Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 4 1 Chemistry and Physics Discussions Atmospheric , U. Lohmann 1 ects of these improvements , and J. Feichter ff 1 , S. Kinne ¨ urich, Switzerland 3 , S. Rast 6 7546 7545 , P. Stier , H. Wan 2,7 1,** ¨ om parameter have been reduced. The paper also points , J. Kazil ects turn out to be the water uptake scheme and cloud mi- ff 1,* , J. Quaas ˚ 5 Angstr ects of the new/updated parameterizations are demonstrated by ff , B. Croft 4 , D. O’Donnell 1,6 The combined e Sensitivity experiments are carried out to analyse the e now at: University of Leipzig, Leipzig, Germany This discussion paper is/has beenand under Physics review (ACP). for Please the refer journal to Atmospheric the Chemistry corresponding final paper in ACP if available. Department of Physics and AtmosphericPacific Science, Northwest Dalhousie National University, Halifax, Laboratory, Richland, Canada NOAA WA, Earth USA System Research Laboratory (ESRL), Boulder, Colorado, USA Max Planck Institute for Meteorology, Hamburg,Cooperative Germany Institute for Research in Environmental Sciences (CIRES), University of University of Oxford, Oxford, UK Institute of Atmospheric and Climate Science, ETH Z now at: Finnish Meteorological Institute, Helsinki, Finland servations. Model simulations are evaluated inagainst terms of measurements aerosol number collected concentrations measurement from sites, twenty and fieldsurements. in campaigns Results terms as indicate a of well generalThe optical as improvement aerosol with properties from size respect to against distribution fixed thebetter and the earlier agreement spatial-temporal version. AERONET with variance the mea- simulated observations.optical by depth Biases HAM2 and in are in the the in earlierout model the version remaining in model aerosol deficiencies that need to be addressed in the future. crophysics. The former leads tolower a troposphere, significant and decrease of consequently aerosol smalleraerosol water optical loading contents and depth; in longer the the lifetime latter due results to in weaker higher in-cloud scavenging. comparing the new model results with those from the earlier version, and against ob- the coupling of aerosolscheme, microphysics and to alternative athe wet two-moment model’s scavenging stratiform capability parameterizations. cloud towith microphysics These climate. represent revisions details extend of the aerosol lifecyclein and the its process interaction representationtion. on The the simulated new aerosol parameterizationsoptical properties that depth have and and largest radiative global e impact distribu- on the global mean aerosol This paper introduces andmodel evaluates ECHAM-HAM. the Major second changes version have ofparameterizations been for the brought aerosol into global nucleation the and aerosol-climate water model,ondary uptake, including organic an new explicit aerosols, treatment modified of emission sec- calculations for sea salt and mineral dust, Abstract 5 6 7 * ** Received: 13 February 2012 – Accepted: 6Correspondence March to: 2012 K. – Zhang Published: ([email protected]) 16 MarchPublished 2012 by Copernicus Publications on behalf of the European Geosciences Union. The global aerosol-climate model ECHAM-HAM, version 2: sensitivity to improvements in process representations K. Zhang Atmos. Chem. Phys. Discuss., 12, 7545–7615,www.atmos-chem-phys-discuss.net/12/7545/2012/ 2012 doi:10.5194/acpd-12-7545-2012 © Author(s) 2012. CC Attribution 3.0 License. 1 2 Colorado, Boulder, Colorado, USA 3 4 S. Ferrachat 5 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , , , , , ; , ; ) ), ects ff 2006 2005 1996 ), and ). The 2009 , , , ( ) and the Folini and Jacobson 2005 ; 2007 Croft et al. Koch et al. Stier et al. ; , , Roeckner et al. 2010 2001 Timmreck et al. Stier et al. , , ; ; ). ) and for investiga- Feichter et al. Stier et al. ; Spracklen et al. Stier et al. 2009 ; 2011 2009 ). ( 2006b , Mashayekhi et al. , , 1991 , 2005 2006 , ). The simulated aerosol mass Wilson et al. , http://aerocom.met.no ). The estimated direct forcing of 2011 ). , Fischer-Bruns et al. ) developed at the Max Planck Insti- 2006 ; , Bergman et al. Stier et al. Niemeier et al. 2011 ; Roeckner et al. Makkonen et al. , 2005 ; Schulz et al. 2009 , , 7548 7547 2004 ), and , 2009 Langner and Rodhe , erent approaches ( Kulmala et al. ). The simulated aerosol optical depth (AOD) and Liu et al. ff Kinne et al. 2010 ; ( ; ects of aerosols, particularly through their impacts on ) and positive bias over the open oceans ( ff Stier et al. 2008 ). The first released version, designed with a focus on , 2008 2007 , ). Apart from being coupled with ECHAM5 ( 2011 , Easter et al. Croft et al. , 2012 ; ; , 2011 2006 cient. Numerical models, together with observational data from Zhang et al. , , Lohmann and Hoose 2004 ffi 2008 ), ; , ¨ , om parameter over the ocean is on the large large side compared to ), the model has been compared with other models and with obser- Hoose et al. Bauer et al. ; 2010 2008 ( ), the complete aerosol module HAM, or substantial parts of it, has been , Kazil et al. 2005 ( ; 2005 , Textor et al. 2006a Bourgeois and Bey Vignati et al. Niemeier et al. 2011 Hoose et al. ; , ; ). The Angstr ). The four-band shortwave radiative transfer scheme in the atmospheric model ; , A series of attempts have been made to identify the sources of these errors and In the past years, through further evaluation as well as various applications, several Since first released in 2005, the model has been widely used in process studies The ECHAM5-HAM model ( eruption and geo-engineering2010 studies (e.g., 2003 Pringle et al. Wild tropospheric aerosols, has been extended into the stratosphere and used in volcanic implemented in several other model systems, for example by 2009 2009 the Moderate Resolution Imaging Spectroradiometer (MODIS)issues, satellite together retrieval. These with theand simplifications the lack made of for physically-basedfurther secondary coupling improvement between organic of aerosols aerosols ECHAM-HAM. and (SOA) clouds, motivated the to improve model performance.dated The to refractive reduce index2007 the for negative black bias carbon of has absorption been aerosol up- optical depth ( Aitken mode particle number concentrationover is the underestimated industrial in the regions lower comparedso troposphere to is aircraft the measurements accumulation ( modemeasurements number ( concentration over the ocean, according to ship biases in ECHAM-HAM haveof been the brought simulated to aerosol attention. absorption For revealed negative example, biases the ( evaluation Kloster et al. extinction profiles has a systematic negative bias in high-latitude regions ( (e.g., tions in the climate impact of aerosols (e.g., clouds, remain insu a variety of sources,complex provide interactions between a aerosols powerful andies tool using climate. for Lessons simple advancing bulk learnt our methodsgradually from (e.g., led understanding earlier to stud- of appreciation the The of newer the models importance havesition of thus and microphysics included size in more distribution, aerosol using detailed modelling. di descriptions of aerosol compo- Although it is widelytant believed role that natural in and determiningsome anthropogenic physical the aerosols processes current in play the an stateQuantifications aerosol impor- of and lifecycle the future are climatic not changes e yet of understood with the certainty. Earth’s climate, aerosols is close to the multi-model mean ( 1 Introduction 2001 budget, residence time, andspread ( optical properties are within the ranges of multi-model cesses from the micro- toof the aerosols global scale, on and the inStier atmospheric return, et calculate dynamics. al. the In radiativevations addition e through to participation the in evaluationvations the presented and AeroCom by Models) (Aerosol model ComparisonsEUCAARI inter-comparison between (European project Obser- Integrated ( projectteractions) on model Aerosol inter-comparison ( Cloud Climate and Air Quality in- tute for Meteorology waseral circulation one model of that thetion can of earlier dynamically aerosols examples predict by the of taking composition into a and account global the size atmospheric most distribu- important gen- chemical and physical pro- Liu et al. 5 5 10 25 15 20 10 25 15 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ; Croft , and 2002 , 2008 ects of im- , ff ) and particulate ). The prognostic ects are analyzed 2 ). A newer aerosol ff Tegen et al. . As in the paper by 6 2004 ). The on-line calcula- 2007 http://www.euclipse.eu/ Cheng et al. , ect of a particular modi- , ff ). 2007 ). Terrestial DMS emissions , 2009 , 2006 , see also , Vignati et al. , and describe the simulation design in 2004 ), coupled to the global climate model Cagnazzo et al. ). 