. Graus, M. Mueller, J. Paatero, J. F. Burkhart, A. Stohl, L. H. Orr, K. Hay- den, S. M. Li, A. Hansel, M. Tjernström, W. R. Leaitch and J. P. D. Abbatt, 2011: Aerosol composition and sources in the central Arctic Ocean during ASCOS. Atmospheric Chemistry and Physics, 11(20), 10619–10636.

Colleoni, F., J. Liakka, G. Krinner, M. Jakobsson, S. Masina and V. Peyaud, 2011: The sensitivity of the Late Saalian (140 ka) and LGM (21 ka) Eurasian ice sheets to sea surface conditions. Climate Dynamics, 37(3-4), 531–553.

Coz Diego, E. and C. Leck, 2011: Morphology and state of mixture of atmospheric soot aggregates during the winter season over Southern Asia - quantitative approach. Tellus. Series B, Chemical and physical meteorology, 63(1), 107–116.

Das, R., L. Granat, C. Leck, P. S. Praveen and H. Rodhe, 2011: Chemical composition of rainwater at Maldives Climate Observatory at Hanimaadhoo (MCOH). Atmospheric Chemistry and Physics, 11(8), 3743–3755.

Devasthale, A., J. Sedlar and M. Tjernström, 2011a: Characteristics of water-vapour inversions observed over the Arctic by Atmospheric Infrared Sounder (AIRS) and radiosondes. Atmospheric Chemistry and Physics, 11(18), 9813–9823.

Devasthale, A., M. Tjernström, K.-G. Karlsson, M. A. Thomas, C. Jones, J. Sedlar and A. H. Omar, 2011b: The vertical distribution of thin features over the Arctic analysed from CALIPSO observations. Part I: Optically thin clouds. Tellus, 63B(1), 77–85.

Devasthale, A., M. Tjernström and A. H. Omar, 2011c: The vertical distribution of thin features over the Arctic analysed from CALIPSO observations. Part II: Aerosols. Tellus, 63B(1), 86–95.

Döös, K. and J. Nilsson, 2011: Analysis of the meridional energy transport by atmospheric overturning circulations. Journal of Atmospheric Sciences, 68(8), 1806–1820.

Döös, K., V. Rupolo and L. Brodeau, 2011: Dispersion of surface drifters and model-simulated trajectories. Ocean Modelling, 39(3-4), 301–310.

Ekman, A. M. L., A. Engström and A. Söderberg, 2011: Impact of two-way aerosol-cloud interaction and changes in aerosol size distribution on simulated aerosol-induced deep convective cloud sensitivity. Jour- nal of Atmospheric Sciences, 68(4), 685–698.

Enell, C.-F., J. Hedin, J. Stegman, G. Witt, M. Friedrich, W. Singer, G. Baumgarten, B. Kaifler, U.-P. Hoppe, B. Gustavsson, U. Brandström, M. Khaplanov, A. Kero, T. Ulich and E. Turunen, 2011: The Ho- tel Payload 2 campaign: Overview of NO, O and electron density measurements in the upper mesosphere and lower thermosphere. Journal of Atmospheric and Solar-Terrestrial Physics, 73(14-15), 2228–2236.

Engström, J. E. and C. Leck, 2011: Reducing uncertainties associated with filter-based optical measurements of light absorbing carbon particles with chemical information. Atmospheric Measurement Tech- niques, 4(8), 1553–1566.

Espy, P. J., S. Ochoa Fernandez, P. Forkman, D. Murtagh and J. Stegman, 2011: The role of the QBO in the inter-hemispheric coupling of summer mesospheric temperatures. Atmospheric Chemistry and Phys- ics, 11(2), 495–502.

48 BIENNIAL REPORT 2011 – 2012

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Gabriel, A., H. Körnich, S. Lossow, J. Urban and D. Murtagh, 2011: Zonal asymmetries in middle atmospheric ozone and water vapour derived from Odin satellite data 2001–2010. Atmospheric Chemistry and Physics, 11, 9865–9885.

Gao, Q., U. Nilsson, L. L. Ilag and C. Leck, 2011: Monosaccharide compositional analysis of marine polysaccharides by hydrophilic interaction liquid chromatography-tandem mass spectrometry. Analytical and Bioanalytical Chemistry, 399(7), 2517–2529.

Goldner, A., M. Huber, N. Diffenbaugh and R. Caballero, 2011: Implications of the permanent El Nino teleconnection ”blueprint” for past global and North American hydroclimatology. Climate of the Past, 7, 723–743.

Graversen, R. G., T. Mauritsen, S. Drijfhout, M. Tjernström and S. Mårtensson, 2011: Warm winds from the Pacific caused extensive Arctic sea-ice melt in summer 2007. Climate Dynamics, 36(11-12), 2103– 2112.

Gumbel, J., H. Körnich, S. M. Bailey, F. J. Lubken and R. Morris, 2011: Special issue on layered pheno- mena in the mesopause region Foreword. Journal of Atmospheric and Solar-Terrestrial Physics, 73(14- 15), 2045– 2048.

Hannachi, A., A. Awad and K. Ammar, 2011a: Climatology and classification of Spring Saharan cyclones. Journal of Atmospheric Sciences, 37, 473–491.

Hannachi, A., D. Mitchell, L. Gray and A. Charlton-Perez, 2011b: On the use of geometric moments to examine the continuum of sudden stratospheric warmings. Journal of Atmospheric Sciences, 68(3), 657– 674.

Hede, T., X. Li, C. Leck, Y. Tu and H. Ågren, 2011: Model HULIS compounds in nanoaerosol clusters - investigations of surface tension and aggregate formation using molecular dynamics simulations. Atmos- pheric Chemistry and Physics, 11(13), 6549–6557.

Hedin, J. and J. Gumbel, 2011: The global mesospheric sodium layer observed by Odin/OSIRIS in 2004- 2009. Journal of Atmospheric and Solar- Terrestrial Physics, 73(14-15), 2221–2227.

Held, A., I. M. Brooks, C. Leck and M. Tjernström, 2011a: On the potential contribution of open lead particle emissions to the central Arctic aerosol concentration. Atmospheric Chemistry and Physics, 11(7), 3093–3105.

Held, A., D. A. Orsini, P. Vaattovaara, M. Tjernström and C. Leck, 2011b: Near-surface profiles of aerosol number concentration and temperature over the Arctic Ocean. Atmospheric Measurement Techniques, 4(8), 1603–1616.

Huber, M. and R. Caballero, 2011: The early Eocene equable climate problem revisited. Climate of the Past, 7(2), 603–633.