2 , ) is implemented in the model which diag- Schulz et al. Lohmann et al. 2005 1995 7550 7549 ), predicts the evolution of an aerosol ensem- ( , Kloster et al. ). Those of sulfur dioxide (SO ). In this way we attempt to provide a clean evalu- 4 2006a Quaas et al. 2005 , , Stier et al. Pham et al. 2003 ects. Although some of the new features have already been , modissimulator.pdf ff ), as well as a new scheme for calculating the hygroscopic ). Stier et al. ; 2011 ). A more detailed and explicit treatment of SOA was implemented euclipse , ), we concentrate our analysis on aerosols in the troposphere. There 2009 ( 2001 2010 , 2005 , , and this work). A two-moment cloud microphysics scheme is implemented ( Roeckner et al. in the comparison of HAM2 simulations with those from the previous version, 5 . Conclusions drawn from this work are presented in Sect. 2009 3 , cial” HAM2 as reference, and with a single aspect of the model updates reverted to The emissions of sea salt and dust are computed interactively ( The main objective of the present paper is to analyse and quantify the e ffi O’Donnell et al. Kazil et al. sulfate, black carbon and primaryspecifications organic of aerosols AeroCom. (POA) Natural arerine emissions prescribed of following biosphere the dimethyl are sulfide calculated (DMS) online from ( the ma- are prescribed according to variables are the particleconcentration of number each concentration compound present of in each that mode, mode. asGuelle well et as al. the mass prescribed variance in the M7 aerosol module ( ble with five internally(BC), and particulate externally organic matter mixed (POM),distribution compositions: sea sulfate salt of (SS), (SU), this and black mineral aerosol carbon dust population (DU). The is size described by seven log-normal modes with ECHAM5 ( The aerosol module HAM ( Stier et al. are some addtional model updates relatedbeen to included stratospheric in aerosols which the haveNiemeier code not et used yet al. in this study. These developments were presented in 2 Model overview Sect. ation of the impact ofin each Sect. individual modification. Theas combined well e as against observation. Beforethe showing basic these features results, of we provide the a HAM summary model of in Sect. the HAM1 configuration (see Sect. “o downloads/D1.2 point where a secondnew version version, of referred this to aerosol-climate asof model the ECHAM-HAM2 is AeroCom (or model ready simply inter-comparison for HAM2), ( release. participated This in phase II the present paper is a series of sensitivity simulations that are all performed with the noses cloud quantities consistently withinstrument, passive satellite and retrievals samples as frompolar-orbiting the the satellites. spatial MODIS This facilitates and theobservations comparison temporal from between incidences model spaceborne results of instruments. and the the These overpasses revisions of have brought us to the distribtion, and radiative e discussed in the publications citedspecific above, schemes the for authors individual thereinaspects processes. mainly most The concentrated model closely on evaluationabove-cited related was studies to with often ECHAM-HAM limited the were to versions based process that on included in intermediate incremental (unreleased) question. changes code cesses in Furthermore, model and configuration. some As their the of interactionsnonlinear, aerosol the with it pro- is each not other alwaysfication and easy by with to inter-comparing draw results model conclusions reported meteorology on in are the these often e publications. An important part of ( provements in the process representation on the simulated aerosol properties, global growth of aerosol particles. The wet scavengingand schemes coupled have been with updated aerosoltion ( of microphysics dust ( andthis sea salt work). emissions A have satellite also simulator been ( modified ( nucleation parameterization has been( adopted, and additional mechanisms included et al. has been extended with two additional bands ( 5 5 25 20 15 10 15 10 25 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , . ) 4 ), ni- 2 2005 ( O ). Prog- 2 Dentener 1996 ( Horowitz et al. Stier et al. ) simulates the for- 2004 ( ). This allows for detailed erences compared to the ff Feichter et al. ). Emissions of anthropogenic erent modes. Sink processes, 2005 and gas- and aqueous-phase ff , . 2 2 ), and “HAM2” for the new version Vignati et al. 2005 ( Uppala et al. 7552 7551 erent diagnostics. ), are prescribed using three-dimensional monthly ff 3 Stier et al. . In each simulation, one component of the parameter- 4 provides an overview of the updates in HAM2 with respect to ort in general, we will use the term “ECHAM-HAM” (or simply presents the modal structure of the aerosol population in our 1 ff 1 ), and ozone (O 2 http://www-pcmdi.llnl.gov/projects/amip/ ). Each integration starts from a meteorological state that is routinely used in 2006 ). Sulfuric acid gas produced from gas-phase chemistry can either condense on , To evaluate the aerosol properties in HAM2 and their di Since the purpose of this study is to evaluate the aerosol module HAM rather than the Further details of the features mentioned above are described in The aerosol microphysics sub-module M7 of Radiative properties of aerosols are dynamically computed based on their chemical The sulfur chemistry module is based on the work by alternative that is implementedsimulations in carried the out in new this version study but is not given yet in Table set as default. A list of simulation that is required toto draw formulation/configuration sound changes conclusions. in The the responsestude, following and of sections are model are consistently results significant seen in in di magni- earlier version HAM1,model integrations configurations. In are addition,and performed a are using number discussed of the inized sensitivity sub-grid Sect. corresponding simulations processes in are default HAM2 carried is out reverted to the old HAM1 setup, or replaced by an comparison between model results and observations, and also reduces the length of the analysis presented later in the paper. host model ECHAM5, wecal carry fields out towards nudged the ERA-40 simulations, reanalysis which ( relax the meteorologi- We performed simulations ofice the prescriptions year of 2000parison the Project forced ( same by year seaaerosols from surface and the their temperature/sea precusors, Secondprescibed as according Atmospheric well to Model as AeroComet Phase Intercom- biomass al. I burning emission and dataclimate volcanic for simulations aerosols the with are year ECHAM5. 2000nostic The precursors ( initial are concentrations zero. of Three2000 all months of aerosols in integration and each are prog- simulation. performed This prior is to January considered as the spin-up phase and not included in model. 3 Simulation setup the diagram in Fig. and the references therein.exist These so remain far. unchanged In the throughmodel following all parts development model of e versions this that paper,“HAM”). when When mentioning it these is features, necessary ormodel to our distinguish, configuration “HAM1” described will be by used to refer to the specific tions of themeteorological aerosol conditions. size distribution, composition, and mixingcomposition state, (including the as water content) wellup and as particle table established size the using using a the pre-calculated Mie look- theory. existing aerosol particlesaqueous or phase chemistry nucleate is to distributedcoarse to form mode pre-existing soluble aerosol new accumulation particles. mode particles. and Sulfate produced from mation and growth of aerosolacid gas, particles the due coagulation to of particles,to nucleation re-distribution and and of aerosol condensation particle water of uptake. number Thesenamely sulfuric and processes dry mass lead among deposition, di sedimentation and wet deposition, are parameterized as func- nostic variables includesulfate. concentrations Oxidant of fields, DMS, includingtrogen hydroxyl SO dioxide radical (NO (OH), hydrogenmean peroxide model (H output for present-day condition2003 from the MOZART model ( presented here. Table HAM1. Further details and theTo facilitate impacts discussions on in the aerosol following simulation sections are and for discussed the in convenience of Sect. the readers, 5 5 25 20 15 10 15 20 10 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 4 a– 2 SO Kazil 2 ), and ), while H2SO4 in and an or- Kazil et al. 2007 Kazil et al. 4 , ected by the 2004 ) parameteri- ff concentration , O. This param- SO 4 2 2 2007 SO ( 2 and H NUL, uses the HAM1 4 . The right column shows Riipinen et al. 2 SO ; Vignati et al. 2 ), although these processes erent operator-splitting algo- ). The former was the default ff 2006 2008 , 1998 gas equation, on the other hand, , ( ) implemented the scheme of 4 ) parameterization, three-step explicit Kazil and Lovejoy gas in Fig. SO 4 2 2010 ( 2002 SO ( 2 ) to the ) showed with a box model that this scheme 7554 7553 ) gas to aerosol particles is one of the major ) proposed a di Kuang et al. , and removed by nucleation as well as conden- Kulmala et al. 4 ; 2 Kulmala et al. . 2002 SO 2009 ff ( ( 2 2009 equation (cf. Eq. (2) in ¨ aki et al. ( 2004 Kazil et al. ects 4 , ff ). 3 SO 2 ¨ O in the earlier model version was desribed with the scheme aki et al. Vehkam ) or that of 2 /H gas and the balance between its source and sink terms. 4 2002 Kokkola et al. 4 ( Laakso et al. Kokkola et al. SO ) for neutral and charged nucleation of H Vehkam 2 SO 2 2007 ( ¨ aki et al. equation was numerically solved in three consecutive steps, each taking care ). The left column, corresponding to experiment HAM2 d–e). Changing the handling of the H 2 4 ) introduced the assumption that in the cloudy portion of a grid box, all H ) (HAM2 default) nucleation parameterization but the old time stepping method 2 SO Vehkam Switching from To demonstrate the impact of these changes at the global scale, we present vertical Nucleation of H Another major change between HAM1 and HAM2 is the treatment of sulfuric acid 2 2010 2010 (Fig. zation leads to an upwardb), shift due of to the highest aate concentrations strong increase of reduction fine at of particles 150–50 nucleation hParemaining (Fig. at (not in altitudes shown). the of Accordingly, air there 400–150 hPa in is and the more a upper sulfuric moder- troposphere, acid and gas less near the tropical tropopause converging towards the exact solutionnucleation of is the weak. production-condensationoutperformed equation the when original algorithm. In addition to the revised numerics, numerics, and noparts. distinction All between other aspects condensation are in identical in clouds the and three simulations. in the cloud-free rithm in which thestep production-condensation to equation provide is anby solved intermediate a analytically second estimate in step of the accounting sulfuric first for acid nucleation. This gas new concentration, algorithm followed has the advantage of results from the standard HAM2 configuration; The middle column uses the of one process andfor using the explicit time next integration step. to update the H cross-sections of thetogether number with concentration the of mass concentration ultra-fine of (nucleation H mode) particles H ( gas condenses on the largestuble soluble particles particles otherwise. if There there isno is complete aerosol any, removal and nucleation of on takes sulfuric place the within acid largest them. gas insol- in clouds, and ( and without completeTable in-cloud removal (referred toset-up which as includes the experiment HAM2 The conversion of sulfuricmechanisms acid of (H particle formationgas in is produced the by atmosphere. the oxidation Insation of onto the SO already HAM existing model aerosolis sulfuric particles. not acid only The determined strengthabundance by of of the nucleation H nucleation in mechanism, the but model also strongly a of In this section we describeimpact the on model the updates simulated with aerosol respect distributions to and HAM1, properties. and4.1 discuss their Sulfuric acid gas and aerosol nucleation 4 Model updates and their e eterization is based oncalculate laboratory aerosol measurements formation using rates. a Itthe semi-analytical is planetary approach boundary now to layer, the HAM2 default alsoganic nucleation considers compound the scheme via nucleation in cluster of HAM2. activation H In ( choice because it is basedbinary on homogeneous a nucleation thermodynamically theory, consistent andnamical version is conditions of valid (cf. the for Table classical aand Lovejoy broader range of thermody- kinetic nucleation ( of view of thenucleation gas-phase is H a nonlinear process. In the default HAM1 configuration the gas-phase are intentionally limited tonucleation forested pathways areas. are switched In o the standard model configuration,gas. these In the model, production and condensation are linear processes from the point 5 5 25 15 10 20 10 15 20 25 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 3 from iso- 1 − the chemical only ). The SOA therein monoterpenes) pro- ). erent volatility. Anthro- 1 ff − 2005 erent SOA schemes. The , 2011 ff ( ) in which the “M7 original” ). 15 % of the prescribed natural concentration in comparison to concentration seen by the con- 2009 ). These results are discussed in 4 ( 2 4 2006 SO 2 SO , 2 Kanakidou et al. ; O’Donnell et al. gas in HAM2 (not shown). 7555 7556 ) is used for biogenic SOA formation, meaning 4 ). The five SOA products (four from biogenic 2005 Kokkola et al. isoprene and 86.3 Tg yr , kinetic in Table f (not shown). An additional simulation reveals that SO ). The SOA yield, however, is only 3 % and much 2 1 2 1996 ( − 2007 Dentener et al. ( ). Refractive indices of SOA are assumed the same as 2006 1 , semi-volatile condensable species (106.5 Tg yr Stier et al. 1 ) implemented an explicit SOA module in ECHAM-HAM, which − Ng et al. Odum et al. oxidation products, which are assumed non-volatile and convert from monoterpenes). These oxidation products form 15.7 Tg SOA 2011 in the context of comparison with observations. 1 ( 1 − cluster and HAM2 − ect is a clear increase of the H ff 5.3 Dentener et al. , 1 and − H2SO4, in which the first two steps (production and condensation) in the old 5.2 erences between panels e and f in the tropical upper troposphere and above the d–e. In particular, in the near-surface layers, the magnitudes and characteristic ff 2 The spatial distribution of aerosol concentrations also changes substantially. In Fig. When the new SOA scheme is switched on, the interactively computed biogenic O’Donnell et al. Sensitivity experiments have also been performed regarding nucleation in the bound- was assumed to have identical properties to primary organic aerosols (POA). particulate organic matter, POM) simulated by HAM2 with di Sects. 4.2 Secondary organic aerosol (SOA) The first version offollowing HAM the AeroCom had approach a ( veryterpene simple emission treatment was ofexisting oxidized secondary aerosol in organic particles the aerosols ( surface layer and condensed immediately on prene, 12.6 Tg yr per year, which,(19.1 in Tg yr terms ofsmaller absolute than specified value, byemissions, is which AeroCom not were (15 %). not farresult included This away in in reflects from the 5.5 the Tg old the yr totally dominance scheme. to old of The SOA. anthropogenic isoprene scheme emissions we present zonal mean mass concentration of total organic aerosols (also referred to as coarse soluble modes (cf. Fig. those of POA. Further details are given by precursor emissions (441.6duce Tg yr about 119.1 Tg yr two-product model of sources, one from anthropogenicby sources) each are assumed other, to thuscontain be the POA, absorbed modes namely by in POA the which and Aitken SOA insoluble, can Aitken occur soluble, accumulation are soluble, the and same as those that handles aerosols originating frompogenic biogenic (xylene, (isoprene toluene and and monoterpenes) benzene)are sources. and computed The anthro- interactively, while emissions those of of biogenic theTransport precursors and anthropogenic oxidation precursors processes are of prescribed. the precursors,volatile as oxidation well as products the into partitioning gas of semi- and aerosol phases, are explicitly described. The that each biogenic precursorpogenic has oxidation two products oxidation can products bevia of lumped namelist). together di SOA (by formed changingfollowing from model the anthropogenic configuration work sources are of assumed as non-volatile pattern become very similar to Fig. scheme systematically underestimates the sulfuricscenarios acid investigated gas therein. concentrations We in haveHAM2 all carried three out a sensitivity experiment similar to scheme. The e Fig. ary layer (HAM2 time integration scheme are solved together using a simple Euler forward (explicit) the di Southern Hemisphere stormand track in-cloud are condensation caused of the by H the distinction between cloud-free computed condensation rate is thusmodel significantly results overestimated. presented This in explains the Fig. box 1 of itative change in theresults, vertical distribution it of is thedensation worth sulfuric calculation acid noting is gas. the that Toproduction. value understand in Because updated these of HAM1 after the taking large the intoconcentration time H step account has used a in the large climate positive model, bias this intermediate when production is strong. The subsequently results in higher concentrations for the nucleation mode particle number, and a qual- 5 5 25 25 20 15 20 10 10 15 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , for κ ) and value κ erences ff Smith and Smith and 2007 ( Zdanovskii ) and ) and 2 µm), the Smith- r < 1986 1986 ( ( ) formula for the radius ) noticed that the partition- 1986 ( ), now used for all hygroscopic 2010 ( N are connected to the biogenic ◦ 2007 Petters and Kreidenweis , Monahan et al. Monahan et al. ), as one would expect. The di S and 15 ◦ , the new implementation produces stronger Zhang et al. 2011 4 7558 7557 Monahan et al. , 4 µm), and a smoothly merged function for the ). r > 2005 ), which regards an aerosol particle as a solution of ). The absolute and relative contributions of aerosol c mainly reflect the changes in precursor emissions. , a), in contrast, resembles closely the POA distribution 3 N are primarily related to the anthropogenic sources. 3 ◦ 1966 2006 , , ). For an internally-mixed aerosol particle, the overall Petters and Kreidenweis O’Donnell et al. ective soluble mass and used in the calculation of the equilib- 4 Stier et al. ) implemented a semi-empirical water uptake scheme based ff erences to the emission scheme. ff 2011 ciency. erent from two other models using the same microphysics package, ( ff ffi ect of the new scheme is the higher loading in the upper troposphere, ); For mixed particles that contain sulfate but no sea salt, sulfate mass Textor et al. ), but directly apply the ). In HAM1, look-up tables of emission flux against 10-m wind were es- ff ¨ ohler theory ( 1991 1998 1998 ( ( , -K κ Stokes and Robinson ; In HAM2 we still use the source functions of When introducing the new SOA scheme mentioned in the previous subsection, The new scheme results in a significant decrease in water uptake in the lower tropo- Zeleznik range of 2–4 µm withoutof merging, the and source replace functions. As the shown look-up in tables Fig. by online integration ber flux. The ratio ofnow the 7.7 accumulation in mode contrast number to flux 1.6 to that in of HAM1, the and coarse is mode closer is to the value 6.7 that can be derived emissions in the accumulation mode and weaker in the coarse mode in terms of num- is calculated bycompound. taking Having the computed volume-weighted the sum hygroscopicity parameter of of the a parameter particle, of and with each its soluble aerosols in HAM2. Thiseach substance approach (Table uses a prescribed hygroscopicity parameter ing of sea saltwas emission evidently between di accumulation andand attributed coarse the modes di in ECHAM-HAM1 Harrison aerosol over the oceans intions the of model. 10-m The emission wind fluxesHarrison speed are following parameterized the as work func- tablished of using the Monahan formula for smallHarrison particles formula (dry for radius large particlessize range ( in between ( mixed electrolytes. O’Donnell et al. on the to 51 Tg (HAM2),Project the (35 latter Tg, being closerwater to to aerosol the optical depth multi-model (AOD)and average decrease 69.8 from % of 0.105 (HAM2), the and respectively. 