Hultgren, K., H. Körnich, J. Gumbel, M. Gerding, P. Hoffmann, S. Lossow and L. Megner, 2011: What caused the exceptional mid-latitudinal Noctilucent Cloud event in July 2009? Journal of Atmospheric and Solar- Terrestrial Physics, 73(14-15), 2125–2131.

Jönsson, B. F., K. Döös, K. Myrberg and P. A. Lundberg, 2011: A Lagrangian-trajectory study of a gradually mixed estuary. Continental Shelf Research, 31(17), 1811–1817.

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Karl, M., A. Gross, L. Pirjola and C. Leck, 2011: A new flexible multicomponent model for the study of aerosol dynamics in the marine boundary layer. Tellus. Series B, Chemical and physical meteorology, 63(5), 1001–1025.

Karlsson, J. and G. Svensson, 2011: The simulation of Arctic clouds and their influence on the winter surface temperature in present-day climate in the CMIP3 multi-model dataset. Climate Dynamics, 36(3- 4), 623–635.

Khosrawi, F., J. Urban, M. C. Pitts, P. Voelger, P. Achtert, M. Kaphlanov, M. L. Santee, G. L. Manney, D. Murtagh and K. H. Fricke, 2011: Denitrification and polar stratospheric cloud formation during the Arctic winter 2009/2010. Atmospheric Chemistry and Physics, 11(16), 8471–8487.

Knappmiller, S., M. Rapp, S. Robertson and J. Gumbel, 2011: Charging of meteoric smoke and ice particles in the mesosphere including photoemission and photodetachment rates. Journal of Atmospheric and Solar-Terrestrial Physics, 73(14-15), 2212–2220.

Li, X., T. Hede, Y. Tu, C. Leck and H. Ågren, 2011a: Amino acids in atmospheric droplets: perturbation of surface tension and critical supersaturation predicted by computer simulations. Atmospheric Chemistry and Physics Discussions, 11, 30919–30947.

Li, X., T. Hede, Y. Tu, C. Leck and H. Ågren, 2011b: Glycine in aerosol water droplets: a critical assessment of Köhler theory by predicting surface tension from molecular dynamics simulations. Atmospheric Chemistry and Physics, 11(2), 519–527.

Martin, M., R. Y.-W. Chang, B. Sierau, S. Sjögren, E. Swietlicki, J. P. D. Abbatt, C. Leck and U. Loh- mann, 2011: Cloud condensation nuclei closure study on summer arctic aerosol. Atmospheric Chemistry and Physics, 11(22), 11335–11350.

Mauritsen, T., J. Sedlar, M. Tjernström, C. Leck, M. Martin, M. Shupe, S. Sjogren, B. Sierau, P. O. G. Persson, I. M. Brooks and E. Swietlicki, 2011: An Arctic CCN-limited cloud-aerosol regime. Atmospher- ic Chemistry and Physics, 11(1), 165–173.

Meier, M., K. Eilola and E. Almroth, 2011a: Climate-related changes in marine ecosystems simulated with a 3-dimensional coupled physicalbiogeochemical model of the Baltic Sea. Climate Research, 48(1), 31–55.

Meier, M., A. Höglund, R. Döscher, H. Andersson, U. Löptien and E. Kjellström, 2011b: Quality assessment of atmospheric surface fields over the Baltic Sea from an ensemble of regional climate model simulations with respect to ocean dynamics. Oceanologia, 53(1-TI), 193–227.

Mitchell, J. L., M. Adamkovics, R. Caballero and E. P. Turtle, 2011: Locally enhanced precipitation organized by planetary-scale waves on Titan. Nature Geoscience, 4(9), 589–592.

Mueller, T., J. S. Henzing, G. de Leeuw, A. Wiedensohler, A. Alastuey, H. Angelov, M. Bizjak, M. C. Coen, J. E. Engström, C. Gruening, R. Hillamo, A. Hoffer, K. Imre, P. Ivanow, G. Jennings, J. Y. Sun, N. Kalivitis, H. Karlsson, M. Komppula, P. Laj, S.-M. Li, C. Lunder, A. Marinoni, S. M. dos Santos, M. Moerman, A. Nowak, J. A. Ogren, A. Petzold, J. M. Pichon, S. Rodriquez, S. Sharma, P. J. Sheridan, K. Teinila, T. Tuch, M. Viana, A. Virkkula, E. Weingartner, R. Wilhelm and Y. Q. Wang, 2011: Characteri- zation and intercomparison of aerosol absorption photometers: result of two intercomparison workshops. Atmospheric Measurement Techniques, 4(2), 245–268.

Norris, S. J., I. M. Brooks, G. de Leeuw, A. Sirevaag, C. Leck, B. J. Brooks, C. E. Birch and M. Tjernström, 2011: Measurements of bubble size spectra within leads in the Arctic summer pack ice. Ocean Science, 7(1), 129–139.

50 BIENNIAL REPORT 2011 – 2012

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Nycander, J., 2011: Energy conversion, mixing energy, and neutral surfaces with a nonlinear equation of state. Journal of Physical Oceanography, 41(1), 28–41.

Orellana, M. V., P. A. Matrai, C. Leck, C. D. Rauschenberg, A. M. Lee and E. Coz, 2011: Marine micro- gels as a source of cloud condensation nuclei in the high Arctic. Proceedings of the National Academy of Sciences of the United States of America, 108(33), 13612–13617.

Partridge, D. G., J. A. Vrugt, P. Tunved, A. M. L. Ekman, D. Gorea and A. Sorooshian, 2011: Inverse modeling of cloud-aerosol interactions: Part 1: Detailed response surface analysis. Atmospheric Chemi- stry and Physics, 11(14), 7269–7287.

Pautet, P. D., J. Stegman, C. M. Wrasse, K. Nielsen, H. Takahashi, M. J. Taylor, K. W. Hoppel and S. D. Eckermann, 2011: Analysis of gravity waves structures visible in noctilucent cloud images. Journal of Atmospheric and Solar-Terrestrial Physics, 73(14-15), 2082–2090.

Rivera-Monroy, V. H., R. R. Twilley, J. Ernesto Mancera-Pineda, C. J. Madden, A. Alcantara-Eguren, E. B. Moser, B. F. Jonsson, E. Castaneda- Moya, O. Casas-Monroy, P. Reyes-Forero and J. Restrepo, 2011: Salinity and chlorophyll a as performance measures to rehabilitate a mangrove dominated deltaic coastal region: the Cienaga Grande de Santa Marta- Pajarales lagoon complex, Colombia. Estuaries and Coasts, 34(1), 1–19.

Sedlar, J., M. Tjernström, T. Mauritsen, M. Shupe, I. Brooks, P. Persson, C. Birch, C. Leck, A. Sirevaag and M. Nicolaus, 2011: A transitioning Arctic surface energy budget: the impacts of solar zenith angle, surface albedo and cloud radiative forcing. Climate Dynamics, 37(7-8), 1643–1660.