74.8 AeroCom % (HAM1) to 0.094 4.4 Sea salt emission Sea salt emission is a primary source of soluble accumulation mode and coarse mode ticle radius can betherefore determined the using aerosol Eq. water (11)computational content. of e In the model, a look-up table issphere used and to a enhance slight increase aloft, reducing the total aerosol water from 75 Tg (HAM1) 1948 dry diameter, the air temperature and relative humidity known, the growth factor of par- assumed, with the water uptake calculated according to the ZSR method ( salt, and some organicwas considered aerosols, only are for non-organic hygroscopic.was particles. In calculated For HAM1, pure using sulfate however,( regression particles, water water fits uptake uptake towas solutions regarded of as the the e rium generalized particle Kelvin density; equation for particles containing sea salt, complete ion dissociation was in the lower troposphere inThe increased Fig. concentrations between 20 sources, while those at 15–40 4.3 Water uptake Water uptake is anaerosol important particles. process In that the real changes world the non-organic size aerosols and that contain optical sulfate properties and/or sea of associated with enhanced SOAcondensable oxidation formation products, due especially high-volatility to productsprene tropical associated oxidation, with convective which iso- condense transport only ofthe at original the very SOA low scheme temperatures. (Fig. Resultsof obtained HAM1 with (see Fig. 5 of most evident e 5 5 25 25 15 20 10 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (1) (2) in mixed- i Tegen et al. Cheng et al. ) contained in the N F ) from satellite retrievals, ). In addition, impact of soil 2005 ( 2006 ( ). The scaled scavenging parameters 1 −  ) 2005 ( Prigent et al. 7560 7559 Laurent et al. . a). The simulated near surface dust concentra- 5 5 269.51 ) made attempts to improve dust emission by mod- 3.42 DU performed using the old soil property data. The − was prescribed for each aerosol mode and cloud type T ). In reality, the partitioning of aerosols between those Stier et al. ) analyzed measurements obtained at the high alpine 2008 − R ( c) in the vicinity of the source regions as well as in the ) emission dataset recommended for AeroCom. In terms 5 2005 is the scavenging parameter for aerosol mode exp( 2007 , ( i , in Kelvin) and the fraction of aerosols ( ect of this update, the standard HAM2 results are compared 2006 + ( ff 0, T 1 , R i  0, R Cheng et al. ) defined as the fraction of the aerosol mass or number concentration ) 0.93 0 T Stier et al. T ( R + ( N N F 273.15 K; F b) and AOD (Fig. = 5 = Dentener et al. 0.031 0 Verheggen et al. ) T decrease with temperature, and are generally smaller than the original values. T = ) which was based on observations from Africa but resulted in considerable bi- ). ( i i ) T ( In HAM1 a constant in-cloud For in-cloud scavenging, the removal rates in our model are a function of a scaveng- To demonstrate the e mix, mix, N 2002 2008 R Consequently wet deposition becomes weaker and aerosol loading larger, especially Using this formula, we have addedof in mixed-phase HAM2 stratiform a clouds: new option for the scavenging parameter R where phase clouds as prescribed by research station Jungfraujoch (Switzerland), andtween derived air the temperature following ( relationship be- cloud droplets or ice crystals: F that is considered topart be of the contained grid in box. the cloud-droplets or(see ice-crystals Table 3 in in thecontained cloudy in cloud-dropletseteors or depends ice-crystals on as detailsand opposed of environmental conditions the to (e.g., temperature particle outside andclouds, characteristics updraft of velocity). (e.g., For these mixed-phase chemical hydrom- composition) The removal of aerosol speciesprocesses from that the atmosphere occur by both precipitation in happens and through below clouds. ing parameter Dust emissions in HAM1 were calculated interactively using the scheme of 4.6 Aerosol wet deposition 4.5 Dust emission and observation (not shown). tion (Fig. downstream areas also increase, which leads to better agreements between model ( ases in East Asia. the modification of East( Asia soil properties is adopted from the workwith of a sensitivity simulation HAM2 of mass flux, therethat the is emitted coarse an mode increasethese particles changes are of are larger emission than presented in in in HAM1. Sect. both Further discussions modes of (not shown), implying ity of dust mobilization.larger Because than those the used satellite-derivedfrictional in roughness the velocity lengths original and were model, fine-tunedRecent a much model in scaling evaluation order factor has had toof revealed to that give AOD be this over a applied North modification reasonable toculation leads Africa, global the does to while not total an the lead emission. overestimate inclusion to significant of improvement soil (not moisture shown). Therefore in in frictional HAM2 velocity only cal- ifying the surface conditions used inaerodynamic the roughness model. length They derived employed by aand new the global East-Asian dataset soil of propertiesmoisture from was taken into account when computing the threshold frictional wind veloc- characteristic spatial pattern ofincreases dust by a emission factor is of largely about 4 unchanged, (Fig. but the strength from the 5 5 20 15 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ). 1997 ( Lohmann Croft et al. S poleward ◦ was used for ). The coupling 1 erences from a ). Heterogenous − ff N/45 kg ◦ 2 1996 ( 2003 ects on model meteo- ( c. Khairoutdinov and Ko- ff Lin and Leaitch 6 cient of 0.005 m ffi ). The new scheme includes prognostic ect shown in Fig. erent vertical levels. Various other factors, ff ff ¨ archer and Lohmann K 2009 7562 7561 Lohmann and Roeckner ( cients were prescribed in HAM1 for rain. For ffi ects of aerosols on stratiform cloud microphysics, ff ) predicted mass concentrations of water vapor, cloud ect the aerosol population via wet scavenging, aerosols b, corresponding to a 8 % decrease in global mean), es- ff 6 ). This simple treatment has been updated by 1996 . AOD reductions occur close to East Asian source regions C when supercooled solution droplets freeze. The production , 6 ◦ 2005 ) introduced a two-moment scheme, with further improvements 38 , − ect of modified in-cloud and below-cloud scavenging is shown by ff Lohmann and Hoose a). The weakening of in-cloud scavenging is potentially beneficial for erent from the work of ). 2007 ff ( 15 C. Internally mixed dust and black carbon aerosols are assumed to act ◦ ect clouds via the direct and semi-direct aerosol e 2009 ff Stier et al. a–b we present the annual mean shortwave cloud radiative forcing sim- , ). Homogeneous ice nucleation in cirrus clouds is assumed to happen at air 7 a). The relative changes are larger in the regions from 45 ) to take into account aerosol and collector size distributions in the rain case, 6 C and 0 2000 ◦ ( In order to explicitly simulate the e In Fig. To the model users we point out that the updates described in this subsection are Below-cloud scavenging by rain and snow are considered separately in HAM. Mode- The combined e 38 Lohmann and Roeckner 2009 parameterized phase changeaccretion) and are precipitation di processes (e.g. autoconversion and equations for number concentrationsas of the cloud default droplets stratiform and cloud ice microphysics crystals, scheme and for is HAM2. used Many details of the gan between aerosols and cloud microphysics isin implemented warm as follows: clouds aerosol is activation Autoconversion described of by cloud the droplets semi-empirical to scheme rain of is parameterized as in While clouds could directlycould a only a rology. Lohmann et al. proposed by and temperatures below rate of ice crystals is computed following (autoconversion, accretion, aggregation), evaporation ofwell rain as and sedimentation meltingdroplet of of number snow, cloud concentrations as (CDNC) ice.surface were Regarding type prescribed stratiform (land as or functions cloud ocean).often of formation, The referred pressure to conversion the and as of aerosol cloud aerosol activation particles or cloud into droplet cloud nucleation droplets – was – not considered. ulated with the standard ECHAM-HAM2 model, as well as the di water and cloud ice by taking into account phase transitions, precipitation processes nucleation happens in the model when− dust exists and the airas temperature lies immersion between nuclei whileContact only freezing externally by mixed blackand carbon dust Hoose is particles not act considered as as contact it nuclei. is quite uncertain ( In the( earlier model ECHAM-HAM1 the stratiform cloud microphysics scheme cloud and below-cloud removal happen atincluding di aerosol source, horizontal andalso relevant vertical in transport determining timescale the and combined pathway, e are available in HAM2 but notimpacts switched on on model as climatology default. is A planned comprehensive for evaluation future of code4.7 their release. Cloud microphysics and its coupling with aerosols and Southern Hemisphere stormthe track high regions, latitudes. However, while this AOD is not increases a are simple primarily addition of at panels a and b, because in- (Fig. since the total aerosoltropics loading (cf. is Fig. considerably smaller in the high latitudes than in the with high aerosol concentrations. the bottom panel of Fig. in middle and high latitude regions, as can been seen from the annualreducing model mean error since AOD HAM1 underestimatedlatitude aerosol regions. mass concentrations in high dependent impaction scavenging coe the impaction scavenging byall snow, modes a ( fixed coe ( and aerosol size ingeographical case locations (Fig. of snow.pecially These over the changes storm yield tracks, and a in reduction mid-latitude continental of areas AOD that at are associated most 5 5 15 10 20 25 25 20 15 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , 5 erent ff ciently ffi er only in ff ¨ ohler theory ect is largely ff CLD and HAM2 . 5 ). The K 49 %) in POM burden, + 1997 ( ) has been implementd into ect on aerosol activation is ff 2000 ( CLD are compared, which di ected by the general model tuning (see, ff Lin and Leaitch erences can still be clearly seen between 2 %). It follows that the autoconversion rate ff < ) without prognostic CDNC. One can see a 7564 7563 , first block), which is in agreement with earlier , an overall increase in aerosol burden can be 5 , respectively. In contrast, the increase in global 5 2 − 1996 ). Further discussion in this aspect can be found in , . Results from the AeroCom intercomparison project 5 CLD that uses the old stratiform cloud microphysics 2010 , Abdul-Razzak and Ghan we mentioned that the modified emission scheme produces and 85 g m 2 . HAM2 also shows a marked increase ( c). Over the North Atlantic and North Pacific, this e ) are also included in the table, so as to place our results in − 4.4 7 4.1 2006 fluxes in the accumulation mode and weaker in the coarse mode, as ). This is mainly related to cloud microphysics and wet deposition. In 5 , we present the annual and zonal mean mass concentration of the five 8 Lohmann and Roeckner number . the two simulations HAM2 and HAM2 6 5.1 Lohmann and Ferrachat erences are, in most cases, considerably smaller than the discrepencies among the To the first order, HAM1 and HAM2 have very similar mass budgets. The relative The four aerosol species other than sea salt have longer lifetimes in HAM2 compared In Fig. As a side remark we point out that the particle size e Another point worth noting is the shorter lifetime of sea salt in HAM2 (Table ff Dentener et al. We start the intercomparisonaerosol with types the shown in annual( Table mean global mass budget of di aerosol types. Consistent with Table 5.1 Global mean aerosol mass budgets and concentrations perspective. di AeroCom models. On thethe two other HAM hand, versions. For di considerably instance in the the nucleation new source version of (Table sulfate aerosol increases coarse mode particles constitutea more determining than role 95 % in the of changes the in total sea sea salt saltto sinks mass, HAM1 we they (Table see play in Table cloud microphysics in terms of modelincrease configuration. of The lifetime, new especially cloud for schemeto the leads weaker soluble to in-cloud an species scavenging. (sulfate, sea salt and SOA), due Sect. highly simplified in the parameterization by fourth block). In Sect. stronger well as an increasethe coarse of mode mass particles become fluxremoved much in larger from than both the in modes HAM1, atmosphere and compared are through to more dry e HAM1. deposition Consequently, and sedimentation. Because simulations are 50 g m mean precipitation rate is onlyin marginal the ( new cloudthe scheme in-cloud is scavenging considerably of aerosols. smaller,version Note which rate, that has as the direct parameters in consequences controllinge.g., all the for climate autocon- models, are a discussions in Sect. which is not surprising considering the inclusion of the explicit SOA module. Table counteracted by larger dropleteas sizes the resulting updated from model theshown). predicts fact In smaller that CDNC terms in than of these prescribed global (cleaner) by mean, ar- the the old liquid model water (not path of the HAM2 5 Evaluation of HAM2 against HAM1Having and documented observations in the previoustheir section individual the new impacts features on infects. simulation model This formulation results, section and compares we thesion now overall HAM1, move behavior and on of when to HAM2 possible, against their with observations. that combined of ef- the earlier ver- clear reduction in cloudthe forcing Southern in Hemisphere the storm track, marineliquid water caused stratocumulus path predominantly (Fig. regions, by and changes increase in the in cloud based activation scheme by HAM2, and is evaluated in Stier et al. (2012). scheme ( sensitivity experiment HAM2 5 5 25 15 15 20 10 10 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | . ) ff a– E– 11 and ◦ STP 10 9 2010 i). This , 3 − 10 4000 cm Kazil et al. ). Inclusion of the > ; ), and the British At- 2008 2007 ( , g–i) the maxima at 120 h) is better represented. The 10 source regions (Fig. , results from the vertical trans- ). The geographical coverage is 10 2 4.2 Kuang et al. sources in Asia and the USA. The air Riipinen et al. ). Further details of the measurement 2 ; 9 . The results are very similar to Fig. 3 in on the T63 Gaussian grid) to produce the A1 ◦ http://data.eol.ucar.edu/ . As for model simulations, we first vertically 2006 7566 7565 , 10 ), the National Center for Atmospheric Research in the Appendix. For the evaluation here, each mea- http://badc.nerc.ac.uk erent locations. In the low latitude regions (Fig. A1 ff Kulmala et al. W are caused by strong SO b, e) are closer to the observation. The east-west gradient in the ◦ ), thus are not discussed futher in this paper. 10 STP) in the surface layers over the SO reveals that both model versions can correctly capture the main fea- ) and longitude interval (1.875 3 2005 ( − 10 10 , last row). Note that the observations suggest very high CN concentrations 10 and 100–60 ◦ j–l). 4000 cm Figure Comparing the two HAM versions, we see that the new model produces in general > cluster activation scheme ( overestimation of CN(Fig. concentrations in the( clean regions isfeature also is missing reduced in the in standardin HAM2 HAM1 and HAM2 HAM2 with simulations, but the can be kinetic reproduced nucleation scheme of dry diameter (0.01 µm). distribution. calculated by integrating the simulated number size distribution above the lower cut-o can also improve the results, but not as satisfactorily.5.3 The results are shown Aerosol in size Fig. distribution in theIn boundary observational layer studies itconcentrations is into log-normal a probability common densityacteristics practice functions by to and a summarize fit their few theour char- parameters. model measured evaluation Such since aerosol records HAM number uses are the relatively same modal straightforward method to to describe use aerosol in size tures of CN distribution at di surface. In the Northern180 Hemisphere midlatitudes (Fig. over Canada, Greenland and the10 Northern Polar Region is much cleaner (Figs. better results. For examplein the HAM2 high concentrations (Fig. inupper the troposphere upper over tropical the troposphere Northwest Pacific (Fig. ple average for each longitude and latitude band. The CN concentration in the model is f) the(1013.25 hPa, concentrations 273.15 K)] are due to highest strong nucleation, in and decrease the quickly towards upper the troposphere [ Indian Ocean, and near the North Pole (Fig. interpolate the daily outputthe to same height location levels, and pick in out the the same CN month concentration as occuring a at measurement, then compute the sam- of aircraft measurements betweenley the Research years Center 1991 of and Nationalhttp://www-air.larc.nasa.gov/data.htm 2008 Aeronautics obtained and from Space Administration theEarth (NASA Lang- Observing LaRC, Laboratory (NCAR EOL, mospheric Data Centre (BADC, mainly the Pacific Ocean, with a few additional flights over the North Atlantic and the panels in the rightmost column of Fig. Stier et al. clei (CN, i.e. aerosol particles of dry diameter larger than 0.01 µm) using a collection campaigns are given in Table sured concentration is assignedmetic to averages a are model then computed grid(see for point Fig. all according samples to available its in the location. same Arith- latitude band true for POM which, as already pointed out in Sect. 5.2 Condensation nuclei This subsection evaluates the simulated number concentrations of condensation nu- seen in the right column, occuring mainly in the free troposphere. This is particularly IMPROVE (Interagency Monitoring of Protectedsity Visual of Environments) Miami and networks the is Univer- presented in Fig. port of condensable gasestion. The and near-surface the layers SOAin feature formation the marginal associated changes Polar with within Regions).concentrations against a tropical A the factor convec- comparision EMEP of of (European 1.5 Monitoring the (except and simulated Evaluation monthly Programme), mean surface mass 5 5 15 25 20 10 25 15 10 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ¨ a ¨ ¨ al om ), bring- we com- ˚ Heintzen- Angstr ciently de- 4.4 14 ffi Putaud et al. Heintzenberg et al. k), they derived the 14 erent seasons. In ad- ff ) are also shown. On the whole the ects in our model. reveals a clear increase in the number 11 ff 13 ), however, such modifications lead to pos- logitude) regions (Fig. 13 7568 7567 × i indicate a significant underestimate of particle ¨ , Fig. om parameters indicate that fine particles domi- 10 11 ects of modified aerosol nucleation and water uptake ˚ Angstr (latitude ff ) from measurements at six European surface sites (Har- ◦ and Fig. , bottom row). In summer, stronger solar radiation enhances 15 2 presents the geographical distribution of annual mean AOD × 2003 ◦ ( 11 the three-mode distribution functions derived by 15 , resulting in high concentrations of sulfuric acid gas in the near 2 13 ) with relatively large geographical coverage. Using measurements ob- and gas (cf. Fig. 4 Tunved et al. 2000 ¨ 12 om parameter (ANG) from the MODIS data. The largest AOD appears in the are the combined e ( erences between HAM2 and HAM1 shown in the middle and bottom rows SO ff 2 , second row). 