Sigray, P. and M. H. Andersson, 2011: Particle motion measured at an operational wind turbine in relation to hearing sensitivity in fish. Journal of Acoustical Society of America, 130(1), 200–207.

Sirevaag, A., S. de la Rosa, I. Fer, M. Nicolaus, M. Tjernström and M. G. McPhee, 2011: Mixing, heat fluxes and heat content evolution of the Arctic Ocean mixed layer. Ocean Science, 7(3), 335–349.

Soomere, T., N. Delpeche, B. Viikmaee, E. Quak, H. E. M. Meier and K. Döös, 2011: Patterns of current- induced transport in the surface layer of the Gulf of Finland. Boreal Environment Research, 16, 49–63.

Strandberg, G., J. Brandefelt, E. Kjellström, B. Smith, 2011. High resolution regional simulation of Last Glacial Maximum climate in Europe. Tellus, 63A(1), 107-125.

Struthers, H., A. Ekman, P. Glantz, T. Iversen, A. Kirkevag, M. Mårtensson, O. Seland and D. Nilsson, 2011: The effect of sea ice loss on sea salt aerosol concentrations and the radiative balance in the Arctic. Atmospheric Chemistry and Physics, 11(7), 3459–3477.

Svensson, G., A. A. M. Holtslag, V. Kumar, T. Mauritsen, G. J. Steeneveld, W. M. Angevine, E. Bazile, A. Beljaars, E. I. F. de Bruijn, A. Cheng, L. Conangla, J. Cuxart, M. Ek, M. J. Falk, F. Freedman, H. Ki- tagawa, V. E. Larson, A. Lock, J. Mailhot, V. Masson, S. Park, J. Pleim, S. Söderberg, W. Weng and M. Zampieri, 2011: Evaluation of the diurnal cycle in the atmospheric boundary layer over land as represented by a variety of single-column models: the second GABLS experiment. Boundary-layer Mete- orology, 140(2), 177–206.

Svensson, G. and J. Karlsson, 2011: On the Arctic wintertime climate in global climate models. Journal of Climate, 24(22), 5757–5771.

Teixeira, J., S. Cardoso, M. Bonazzola, J. Cole, A. DelGenio, C. DeMott, C. Franklin, C. Hannay, C. Jakob, Y. Jiao, J. Karlsson, H. Kitagawa, M. Koehler, A. Kuwano-Yoshida, C. LeDrian, J. Li, A. Lock, M. J. Miller, P. Marquet, J. Martins, C. R. Mechoso, E. V. Meijgaard, I. Meinke, P. M. A. Miranda, D.

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Mironov, R. Neggers, H. L. Pan, D. A. Randall, P. J. Rasch, B. Rockel, W. B. Rossow, B. Ritter, A. P. Siebesma, P. M. M. Soares, F. J. Turk, P. A. Vaillancourt, A. Von Engeln and M. Zhao, 2011: Tropical and subtropical cloud transitions in weather and climate prediction models: The GCSS/WGNE Pacific cross-section intercomparison (GPCI). Journal of Climate, 24(20), 5223–5256.

Unkel, S., A. Hannachi, N. T. Trendafilov and I. T. Jolliffe, 2011: Independent component analysis for three-way data with an application from atmospheric science. Journal of Agricultural Biological and En- vironmental Statistics, 16(3), 319–338.

Witt, G., 2011: Size and shape of ice grains in the mesopause region. International Journal of Remote Sensing, 32(11), 3029–3041.

2012

Achtert, P., M. Karlsson Andersson, F. Khosrawi and J. Gumbel, 2012: On the linkage between tropospheric and Polar Stratospheric clouds in the Arctic as observed by space-borne lidar. Atmospheric Chemi- stry and Physics, 12(8), 3791–3798.

Baron, P., D. Murtagh, J. Urban, S. Sagawa, H. Ochiai, H. Koernich, F. Khosrawi, K. Kikuchi, S. Mizo- buchi, K. Sagi, Y. Kasai and M. Yasui, 2012: Observation of horizontal winds in the middle-atmosphere between 30_S and 55_N during the northern winter 2009–2010. Atmospheric Chemistry and Physics Discussions, 12, 32473–32513.

Bender, F. A. M., 2012: Aerosol forcing: Rapporteur’s report and summary. Surveys in Geophysics, 33(3–4), 693–700.

Bender, F. A. M., V. Ramanathan and G. Tselioudis, 2012: Changes in extratropical storm track cloudiness 1983-2008: Observational support for a poleward shift. Climate Dynamics, 38(9–10), 2037–2053.

Bengtsson, L., S. Tijm, F. Vána and G. Svensson, 2012: Impact of flow dependent horizontal diffusion on resolved convection in AROME. Journal of Applied Meteorology and Climatology, 51(1), 54–67.

Benze, S., C. E. Randall, B. Karlsson, V. L. Harvey, M. T. DeLand, G. E. Thomas and E. P. Shettle, 2012: On the onset of polar mesospheric cloud seasons as observed by SBUV. Journal of Geophysical Research, 117, D07104–.

Birch, C. E., I. M. Brooks, M. Tjernström, M. D. Shupe, T. Mauritsen, J. Sedlar, A. P. Lock, P. Earnshaw, P. O. G. Persson, S. F. Milton and C. Leck, 2012: Modelling atmospheric structure, cloud and their response to CCN in the central Arctic: ASCOS case studies. Atmospheric Chemistry and Physics, 12(7), 3419–3435.

Bromley, T., W. Allan, R. Martin, S. E. M. Fletcher, D. C. Lowe, H. Struthers and R. Moss, 2012: Ship- board measurements and modeling of the distribution of CH4 and (CH4)-C-13 in the western Pacific. Journal of Geophysical Research, 117, D04307–.

Caballero, R. and J. Hanley, 2012: Mid latitude eddies, storm-track diffusivity, and poleward moisture transport in warm climates. Journal of Atmospheric Sciences, 69(11), 3237–3250.

Caron, L.-P. and C. G. Jones, 2012: Understanding and simulating the link between African easterly waves and Atlantic tropical cyclones using a regional climate model: the role of domain size and lateral boundary conditions. Climate Dynamics, 39(1-2), 113–135.

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LIST OF PUBLICATIONS

Chafik, L., 2012: The response of the circulation in the Faroe-Shetland channel to the North Atlantic Os- cillation. Tellus. Series A, Dynamic meteorology and oceanography, 64, 18423–.

Corell, H., P.-O. Moksnes, A. Engqvist, K. Döös and P. R. Jonsson, 2012: Depth distribution of larvae critically affects their dispersal and the efficiency of marine protected areas. Marine Ecology Progress Series, 467, 29.

Cronin, T. M., G. S. Dwyer, J. Farmer, H. A. Bauch, R. F. Spielhagen, M. Jakobsson, J. Nilsson, J. Briggs, W. M. and A. Stepanova, 2012: Deep Arctic Ocean warming during the last glacial cycle. Nature Geoscience, 5(9), 631–634.

Devasthale, A., M. Tjernström, M. Caian, M. A. Thomas, B. H. Kahn and E. J. Fetzer, 2012: Influence of the Arctic oscillation on the vertical distribution of clouds as observed by the a train constellation of satellites. Atmospheric Chemistry and Physics, 12(21), 10535–10544.

Döös, K., J. Nilsson, J. Nycander, L. Brodeau and M. Ballarotta, 2012: The world ocean thermohaline circulation. Journal of Physical Oceanography, 42(9), 1445–1460.

Ekman, A. M. L., M. Hermann, P. Gross, J. Heintzenberg, D. Kim and C. Wang, 2012: Sub-micrometer aerosol particles in the upper troposphere/ lowermost stratosphere as measured by CARIBIC and modeled using the MIT-CAM3 global climate model. Journal of Geophysical Research, 117, D11202–.

Gao, Q., C. Leck, C. Rauschenberg and P. A. Matrai, 2012: On the chemical dynamics of extracellular polysaccharides in the high Arctic surface microlayer. Ocean Science, 8(4), 401–418.

Gattinger, R. L., I. C. McDade, A. L. Broadfoot, W. F. J. Evans, J. Stegman and E. J. Llewellyn, 2012: Vibrational populations of near-ultraviolet O-2 band systems in the night airglow. Canadian Journal of Physics, 90(8), 741–751.

Hanley, J. and R. Caballero, 2012a: Objective identification and tracking of multi-centre cyclones in the ERA-Interim reanalysis dataset. Quarterly Journal of the Royal Meteorological Society, 138(664), 612– 625.

Hanley, J. and R. Caballero, 2012b: The role of large-scale atmospheric flow and Rossby wave breaking in the evolution of extreme windstorms over Europe. Geophysical Research Letters, 39, L21708–.

Hannachi, A., T. Woollings and K. Fraedrich, 2012: The North Atlantic jet stream: a look at preferred positions, paths and transitions. Quarterly Journal of the Royal Meteorological Society, 138(665), 862– 877.

Hedin, J., M. Rapp, M. Khaplanov, J. Stegman and G. Witt, 2012: Observations of NO in the upper mesosphere and lower thermosphere during ECOMA 2010. Annales Geophysicae, 30, 1611–1621.

Heintzenberg, J. and C. Leck, 2012: The summer aerosol in the Central Arctic 1991-2008: did it change or not? Atmospheric Chemistry And Physics, 12(9), 3969–3983.

Hellen, H., C. Leck, J. Paatero, A. Virkkula and H. Hakola, 2012: Summer concentrations of NMHCs in ambient air of the Arctic and Antarctic. Boreal Environment Research, 17(5), 385–397.

Jacobi, M. N., C. Andre, K. Döös and P. R. Jonsson, 2012: Identification of subpopulations from connec- tivity matrices. Ecography, 35(11), 1004–1016.

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LIST OF PUBLICATIONS

Kapsch, M. L., M. Kunz, R. Vitolo and T. Economou, 2012: Long term trends of hail related weather types in an ensemble of regional climate models using a Bayesian approach. Journal of Geophysical Re- search, 117, D15107–.

Karl, M., C. Leck, A. Gross and L. Pirjola, 2012: A study of new particle formation in the marine boundary layer over the central Arctic Ocean using a flexible multicomponent aerosol dynamic model. Tellus. Series B, Chemical and physical meteorology, 64, 17158–.

Khosrawi, F., R. Mueller, J. Urban, M. H. Proffitt, G. Stiller, M. Kiefer, S. Lossow, D. Kinnision, F. Ol- schewski, M. Riese and D. Murtagh, 2012: Assessment of the interannual variability and impact of the QBO and upwelling on tracer-tracer distributions of N2O and O3 in the tropical lower stratosphere. At- mospheric Chemistry and Physics Discussions, 12, 22629– 22685.

Kjellsson, J. and K. Döös, 2012a: Lagrangian decomposition of the Hadley and Ferrel cells. Geophysical Research Letters, 39, L15807–.

Kjellsson, J. and K. Döös, 2012b: Surface drifters and model trajectories in the Baltic sea. Boreal Envi- ronment Research, 17(6), 447–459.

Langen, P. L., R. G. Graversen and T. Mauritsen, 2012: Separation of contributions from radiative feedbacks to polar amplification on an aquaplanet. Journal of Climate, 25(8), 3010–3024.

Lewinschal, A., A. M. L. Ekman and H. Körnich, 2012: The role of precipitation in aerosol-induced changes in northern hemisphere wintertime stationary waves. Climate Dynamics, in press.

Liakka, J., 2012: Interactions between topographically and thermally forced stationary waves: implications for ice-sheet evolution. Tellus. Series A, Dynamic meteorology and oceanography, 64, 11088–.

Liakka, J., J. Nilsson and M. Löfverström, 2012: Interactions between stationary waves and ice sheets: linear versus nonlinear atmospheric response. Climate Dynamics, 38(5-6), 1249–1262.

Liu, X., R. C. Easter, S. J. Ghan, R. Zaveri, P. Rasch, X. Shi, J. F. Lamarque, A. Gettelman, H. Morrison, F. Vitt, A. Conley, S. Park, R. Neale, C. Hannay, A. Ekman, P. Hess, N. Mahowald, W. Collins, M. J. Iacono, C. S. Bretherton, M. G. Flanner and D. Mitchell, 2012: Toward a minimal representation of aerosols in climate models: description and evaluation in the Community Atmosphere Model CAM5. Geos- cientific Model Development, 5(3), 709–739.

Mårtensson, S., M. Meier, P. Pemberton and J. Haapala, 2012: Ridged sea ice characteristics in the Arctic from a coupled multicategory sea ice model. Journal of Geophysical Research, 117, C00D15–.

McLinden, C. A., A. E. Bourassa, S. Brohede, M. Cooper, D. A. Degenstein, W. J. F. Evans, R. L. Gat- tinger, C. S. Haley, E. J. Llewellyn, N. D. Lloyd, P. Loewen, R. V. Martin, J. C. McConnell, I. C. McDade, D. Murtagh, L. Rieger, C. von Savigny, P. E. Sheese, C. E. Sioris, B. Solheim and K. Strong, 2012: OSIRIS A decade of scattered light. Bulletin of the American Meteorological Society, 93(12), 1845–1863.