15 ) dataset, due to the fact that the prescribed standard deviation (1.59 for both ) and 15 ˚ Angstr The di The top row of Fig. In Figs. For the marine boundary layer there exists a 30-yr climatology compiled by 2000 2003 parameterization, cloud microphysics, asdominated well regions there as is the a treatment marked of increase SOA. in AOD In and the decrease dust- in the The contrast isscheme less increases pronounced the in emissioning HAM2 flux the because HAM2 of results the the closerThe accumulation modified to simulated mode distribution observation, sea functions (cf. especially are salt in Sect. generally the emission broader middle than and the low latitudes. polluted areas and in regionsthe of storm high tracks. dust The loading, retrieved nate while medium the values aerosol are population seen overparticles over the are continents abundant and in overmodel the the reasonably polar reproduces storm these regions, tracks features while(Fig. of and coarse the in global the AOD and tropical ANG Atlantic. distributions Theof HAM2 Fig. pare this data setand (black curves) blue with curves). the Inized standard contrast by HAM1 well-defined to and and continental clearly HAM2 separatedis areas, simulations Aitken (red the correctly and accumulation remote captured mode. oceans This inthe feature are Aitken both character- mode model is versions. considerably higher In than HAM1 accumulation the mode number in all concentration latitude of bands. The ultimate goal of simulating aerosolson in climate. a climate In model this is subsection todetermine we understand the look their impact direct at the and simulated semi-direct aerosol aerosol radiative e properties that and and accumulation modes for 10 latitude bands (see Table 3 therein). In Fig. ( modes) is often larger than observed (typically 1.4–1.5). 5.4 Radiative properties of aerosols ( well, Hohenpeissenberg, Aspvretren and Isprain from 2000 1997 to and 2001, 2001)dition Pallas and are to Hyyti compared the standard withdiscussed HAM1 HAM in and simulations the HAM2 previous in subsection simulations, di (cf. the Fig. two sensitivity experiments model does a veryconcentration good at job these locations. in In reproducingpared winter, the all to HAM2 correct HAM1 simulations magnitude there are of verypossibly is similar. related aerosol a Com- to number slight enhanced shift particletion of of growth the H due distribution to functions changesthe towards in larger oxidation the sizes, surface of condensa- SO surface layers. Under such conditions, theation model results scheme. become Consistent sensitive with to the Fig. nucle- concentration of small particles whenthe kinetic figure), nucleation is and included a (solid moderateted green increase green lines when in lines). the Figure cluster activation scheme is used (dot- concentration in heavily pollutedare areas included. even In when the cleaner additional regions nucleation (Fig. mechanisms itive biases. This seems tois suggest that underestimated. the The regional reason gradienttheir might in aerosol be precursors, concentrations inaccuracies and/or in theor the model meteorological emission conditions. representation of So of aerosols far wetailed, aerosol and have consistent microphysics not and yet processes been accurate ablebiases. observational to Further data collect studies su to are help needed pinpoint to the address cause this of issue. these number concentration, geometric mean diameter and standard deviation of the Aitken berg et al. tained in a number of 15 5 5 25 15 20 10 10 15 25 20 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ects. ff c) fea- erences 18 ff c. Although 18 d–e), while there 18 f), resulting from the Bond and Bergstrom 15 ¨ om parameter that need ˚ Angstr ) (panel d) using the multi-model , HAM1 tends to produce very small 2 ¨ om parameter, Fig. 2009 − ( 10 ¨ . Daily mean model output is interpolated om parameter (Fig. × 17 ˚ Angstr 7569 7570 ¨ Kinne om parameters of small absolute value. provides a summary of the model performance b better centered along the diagonal. As for the ˚ Angstr 18 17 S there are singularities in the relative di ◦ ). The main contributors are black carbon and dust, ˚ Angstr E, 50–60 . For AOD the joint PDF of HAM2 vs HAM1 (Fig. ◦ 18 a) in the high latitudes. Such underestimates have been reduced in ¨ 18 om parameter where large positive values change abruptly into large neg- ). In the Southern Hemisphere storm track there are only small changes in shows the simulated annual mean global distribution (panels a–c) together . The AOD is further decomposed into contributions from aerosol water and ¨ 4.3 ˚ om parameter, the modified sea salt emission has reduced the number of cases http://aeronet.gsfc.nasa.gov Angstr ), which improves the simulated AAOD near the source regions (but not in remote 16 19 To have a closer look at the model results beyond annual mean, and compare them The magnitude and distribution of aerosol absorption optical depth (AAOD) are key These changes have brought the model results closer to the MODIS data, although 2006 ˚ Angstr of too large particles (small values of the is still a substantialto number be of improved cases in of the overestimated future. Figure there is a moderatecrease in increase aerosol in water. The the absorption dry AOD is AOD increased which by is a factor overcompensated of by 2 the from HAM1 de- (PDFs) shown in Fig. tures an elongatedresults shape from located the neara two the clear versions diagonal increase are ofbending of by the of and AOD diagram, the in large “cloud” indicating nearAERONET HAM2 similar. that the rarely On in bottom observed left the the AOD cornervalues other clean below of (Fig. hand, the regions 2 diagram there as inHAM2, is Fig. indicated making by the joint the PDF upward in Fig. 5.5 Aerosol radiative forcing The global meanFig. values of AODdry and mass. (In AAOD our in modeltions this HAM1 of diagnostic and calculation individual is components HAM2 performeddiagnosed and using are as AOD the of volume-weighted illustrated volume frac- attribution each in more mode.) of than The AOD. two In dry thirds both and of water versions, the AOD water total are makes AOD. up From HAM1 to the standard version of HAM2 ( scavenging that increases the lifetime of BC, and consequently thewith overall observation, BC we burden. use theof daily mean the data site of locations theto year is the 2000 presented sites from in AERONET. and A Fig. sampled map on the same days to derive the probability density functions at each of the AERONET site. rendering high values over thespatial pattern middle- is and well low-latitude representedatic continents. by both The underestimation HAM characteristic of versions, but AAODbeen with in a reduced HAM1 significant in system- over HAM2, thebeen partly whole changed because globe. according the The to refractive negative index the bias of medium-absorbing has black values carbon from (BC) has areas, e.g. the Arctic regions). The other reason for this improvement is the weaker wet median from the AeroCom projectgram and ( measurements from the NASA AERONET pro- Fig. with the reference result compiled by strong enough. The overestimation ofas AOD underestimation in over Eastern the US high-latitude andthe continental Central future. Europe, areas, A as needs further well to increase be of ANG addressed over in thefor storm atmospheric tracks absorption, is direct also aerosol desirable. and the semi-direct aerosol radiative e Near the region 60–140 of the ative values. This is because HAM1in simulated this a area large amount which of gave coarse negative mode particles there is still room forArabian improvement. Peninsula, In where Western dust China is and thebiases the dominant in Middle aerosol ANG East type, the and and model over negative still the biases has in positive AOD, suggesting the dust emissions are not yet ocean surfaces thecreased AOD aerosol and water particle amount(Sect. size as both a become consequence smaller, of reflecting the new theshift water de- of uptake size scheme distribution of the sea salt emission and reduced aerosol water uptake. parameter (suggesting increase in particle size). Over the middle- and low-latitude AOD but substantial increases in the 5 5 15 10 25 20 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) 2007 ect are , ff Lohmann O’Donnell ) Lohmann ects on cli- CLD), both ). Again we ff A2 1996 ( using from the Earth’s Lohmann et al. ff at the top of the atmosphere 2 , the aerosol size distribution − 5.4 . On the global scale the scatter- – ects are the water uptake scheme 20 ff 5.2 1.76 W m Lohmann and Roeckner − ects. Some of the model improvments, for ex- 7572 7571 ff , giving a sense of uncertainties in this quantity. 4 ) and by radioactive species e . The new parameterizations that have largest impact 5 ). The explicit treatment of SOA introduced by 2010 , and 4 2011 ) considerably reduces the aerosol water content in the lower , ) cloud microphysics parameterization, while the highest values of O aerosol nucleation scheme considers both neutral and charged 2 ) leads to an upward shift of the strongest nucleation to the tropi- 2011 ( /H Kazil et al. 4 1996 ( 2010 SO ( ) can be used to investigate, for instance, the impact of vegetation change 2 ). Zhang et al. WAT) and cloud microphysics (autoconversion, experiment HAM2 A2 2011 ( The modified sea salt emission calculation significantly changes the partitioning of By including all these updates in the model, we are able to obtain improved re- The impacts of these updates on the simulated aerosol distributions and properties For all the HAM2 simulations we have diagnosed the various components of aerosol and spatial-temporal variability simulated by HAM2 show better agreement with the particle number fluxes betweenshift accumulation of mode the andKazil size coarse et mode, distribution resulting al. to in smaller a particles. The nucleation parameterization of sults compared to HAM1. As shown in Sects. and Roeckner (1996), whichposition. Compared contributes to to HAM1, changesspecies aerosol except to lifetimes for are aerosol sea increased lifetime saltSOA, in (by and and HAM2 10–20 4 % wet % for for for de- allparticulate sulfate, dust). aerosol black organic Wet carbon, matter. deposition and is POA, decreased 107 for % all for aerosol species except for cal tropopause. Although the resultingmode changes number in concentration the are spatial nontrivial,relatively distribution the small of changes because nucleation in of the the direct small aerosol sizes e of the particles. are analyzed in Sects. on the global meanand AOD the new and stratiform aerosol cloudO’Donnell radiative microphysics. The et e water al. uptake scheme implemented by nucleation, which can be usedby to cosmic investigate the rays impact ( of nucleation from ions caused et al. on aerosol formation and thepling consequent to changes a in two-moment cloudmakes radiative stratiform it forcing. cloud possible The microphysics for cou- scheme thismate. ( model to directly simulate the aerosol indirect e This study introduces improvedECHAM-HAM aerosol model representations and in quantifiesglobal the their distribution, second impact and version direct on radiative of theample e the simulated in the aerosol sea properties, saltmodel and dust biases. emissions, were The directly others motivatedof by aimed the previously at aerosol noticed lifecycle having andthe a extending interactions more the between physically model’s various capability realisticThe in aerosol-related new representation consistently H micro- simulating and macro-scale processes. surface ( troposphere. The (global) totalAeroCom mass multi-model of mean. aerosol The waterautoconversion new is compared stratiform in to cloud closer the agreement scheme microphysics of with features weaker the HAM2 at TOA and at the Earth’s surface. 