Meier, M., H. C. Andersson, B. Arheimer, T. Blenckner, B. Chubarenko, C. Donnelly, K. Eilola, B. G. Gustafsson, A. Hansson, J. Havenhand, A. Hoglund, I. Kuznetsov, B. R. MacKenzie, B. Müller-Karulis, T. Neumann, S. Niiranen, J. Piwowarczyk, U. Raudsepp, M. Reckermann, T. Ruoho-Airola, O. P. Sav- chuk, F. Schenk, S. Schimanke, G. Vali, J.-M. Weslawski and E. Zorita, 2012: Comparing reconstructed past variations and future projections of the Baltic Sea ecosystem, first results from multi model ensemble simulations. Environmental Research Letters, 7(3), 034005–.

54 BIENNIAL REPORT 2011 – 2012

LIST OF PUBLICATIONS

Mortin, J., T. M. Schrøder, A. W. Hansen, B. Holt and K. C. McDonald, 2012: Mapping of seasonal freeze-thaw transitions across the pan-Arctic land and sea ice domains with satellite radar. Journal of Geophysical Research, 117, C08004–.

Neu, U., M. G. Akperov, N. Bellenbaum, R. Caballero and J. E. A. Hanley, 2012: IMILAST – a community effort to intercompare extratropical cyclone detection and tracking algorithms: assessing method- related uncertainties. Bulletin of the American Meteorological Society. In press.

Nilsson, J. A. U. and P. Lundberg, 2012: A comparatively general solution of the shelf-wave problem. Continental Shelf Research, 34, 26–29.

Partridge, D. G., J. A. Vrugt, P. Tunved, A. Ekman, H. Struthers and A. Sorooshian, 2012: Inverse modeling of cloud-aerosol interactions: Part 2: Sensitivity tests on liquid phase clouds using a Markov chain Monte Carlo based simulation approach. Atmospheric Chemistry and Physics, 12(6), 2823–2847.

Rapp, M., J. M. C. Plane, B. Strelnikov, G. Stober, S. Ernst, J. Hedin, M. Friedrich and U.-P. Hoppe, 2012: In situ observations of meteor smoke particles (MSP) during the Geminids 2010: contraints on MSP size, work function and composition. Annales Geophysicae, 30, 1611–1622.

Revell, L. E., G. E. Bodeker, D. Smale, R. Lehmann, P. E. Huck, B. E. Williamson, E. Rozanov and H. Struthers, 2012: The effectiveness of N2O in depleting stratospheric ozone. Geophysical Research Let- ters, 39, L15806–.

Sedlar, J., M. D. Shupe and M. Tjernström, 2012: On the relationship between thermodynamic structure and cloud top, and its climate significance in the Arctic. Journal of Climate, 25(7), 2374–2393.

Sterl, A., R. Bintanja, L. Brodeau, E. Gleeson, T. Koenigk, T. Schmith, T. Semmler, C. Severijns, K. Wyser and S. Yang, 2012: A look at the ocean in the EC-Earth climate model. Climate Dynamics, 39(11), 2631– 2657.

Sun, L., X. Li, T. Hede, Y. Tu, C. Leck and H. Ågren, 2012: Molecular dynamics simulations of the surface tension and structure of salt solutions and clusters. Journal of Physical Chemistry B, 116(10), 3198– 3204.

Syed, F. S., H. Körnich and M. Tjernström, 2012a: On the fog variability over south Asia. Climate Dy- namics, 39(12), 2993–3005.

Syed, F. S., J. H. Yoo, H. Körnich and F. Kucharski, 2012b: Extratropical influences on the inter-annual variability of South-Asian monsoon. Climate Dynamics, 38(7-8), 1661–1674.

Thompson, B., M. Jakobsson, J. Nilsson, J. Nycander and K. Döös, 2012: A model study of the first ven- tilated regime of the Arctic Ocean during the early Miocene. Polar Research, 31, 10859–.

Tjernström, M., C. E. Birch, I. M. Brooks, M. D. Shupe, P. O. G. Persson, J. Sedlar, T. Mauritsen, C. Leck, J. Paatero, M. Szczodrak and C. R. Wheeler, 2012: Meteorological conditions in the Central Arctic summer during the Arctic Summer Cloud Ocean Study (ASCOS). Atmospheric Chemistry and Physics, 12(15), 6863–6889.

Von Hobe, M., S. Bekki, S. Borrmann, F. Cairo, F. D’Amato, G. Di Donfrancesco, A. Doernbrack, A. Ebersoldt, M. Ebert, C. Emde, I. Engel, M. Ern, W. Frey, S. Grissbach, J.-U. Grooss, T. Gulde, G. Guenther, E. Hoesen, L. Hoffmann, V. Homonnai, C. R. Hoyle, I. Isaksen, D. Jackson, I. Janosi, K. Kandler, C. Kalicinsky, A. Keil, S. M. Khaykin, F. Khosrawi et al, 2012: Reconciliation of essential process parameters for an enhanced predictability of Arctic stratospheric ozone loss and its climate interactions. Atmospheric Chemistry and Physics Discussions, 12, 30661–30754.

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LIST OF PUBLICATIONS

Weigel, K., L. Hoffmann, G. Guenther, F. Khosrawi, F. Olschewski, P. Preusse, R. Spang, F. Stroh and M. Riese, 2012: A stratospheric intrusion at the subtropical jet over the Mediterranean Sea: air-borne remote sensing observations and model results. Atmospheric Chemistry and Physics, 12(18), 8423–8438.

Zábori, J., R. Krejci, A. M. L. Ekman, E. M. Mårtensson, J. Ström, G. de Leeuw and E. D. Nilsson, 2012: Wintertime Arctic Ocean sea water properties and primary marine aerosol concentrations. Atmospheric Chemistry and Physics, 12(21), 10405–10421.

Zveryaev, I. I. and A. A. Hannachi, 2012: Interannual variability of Mediterranean evaporation and its relation to regional climate. Climate Dynamics, 38(3-4), 495–512.

2013

Achtert, P., M. Khaplanov, F. Khosrawi and J. Gumbel, 2013: Pure rotational-Raman channels of the Esrange lidar for temperature and particle extinction measurements in the troposphere and lower stratosphere. Atmospheric Measurement Techniques, 6(1), 91–98.

Bahrami, F., H. Taghvafard, J. Nycander and A. Mohammadi, 2013: Stability investigation for steady solutions of the barotropic vorticity equation in R-2. Communications in Nonlinear Science & Numerical Simulation, 18(3),541–546.

Ballarotta, M., S. Drijfhout, T. Kuhlbrodt and K. Döös, 2013: The residual circulation of the Southern Ocean: Which spatio-temporal scales are needed? Ocean Modelling, 64, 46–55.