6 Conclusions ing of shortwave radiation(warming), (cooling) rendering overwhelms a the total absorption direct(TOA) forcing of of in longwave radiation standardstudy HAM2. exhibit The considerable various variationThe in parameterization the numbers schemes forcing, behind discussed as thesee can in a bar be this strong seen chart sensitivity from are the of given whiskers. the in model the result Appendix to (Table the water uptake scheme (experiment The lowest values (ofand total, Roeckner water and dry AOD) are all associated with the the total and water(Table AOD are from the simulation using theradiative old forcing water and uptake illustrated scheme the results in Fig. sitivity experiments discussed in Sect. to standard HAM2. For HAM2 the whiskers in the figure indicate the spread in the sen- 5 5 15 20 25 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ; Kul- ects ff 2004 , 7569 7585 , 7563 7548 , 2006. 7549 , 2000. Laakso et al. , 2011. , 2007. ) that takes into account 2009 ( ect on cloud via the first indirect ff ciency toward the Arctic: Sensitiv- ffi Croft et al. doi:10.1029/1999JD901161 doi:10.1080/02786820500421521 7574 7573 ) or by kinetic nucleation ( ect. It is worthwhile studying the indirect e 7547 doi:10.5194/acp-7-2503-2007 doi:10.5194/gmdd-4-3623-2011 ff 7548 2007 , , 2008. , 2011. ¨ om parameter, and the surface aerosol mass concentration data The authors thank U. Niemeier (MPI-M) for her comments on an earlier Riipinen et al. ) improve near-surface aerosol number concentrations in the polluted ; ), which may help achieve a treatment that is consistent with the cloud 2008 2006 , 2010 ( , ect and/or the second indirect e doi:10.1029/2010JD015096 of an improved shortwave radiationAtmos. Chem. scheme Phys., in 7, the 2503–2515, MAECHAM5 General Circulation Model, ity to aerosol scavenging and source regions, J. Geophys. Res., 116, D08213, T., Romakkaniemi, S., Kulmala, M.,crophysics and module Kokkola, SALSA implementation H.: in Evaluation ECHAM5-HAMModel of aerosol-climate Dev. the model, Discuss., Geosci. sectional 4, aerosol 3623–3690, mi- Review, Aerosol Sci. Technol., 40, 27–67, doi:10.5194/acp-8-6003-2008 and Ruedy, R.: MATRIXmicrophysical (Multiconfiguration module Aerosol for TRacker global of atmospheric models, mIXing Atmos. state): Chem. an Phys., aerosol 8, 6003–6035, types, J. Geophys. Res., 105, 6837–6844, In this study the evaluation was concentrated mainly on the global distribution and There are a few other modifications that have already been implemented in the model ff Cagnazzo, C., Manzini, E., Giorgetta, M. A., Forster, P. M. De F., and Morcrette, J. J.: Impact Bourgeois, Q. and Bey, I.: Pollution transport e Bond, T. C. and Bergstrom, R. W.: Light Absorption by Carbonaceous Particles: An Investigative Bergman, T., Kerminen, V.-M., Korhonen, H., Lehtinen, K. J., Makkonen, R., Arola, A., Mielonen, Bauer, S. E., Wright, D. L., Koch, D., Lewis, E. R., McGraw, R., Chang, L.-S., Schwartz, S. E., support by the FP6 project EUCAARI (Contract 34684). The service charges for thishave open been access covered publication by the Max Planck Society. References Abdul-Razzak, H. and Ghan, S. J.: A parameterization of aerosol activation - 2. multiple aerosol version of themodel. manuscript We and acknowledge M. the Esch NASA for Langley her Research support Center, in the coupling NCAR HAM Earth with Observing the ECHAM used in thisvery study. helpful The suggestions principal onAERONET investigators how Principal of to Investigators compare these andaerosol the measurements optical the data depth, campaigns AeroCom with Angstr provided used project model in for results. the We compiling model also and evaluation. thank J. providing Kazil, the D. the O’Donnell, and K. Zhang gratefully acknowledge the Acknowledgements. Laboratory, and the British Atmospheric Data Centre for providing the aircraft measurements microphysics in the model and reduce biases. figuration and resolution, notlations. only These will in be nudgedtion presented integrations, in scheme but separate used in papers.physically-based in “free” Furthermore, scheme this climate the has model aerosol simu- been activa- A version implemented new is and scheme still evaluation forCroft rather (Stier et the simple al. et in-cloud and al., aerosol empirical. 2012). scavenging A has more been developed recently by the radiative properties of aerosols.plemented, With it the is new possible two-momente to cloud investigate microphysics the im- aerosolof e anthropogenic aerosols on climate in our model and their sensitivity to model con- but not switched on in themala standard et HAM2. al. Aerosol formation byKuang et cluster al. activation ( of aerosol and collector sizesmore seem extensive to evaluation have is some still positive impact needed. on model results, but The remaining major model deficienciestracks, include (i) (ii) positive negative bias of biasgions, AOD of over and the AOD storm (iii) and negativeAitken aerosol mode, bias mass in of the concentration particle lower in troposphere number over high-latitude the concentration, re- heavily especially polluted that regions. of the regions, but would lead toof overestimation in the cleaner temperature-dependent continentaland regions. in-cloud The the scavenging inclusion below-cloud scheme scavenging scheme for of mixed-phase clouds observations. 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C., Coe, M., and Heimann, M.: Impact of 5 5 20 15 30 10 25 15 20 10 Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 5.5 5.5 – – 5.1 5.1 5.3 5.3 , , , , 4.6 4.7 4.1 4.1 4.2 4.3 4.4 4.5 4.6 4.6 4.7 4.7 4.1 4.1 – – Section number 4.1 4.1 ; , , - ) - 4 κ ). Kul- SO 2007 2010 2 ( 2011 , Kokkola Kulmala , ). Cagnazzo Kuang et al. Croft et al. ). ) and by ) ) formula for 2010 Lohmann et al. and , ). 2007 2002 O’Donnell et al. 1986 Kazil et al. ( ). Old schemes by , ( ) are still optional. 2009 cients for snow de- ( Petters and Kreiden- ffi Riipinen et al. 2008 ( 2010 ; O’Donnell et al. ); Complete removal of 1998 ). ( , ; Kazil et al. ). ¨ aki et al. 2006 2009 2007 ): Impaction scavenging coef- 4.4 ); Solar radiation scheme ex- 2007 , , ) or cluster activation ( ). , , ¨ Croft et al. ohler theory ( 2009 Verheggen et al. 2007 ( ficients for rain dependdistributions of on aerosols the and size tors; collec- The coe pend on aerosol size. Cheng et al. Optional scheme by East Asia soil properties updated by Option topendent use scavenging temperaturefor mixed-phase den- parameters based stratiform clouds on( a relationship from New scheme by as default,organic with nucleation based optional onnetic nucleation the theory H ki- ( 2008 et al. Kazil et al. Vehkam mala et al. 2011 Monahan et al. the radiusSect. range of 2–4 µm (see sulfuric acid gas fromsumed in the the air cloudy is partgrid of box as- ( a model The lifecycle of SOA is explicitlyulated; sim- Emissions ofcursors biogenic are pre- computedAnthropogenic interactively; precursor emissions are prescribed ( Two-moment stratiform cloud micro- physics scheme by ( et al. Concentration equation is solveda by two-step operator splitting scheme with analyticalduction and solution condensationet ( for al. pro- Considered for non-organic andganic or- aerosols,K based onweis the tended to six bands ( < T > T < Stier ) and ) ) and Zeleznik ) cients for Fouquart 2006 ffi ) ) as default 1966 1948 ( ( , cient for snow 2005 , ffi 2002 ). ) ( 2009 ( ) cloud microphysics without aerosol-cloud interaction 1980 ); Solar radiation 2005 Lohmann and Roeck- ) , ). , Zdanovskii Stier et al. ¨ aki et al. 1996 1996 ( 2005 Dentener et al. ), ( 2005 , 273 K, and ice cloud: , 7586 7585 Croft et al. Stier et al. 1991 rain; One fixed coe ( Scavenging parameters arescribed for pre- three ambientature temper- ranges273 K, (liquid mixed-phase cloud: cloud: 238K T < 238 K). Prescribed, mode dependentpaction im- scavenging coe Vehkam Smooth merging of emission func- tions in the particle radius2–4 range µm of ( Considered only foraerosols, non-organic based( on HAM1 specificsStratiformscheme cloud by ner microphysics scheme with four bands ( and Bonnel Concentration HAM2 specifics equation iswith solved three-stepator sequential splitting oper- stepping using scheme; explicit Nobetween time distinction cloudyparts of and a model cloud-free grid box. Stokes and Robinson is assumed to condenseately on immedi- existing aerosoland particles to haveto primary identical organic properties aerosolset ( al. SOA is approximatedmonoterpene as 15 % emissions of face at ( sur- , ) ) ) or Stier ) and 2002 ( Stier et al. 1998 ) ( 2002 ( 1986 ( erences between HAM1 and HAM2 in model configuration. 