Claesson, J. and J. Nycander, 2013: Combined effect of global warming and increased CO2-concentration on vegetation growth in water-limited conditions. Ecological Modelling, 256, 23–30.

Eilola K, S. Mårtensson, and H.E.M. Meier, 2013: Modeling the impact of reduced sea ice cover in future climate on the Baltic Sea biogeochemistry. Geophysical Research Letters Vol. 40, 149-154.

Goldner, A., M. Huber and R. Caballero, 2013: Does Antarctic glaciations cool the world? Climate of the Past, 9(1), 173–189.

Green, J. A. M. and J. Nycander, 2013: A comparison of tidal conversion parameterizations for tidal models. Journal of Physical Oceanography, 43(1), 104–119.

Hede, T., C. Leck, L. Sun, Y. Tu, and H.A. Ågren, 2013: A theoretical study revealing the promotion of light absorbing carbon particles solubilisation by natural surfactants in nanosized water droplets. Atmos- peric Science Letters, 14(2), 86-90.

Hieronymus, M. and J. Nycander, 2013: The buoyancy budget with a nonlinear equation of state. Journal of Physical Oceanography, 43(1), 176–186.

Holtslag, A. A. M., G. Svensson, P. Baas, S. Basu, B. Beare, A. C. M. Beljaars, F. C. Bosveld, J. Cuxart, J. Lindvall, T. Mauritsen, G. J. Steeneveld, M. Tjernström, and B. J. H. Van De Wiel, 2013: Diurnal cycles of temperature and wind – Still a challenge for weather and climate models. Submitted to Bulletin of the American Meteorological Society, in press.

Kapsch, M-L, R.G. Graversen, M. Tjernström: Springtime atmospheric transport and the control of Artic summer sea-ice extent. Nature Climate Change, in press.

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Kirkevåg, A., T. Iversen, O. Seland, C. Hoose, J. E. Kristjansson, H. Struthers, A. M. L. Ekman, S. Ghan, J. Griesfeller, E. D. Nilsson and S. M. Schulz, 2013: Aerosol-climate interactions in the Norwegian Earth System Model NorESM1-M. Geophysical Model Development, 6, 207–244.

Kupiszewski, P., C. Leck, M. Tjernström, S. Sjogren, J. Sedlar, M. Graus, M. Müller, B. Brooks, E. Swietlicki, S. Norris, and A. Hansel, 2013, Vertical profiling of aerosol particles and tracer gases over the central Arctic Ocean during summer, Atmospheric Chemistry and Physics Discussions, 13, 1–63.

Koenigk, T., L. Brodeau, R. G. Graversen, J. Karlsson, G. Svensson, M. Tjernström, U. Willén, and, K. Wyser, 2013: Arctic Climate Change in 21st Century CMIP5 Simulations with EC-Earth. Climate dynamics, in press.

Leck, C., Q. Gao, F. Mashayekhy Rad, and U. Nilsson, 2013, Size resolved airborne particulate polysaccharides in summer high Arctic, 2013, Atmospheric Chemistry and Physics Discussions, 13, 9801–9847, www.atmos-chem-phys-discuss.net/13/9801/2013/ doi:10.5194/acpd-13-9801-2013.

Lindvall, J., G. Svensson and C. Hannay, 2013: Evaluation of near surface parameters in the two versions of the atmospheric model in CESM1 using flux station observations. Journal of Climate, 26(1), 26–44.

Nilsson, J., P. L. Langen, D. Ferreira and J. Marshall, 2013: Ocean-basin geometry and the salinification of the Atlantic Ocean. Journal of Climate, in press.

Reid, W., P. Achtert, N. Ivchenko, P. Magnusson, T. Kuremyr, V. Shepenkov and G. Tibert, 2013: Tech- nical Note: A novel rocket-based in situ collection technique for mesospheric and stratospheric aerosol particles. Atmospheric Measurement Techniques, 6, 777–785.

Sriver, R., H. Matthew and L. Chafik, 2013: Excitation of equatorial Kelvin and Yanai waves by tropical cyclones in an ocean general circulation model. Earth System Dynamics, 4(1), 1–10.

Struthers, H., A. M. L. Ekman, P. Glantz, E. M. Mårtensson, K. Noone and E. D. Nilsson, 2013: Climate- induced changes in sea salt aerosol number emissions: 1870 to 2100. Journal of Geophysical Research, 118, 1–13.

Zhang, Q., H. Körnich and K. Holmgren, 2013: How well do reanalyses represent the southern African precipitation? Climate Dynamics, 40(3-4), 951–962.

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S T A F F

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S T A F F

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S T A F F

STAFF MEMBERS (AS OF DECEMBER 2012)

SCIENTISTS

BENDER, Frida HEDIN, Jonas ROQUET, Fabien BRODEAU, Laurent KARLSSON, Bodil RODHE, Henning CABALLERO, Rodrigo KHOSRAWI, Farahnaz SAVRE, Julien CARON, Louis-Philippe LECK, Caroline SIGRAY, Peter DÖÖS, Kristofer LEJENÄS, Harald STEGMAN, Jacek EKMAN, Annica LINDVALL, Johannes SVENSSON, Erik ENGSTRÖM, Anders LUNDBERG, Peter SVENSSON, Gunilla GRAND GRAVERSEN,Rune MEGNER, Linda TJERNSTRÖM, Michael GUMBEL, Jörg NILSSON, Johan TYAGI, Bhishma HANNACHI, Abdel NYCANDER, Jonas WITT, Georg (emeritus)

RESEARCH STUDENTS

ACHTERT, Peggy HIERONYMUS, Jenny PEMBERTON, Per BALLAROTA, Maxime HIERONYMUS, Magnus RANJHA, Raza CARLSON, Henrik HÖPNER, Friederike SOTIROPOULOU, Georgia CHAFIK, Leon HULTGREN, Kristofer SALIH, Abubakr CLAESSON, Jonas KAPSCH, Marie-Luise WESSLÈN, Cecilia FALAHAT, Saeed KJELLSSON, Joakim WOODS, Cian FRANSNER, Filippa LEWINSCHAL, Anna HAMACHER-Barth, Evelyne LEUNG, WING HANLEY, John LÖFVERSTRÖM, Marcus HEDE, Thomas MORTIN, Jonas

ADMINISTRATIVE AND TECHNICAL STAFF

BERGSTRÖM, Anna-Karin ERICSSON, Susanne SÖDERLUND, Jan BJÖRLING, Birgitta HALLENGREN, Göran TIBERG, Eva BURGER, Mikael IBANESCU, Iulia WALBERG, Nils BÄCKLIN, Leif JOHANSSON, Pat ÖHRSTRÖM, Agneta DE HAAN, Albert KHAPLANOV, Mikhail ÖMAN, Åsa

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V I S I T O R S

62 BIENNIAL REPORT 2011 – 2012

V I S I T O R S

VISITORS

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V I S I T O R S

VISITORS

DYNAMIC METEOROLOGY

Elagib, Nadir – Cologne University of Applied Sciences, Germany

Guillas, Serge – University College London, UK

Holtslag, Bert – Wageningen University, The Netherlands

Huber, Matthew – Purdue University, USA

Iudicone, Daniele – Stazione Zoologica Anton Dohrn, Italy

Kay, Jennifer – National Center for Atmospheric Research (NCAR), Boulder, Colarado, USA

Källén, Erland – ECMWF, UK

Liu, Qinyu – Ocean University of China, China

Liu, Zhengyu – Center For Climate Research, USA

Magnusdottir, Gudrun – University of California, USA

Martins, Joao – University of Lisbon, Portugal

Nappo, Carmen – CJN Research Meteorology, Knoxville, Tennesee, USA

Nisancioglu, Kerim – Bjerknes Centre for Climate Research, Norge

Oliveira, Irene – Universidade de Tras-os-Montes e Alto Douro (UTAD), Portugal

Risi, Camille – CNRS, France

Roe, Gerard – University of Washington, USA

Semedo, Alvaro – Base Naval, Lisbon, Portugal

Shutts, Glenn – Met Office, UK

Sura, Philip – Florida State University, USA

Syed, Faisal Saeed – Pakistan Met Office, Islamabad, Pakistan

Turner, Andrew – Reading University, UK

Zagar, Nedjeljka – University of Ljubljana, Slovenia

Zveryaev, Igor – P.P. Shirshow Institute of Oceanography, Moscow, Ryssland

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PHYSICAL OCEANOGRAPHY

Bahrami, Fariba – University of Tehran, Iran

Cuthbertson, Alan – Hariot-Watt University, Edinburgh, UK

Dijkstra, Henk – Utrecht University, The Netherlands

Drijfhout, Sybren – KNMI, De Bilt, The Netherlands

Fallah, Hanuyeh – IPM, Iran

Groeskamp, Sjoerd – University of Tasmania, Australia

Laanearu, Janek – Tallin Tech. Univ Tallin, Estland

Laliberte, Frederic – University of Toronto, Canada

Madec, Gurvan – University of Southampton, UK

Marchal, Oliver – Woods Hole Oceanographic Institution, USA

McDougall, Trevor – CSIRO Marine and Atmospheric Research, Hobart, Australia

Nilsson, Jenny – National Institute of Geophysics and Volcanology, Italy

Nurser, George – National Oceanography Centre, Southampton, UK

Pierrehumbert, Raymond – University of Chicago, USA

Rossby, Thomas – University of Rhode Island, USA

Skagseth, Öystein – Institute of marine research, Norge

Zika, Jan – University of Southampton, UK

CHEMICAL METEOROLOGY

Brooks, Barbara – University of Leeds, UK

Brooks, Ian – University of Leeds, UK

Budhavant, Krishnakant – Maldives Climate Observatory, Republic of Maldives

Canut, Guylaine – University of Leeds, UK

Charlson, Robert J – University of Washington, Seattle, USA

Coz Diego, Esther – CIEMAT, Spain

Heintzenberg, Jost – Institute for Tropospheric Research, Leipzig, Germany

Held, Andreas – University of Bayreuth, Germany

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V I S I T O R S

Henderson-Sellers, Ann – Macyuarie University, Australia

Huisman, Andrew – University of Wisconsin-Madison, USA

Karl, Matthias – Joint Research Centre, European Commission, Ispra, Italy

Kulshrestha, Umesh – JN University, New Delhi, India

McGuffie, Kendal – University of Technology, Australia

Rauschenberg, Carlton – Bigelow Laboratory for Ocean Sciences, Maine, USA

Rizzo, Luciana – Universidade Federal de Sao Paulo, Brazil

Saltzman, Eric – University of Miami, USA

Wang, Chien - MIT, USA

ATMOSPHERIC PHYSICS

Barjatya, Aroh – Daytona Beach College of Arts & Science, USA Bauerecker, Sigurd – Technische Universität Braunschweig, Germany Benze Susane – University of Colorado, USA Bilén, Sven – Pennsylvania State University, USA Blum, Ulrich – University of Bonn, Germany Bourassa, Adam – University of Saskatchewan, Canada Friedrich, Martin – Technical University Graz, Austria Gabriel, Alexander – Leibniz-Institute of Atmospheric Physics, Germany Hervig, Mark – GATS Incorporation, Driggs, Idaho, USA Hoppe, Ulf – University of Tromso, Norge Kubin, Anne – Freie Universität Berlin, Germany Kucharski, Fred – Abdus Salam International Centre for Theoretical Physics, Trieste, Italy Lehmacher, Gerald – Clemson University, USA Lossow, Stefan – Freie Universität Berlin, Germany Orsolini, Yvan – Bjerknes Centre for Climate Research, Norge Rapp, Markus – DLR, Germany Reimuller, Jason – University of Colorado, USA Robertson, Scott – University of Colorado, USA Shukla, Jagadish – George Mason University, Fairfax, Virgina, USA Slanger, Tom – SRI International, Menlo Park, California, USA

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V I S I T O R S

Sternovsky, Zoltan – University of Colorado, USA Strelnikov, Boris – Leibniz-Institute of Atmospheric Physics, Germany Taylor, Mike – Utah State University, USA Frey, Wiebke – Max-Planck-Institut für Chemie, Germany

ROSSBY VISITING FELLOWS

Gan, Thian – University of Alberta, Canada Heifetz, Eyal – Tel-Aviv University, Israël Zorita, Eduardo – Institute for Coastal Research, Germany

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F I N A N C E S

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F I N A N C E S

FINANCES

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F I N A N C E S

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F I N A N C E S

FINANCES

Approximate funding MSEK

2011 2012

International Meteorological Institute (IMI) Governmental support 2.1 2.2

Department of Meteorology, Stockholm University (MISU) Governmental support 29.4 30.5

IMI/MISU Additional external financial support 23.3 22.9

During the past two years the additional financial support has been obtained from:

European Space Agency

Swedish Environmental Protection Agency

European Commission

Foundation for Strategic Environmental Research (MISTRA)

Swedish National Space Board (Rymdstyrelsen)

The Swedish Research Council (VR)

The Swedish Research Council for Environment Agrcultural Sciences and Spatial Planning (FORMAS)

NORFA

Office of Naval Research (ONR)

STINT

Totalförsvarets Forsknings Institut (FOI)

The Knut and Alice Wallenberg Foundation (KAW)

United Nations Environment Programme (UNEP)

VINNOVA

Swedish Nuclear Fuel and Waste Management Co (SKB)

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PHD THESES

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PHD THESES

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PHD THESES

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PHD THESES

PhD THESES 2009-2012

Frida A-M. Bender, 2009, Earth’s Albedo in a Changing Climate Erik Engström, 2009, Characterization of soot in air and rain over southern Asia Jonas Hedin, 2009, Rocket-borne in situ measurements in the middle atmosphere Johannes Karlsson, 2009, The influence of clouds on Earth’s radiation budget in global climate change Linus Magnusson, 2009, Sampling uncertainties in ensemble weather forecasting Bodil Widell, 2009, Development of GC-HRMS procedures for determination of naturally occuring polar compounds in various environmental applications Jenny Lunden, 2010, Atmospheric DMS in the high Arctic Joseph Sedlar, 2010, Artic clouds – interactions with radiation and thermodynamic structure Moundheur Zarroug, 2010, Asymptotic methods applied to some oceanography-related problems Anders Engström, 2011, Aerosol-cloud interaction from an observational and modelling perspective Faisal Saeed Syed, 2011, On the intra-seasonal to decadal climate variability over South-Asia Johan Liakka, 2011, The mutual interaction between the time-mean atmospheric circulation and continental-scale ice sheets Hanna Corell, 2012, Applications of ocean transport modelling Lisa Bengtsson, 2012, On the convective-scale predictability of the atmosphere Qiuju Gao, 2012, Marine biogenic polysaccharides as a potential source of aerosol in the high Arctic: To- wards a link between marine biology and cloud formation

BIENNIAL REPORT 2011 – 2012 75

A C R O N Y M S

76 BIENNIAL REPORT 2011 – 2012

A C R O N Y M S

ACRONYMS

BIENNIAL REPORT 2011 – 2012 77

A C R O N Y M S

ACRONYMS ABC Atmospheric Brown Clouds ACC Antarctic Circumpolar Current ACE Aerosol Characterisation Experiment ACIA Arctic Climate Impact Assessment ADM Atmospheric Dynamics Mission ALOMAR Arctic Lidar Observatory for Middle Atmosphere Research AO Arctic Oscillation AOE Arctic Ocean Expedition AP Atmospheric Physics (a section of IMI/MISU) APS Aerodynamic Particle Sizer ARCMIP Arctic Regional Climate Model Intercomparison Project ASCOS Arctic Summer Cloud-Surface Study ASTAR Arctic Study of Tropospheric Aerosols, Clouds and Radiation AWI Alfred Wegener Institute CABLE Co-operation Alomar Bi-static Lidar Experiment CACGP Commission on Atmospheric Chemistry and Global Pollution CAD Composition of Asian Deposition CANTAT Canadian Transatlantic Circulation CARMA Commnity aerosol and radiation model för atmospheres CCM Chemistry climate model CCN Cloud Condensation Nuclei CIRES Cooperative Institute for Research in the Environmental Sciences CM Chemical Meteorology (a section of IMI/MISU) CMAM Canadian Middle Atmosphere Model COAMPS Coupled Ocean/Atmospheric Mesoscale Prediction System CPC Condensation Particle Counter CW Coastal Waves DM Dynamic Meteorology (a section of IMI/MISU) DMPS Differential mobility particle sizer DMS Dimethyl Sulfide DMSP Dimethyl Sufonium Propionate DNMI Det Norske Meteorologiske Institutt DOAS Differential Optical Absorption Spectroscopy DSMC Direct Simulation Monte Carlo technique for rarefied flows EAPS Earth, Atmospheric and Planetary Sciences eARI enhanced Alomar Research Infrastructure ECMWF European Centre for Medium Range Weather Forecasts ECOMA Existence and Charge state Of Meteoric dust in the middle Atmosphere EPS Exopolymer Secretions ERA ECMF Re-Analysis ESA European Space Agency EUFAR European Fleet for Airborne Research

78 BIENNIAL REPORT 2011 – 2012

A C R O N Y M S

FSSP Forward scattering spectrometer probe GABLS GEWEX Atmospheric Boundary Layer Study GC Gas Chromatograph GCM General Circulation Model GEWEX Global Energy and Water Cycle Experiment HIRLAM High Resolution Limited Area Model ICSU International Council of Science IGBP International Geosphere-Biosphere Programme IITM Indian Institue of Tropical Meteorology IMI The International Meteorological Institute in Stockholm IN Ice Nuclei INDOEX Indian Ocean Experiment IPCC Intergovernmental Panel on Climate Change IPY International Polar Year ISAC International Study of Arctic Change ITM Institute of Applied Environmental Research LWC Liquid Water Content MAGIC Mesospheric Aerosols Genesis, Interaction and Composition MBL Marine Boundary Layer MISU Meteorologiska Institutionen, Stockholms Universitet (Department of Meteorology, Stockholm University) MIUU Meteorologiska Institutionen, Uppsala Universitet MPI Max-Planck-Institute MSA Methane Sulphonic Acid MSLP Mean-Sea-Level pressure NADW North Atlantic Deep Water NCAR National Center for Atmospheric Research, Boulder, USA NEAQS The New England Air Quality Study NLC NoctiLucent Clouds NOAA National Oceanic and Atmospheric Administration, USA NRL Naval Research Laboratory, Washington D.C. OEM Optimal Estimation Method OPC Optical Particle Counter OSIRIS Odin Spectrometer and InfraRed Imaging System PRMIER Process Exploration Measurements Infrared Emitted Radiation PSAP Particle Soot Absorption Photometer RAPIDC Regional Air Pollution in Developing Countries RCA Rossby Centre Atmospheric model RCO Rossby Center Ocean model SAT Surface Air Temperature SEI Stockholm Environment Institute SHEBA Surface Heat Budget of the Arctic Ocean Sida Swedish International Development Cooperation Authority SLAM Scattered Lyman-Alpha in the Mesophere

BIENNIAL REPORT 2011 – 2012 79

A C R O N Y M S

SMHI Swedish Meteorological and Hydrological Institute SMR Sub-Millimetre Radiometer SNSB Swedish National Space Board SST Sea Surface Temperature STEAM Stratosphere-Troposphere Exchange And climate Monitor SU Stockholm university SWECLIM SWEdish regional CLImate Modelling programme SWIFT Stratospheric Wind Interferometer for Transport studies TA Transnational Access TEM Transmission electron microscopy THC ThermoHaline Circulation TOA Top of Atmosphere TRACE Transport and Chemical Evolution UT/LS Upper Troposphere/Lower Stratosphere WCRP World Climate Research Programme WMO World Meteorological Organization ZAMM Zeitschrift für Angewandte Mathematik und Mechanik

80 BIENNIAL REPORT 2011 – 2012