1998 ff ( ) Roeckner et al. ). ¨ aki et al. 2006a 2005 Lohmann and Roeckner Tegen et al. , , Monahan et al. scheme et al. Considered separatelyrain and snow for the Prescribed scavengingrameter pa- formode and each cloud type aerosol ( Smith and Harrison on Vehkam Kulmala et al. Dependent on thecompositions chemical of aerosol par- ticles andhumidity ambient (with respect relative toter). wa- HAM1 andfeatures HAM2 shared ECHAM5 ( 2003 transport,duction, chemical condensation,aerosol and nucleation. pro- Refractive indices of SOA are assumed the same asof those POA. Below-cloud scav- enging of aerosols Dust emission InteractiveIn-cloud calculation using scaveng- ing of aerosols Sea salt emission Interactive calculation based Aerosol nucleation Aerosol water uptake Atmosphericnamics and dy- physics Sulfuric acid gas Sources and sinks include Secondary organic aerosol (SOA) below-cloud wet scavenging scheme proposed by List of simulations presented in this paper. An overview of the main di CLD Same as HAM2 but with the H2SO4NUL Samecluster as HAM2 but with thekinetic old treatment for the SameOA sulfuric Same as as acid HAM2 HAM2 gas but but with equation with theWAT Same cluster old as activation nucleation HAM2 nucleation scheme but in andSS with the numerics kinetic forested for nucleation boundary the in layer sulfric theDU acid forested equation. Same boundary as Same layer HAM2 asBLCLD but HAM2 with but the with old the treatmentINCLD old with water-uptake organic Same scheme aerosol as Same HAM2INBLCLD as but HAM2 Same with but as the with HAM2 old the Same but sea Same below-cloud with as salt as wet the HAM2 emission HAM2 scavenging old but scheme but scheme with dust with proposed the emission the by modified scheme modified in-cloud in-cloud wet wet scavenging scavenging scheme scheme for for mixed-phase mixed-phase cloud cloud HAM2 SimulationHAM1 Description ECHAM-HAM version 1 as described by ( HAM2HAM2 HAM2 HAM2 HAM2 DefaultHAM2 configuration of ECHAM-HAM version 2HAM2 (this work) HAM2 HAM2 HAM2 HAM2 HAM2 Table 2. Table 1. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ¨ ohler -K κ HAM2 default HAM1 default 3 − κ 3 − cm 9 cm 10 11 × –10 –5 3 3 Concentration Note − − 4 cm cm listed in the rightmost column are SO 4 5 2 κ Observed Range of ), which were derived from the laboratory used in ECHAM-HAM2 for the κ 2007 ( κ 7588 7587 values of various organic compounds other than secondary organic Temperature Relative Humidity H κ Petters and Kreidenweis ) 230.15–305.15 K 0.01–100 % 10 ) 233–298 K 10–100 % (No constraint) 2002 Species SulfateSea saltPrimary organic aerosolSecondary organic aerosolBlack carbon 0.037 0.06Mineral dust 0.022–0.070 0.006–0.44 0.60 1.12 0.33–0.72 0 0.91–1.33 0 – – ( ) 180–320 K 1–101 % 10 1998 ( 2010 ( Values of the hygroscopicity parameter ¨ aki et al. Binary aerosol nucleation schemes available in ECHAM-HAM2 and their valid range Kulmala et al. Vehkam Kazil et al. theory based water uptake scheme. Thequoted observed from ranges of Table 1 in Table 4. measured growth factor ofis particle obtained radius. from For mean primary organic aerosols, the observed range aerosol. Table 3. of thermodynamical conditions. Boundary valuesdition are is used out in of case range. the actual atmospheric con- Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | , Textor 77 % 58 % 54 % 49 % 84 % 219 % 199 % ) Textor et al. , 2006 55 % 55 % ∗ ∗ ∗ ∗ 19.2 ) 4377 1235 Mean Std. Dev. AeroCom ( } } } Textor et al. 2006 4 % 4.1 43 % . 57 % 48 % 13 % 6.37 22 % 6280 13 % 19.20 40 % 12 % 25 % 18 % ff + SOA) 1.70 27 % SOA) SOA) 96.6SOA) 26 % SOA) 76.7 32 % 4.8 %8.0 % 1902 0.41 7.2 % 18403.1 % 607 49 % 54 % + + + + + + + + + + + + + − − + − 6.9 2.55 } AeroCom ( Mean Std. Dev. } 0.2 % (POA) 4.2 % (POA) 107 % (SOA) 6.54 27 % + + + Relative Di 9 % 0.67 25 % HAM2 vs HAM1 . 49 % (POA 3.5 % (POA 8.2 % (POA 3.1 % (POA 18 % 0.24 42 % 91 % 11 % 11 %19 % 7.12 33 % 16 % 4.12 18 % ff + + 8.5 % 7.0 % 9.35 31 % 8.6 % 59.74.8 % 8.8 % 22 % 7.9 % 3.7 % 9.4 % 52.8 22 % + + − + + − + + + + − − − − + − − 16 % (POA), + Relative Di HAM2 vs HAM1 erences. To put the numbers in perspective, the − 7590 7589 ff , 3.7 , 5.6 , 12.0 − SOA POA, SOA + −− − − HAM1 HAM2 HAM1 HAM2 POA ) 1 − ) ) 1 1 − − ) 1 − particle condensation 27.1 25.8 − 4 2 4 ) ) ) SO 1 1 1 Black carbon SO 2 − − − ) ) ) Dry deposition 0.59 0.64 Emissions 7.7 7.7 0.0 % 11.9 23 % SedimentationWet deposition 0.02 7.19 0.02 7.14 0.0 % TotalH 77.6 70.9 TotalSedimentation 1.62 77.3 1.56 70.5 Primary emissionsNucleation 2.3Aqueous oxidation 2.3 48.0Dry 0.11 deposition 42.5 0.21 Wet deposition 2.16 0.0 % 2.33 73.5 66.6 1 1 1 − − − Sinks (Tg yr Burden (Tg)Sources (Tg yr 0.11 0.13 Sources (Tg S yr Burden (Tg S) 0.78 0.85 Sinks (Tg S yr Lifetime (days)Aging time (days) 0.72 5.3 0.86 5.9 Lifetime (days) 3.7 4.4 ) are also listed. The standard deviations are given as percentages of the corre- Annual mean global mass budget of SU, BC, POM, SS and DU simulated by two ver- Continued. Sea salt Dust POM 2006 Sedimentation 1376 2038 Dry depositionWet deposition 948 2721 1484 2591 Emissions 5019 6110 Dry deposition 44.8 56.1 TotalSedimentationWet deposition 66.1 68.4 0.19 61.4 0.13, 0.06 43.9, 19.4 0.0 % (POA EmissionsSedimentation 751 289 805 341 Wet deposition 423 410 POA emissions 47.0 47.1, – SOA from monoterpenesSOA from isoprene Anthropogenic SOA emissions Dry deposition 19.1 4.9 3.3, 1.2 , Lifetime (days) 0.75 0.69 Sources (Tg yr Sinks (Tg yr Burden (Tg)Burden (Tg) 10.3Sources (Tg yr Sinks (Tg yr 11.6 Lifetime (days)Aging time (days) 10.3 11.6 5.0 4.8 5.2 5.4 Sources (Tg yr Burden (Tg) 0.99 0.83, 0.65 Lifetime (days)Aging time (days) 0.96 5.5 6.4 1.00, , 11.4 Sinks (Tg yr Table 5. multi-model mean and standard deviation of the AeroCom intercomparison project (from sion of the HAM model and their relative di Table 5. sponding mean values. Theand AeroCom sedimentation. dry For sea deposition salt listedWe there therefore here is cite is one the the outlier multi-modelsalt model sum budget. median which of (indicated features dry by very asterisks) deposition high instead emissions. of mean for the sea et al. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | 4.7 ), while . 9 1996 ( ). See Sects. 2007 . ( ff 22 % 17 % 13 % 8.5 % 4.0 % 107 % + + + + + + Lohmann et al. Lohmann and Roeckner 20 Jun–15 Jul 2008 23 Jun–13 Jul 2008 for evaluating the simulated concentration W 8 Aug–7 Sept 2007 NCAR EOL EE 31 Oct–23 Dec 1991 31 Mar–5 May 2001 NCAR EOL NCAR EOL W 29 Apr–25 May 2007 NCAR EOL W 31 Aug–7 Oct 1996 NASA LaRC W 27 Feb–10 Apr 2001 NASA LaRC ◦ W 3 Apr–22 AprW 2008 1 Apr–21 Apr 2008 NASA LaRC NASA LaRC W 5 Aug–7 Sept 2007 NASA LaRC W 4 Mar–15 May 2006 NASA LaRC W 28 Feb–29 Mar 2006 NCAR EOL W 16 Aug–27 Sep 1996 W 12 Mar–12 Apr 1999 ◦ ◦ ◦ ◦ ◦ W 5 Mar–16 May 2006 W 7 Mar–19 Apr 1999 NASA LaRC W 25 Feb–11 Apr 2001 ◦ ◦ ◦ ◦ ◦ ◦ ◦ W 24 Dec 2004–24 Jan 2005 NCAR EOL W 15 Oct–15 Nov 2008 NCAR EOL 5.2 ◦ ◦ ◦ E 16 Feb–24 Mar 1999 NCAR EOL ◦ ◦ E 13 Jul–14 Aug 2004 BADC ◦ ◦ Aerosol lifetime E–180 E–170 W–37 W–69 W–36 W–89 E–86 W–88 E–105 W–153 E–109 W–77 E–85 W–76 E–118 E–75 ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ E–85 W–0 W–57 W–70 ◦ ◦ ◦ ◦ 7592 7591 CLD HAM2 Relative di N 65 ◦ NN 100 169 N 164 N 140 N 141 N 175 NN 40 106 N 136 NN 72 113 S 100 N 152 N 165 N 148 N 166 S 90 ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ N 111 ◦ ◦ ◦ ◦ ◦ ◦ ◦ N 160 HAM2 ◦ S–30 N–50 N–90 N–81 S–17.5 N–53 N–53 N–53 N–52 N–40 N–60 S–45 S–39 S–35 S–40 N–21 N–46 S–15 ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ ◦ N–3 N–41 ◦ ◦ Range Range coverage CLD uses the scheme of particle 3.6 4.4 DC-8 16 P3-B 35 P3-B 21 P3-B 6 − 2 4 1 Dust 5.0 5.2 SOASea saltBlack carbonPOA 5.2 0.59 5.5 0.69 5.9 11.4 5.9 6.4 SO MILAGRO C-130 16 PACDEX HIAPER 20 PASE C-130 1 TRACE-P DC-8 13 VOCALS C-130 30 FieldCampaign ACE-1 Platform Latitude C-130 70 Lontitude Temporal Source ACE-ASIAARCTAS C-130ARCTAS DC-8 10 INDOEX P3-B 32 C-130 32 10 INTEX-A DC-8 27 INTEX-B C-130 16 ITOP BAE-146 33 PEM-Tropics A DC-8 72 PEM-Tropics B DC-8 36 RICO C-130 15 List of observational data used in Sect. Impact of cloud microphysics parameterization on aerosol lifetime (unit: day). The for further details. 5.1 Table A1. of condensation nuclei. The measurementsMarine campaigns Aerosol Characterization include: Experiment), ACE-1 ACE-ASIA (Southern (Asianacterization Pacific Hemisphere Regional Experiment), Aerosol ARCTAS Char- (Research ofcraft the and Composition Satellites), of INDOEX the (IndianTransport Troposphere Ocean from Experiment Experiment), Air- – INTEX-A Phase (Intercontinental– Chemical A), Phase INTEX-B B), (Intercontinental ITOP ChemicalEXperiment), (International Transport RICO Experiment Transport (Rain of in Ozonemosphere Cumulus and Land Over Precursors), Study), the PACDEX (PACific PASEcific Ocean), Dust (Pacific Exploratory VOCALS Atmospheric Missions (VAMOS Tropics Sulfur Ocean A),TRACE-P Experiment), Cloud PEM-Tropics (TRAnsport B At- PEM-Tropics and (Pacific A Exploratory Chemicalthe (Pa- Missions Evolution NASA Tropics LaRC over B), Airborne the ScienceNational Pacific). Data Center The for for data Atmospheric Atmospheric are Composition ResearchBritish program Earth obtained Atmospheric (NASA Data Observing from LaRC), Centre Laboratory (BADC). (NCAR The EOL), aircraft and trajectories the are shown in Fig. Table 6. sensitivity experiment HAM2 and the standard ECHAM-HAM2 model uses the scheme of Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | SFC all IS1 TOA clear ect, ff FLW ; top-of- SFC clear SFC all FLW m μ TOA all = 2.0 , surface clear-sky σ r < 0.5 FLW stand for the optical and FSW stands for the number TOA all d SU BC POA DU SS SOA_IS1 SOA_IS2 SOA_MO1 SOA_MO2 SOA_ANT r TOA clear SFC clear m μ FLW 0.37 0.23 1.40 0.83 0.45 0.24 1.94 0.91 MO2), and from the oxidation and FLW and AOD SFC all w DU DU = 1.59 3.81 0.32 0.20 1.32 0.78 4.09 3.14 0.24 0.15 1.11 0.70 3.863.833.80 0.313.79 0.333.89 0.32 0.203.59 0.32 0.203.80 0.203.97 1.21 0.30 0.203.66 1.32 0.32 1.32 0.34 0.76 0.193.86 1.32 0.29 0.78 0.20 0.78 0.21 1.31 0.31 0.78 0.19 1.31 1.45 0.78 0.20 1.17 0.78 0.85 1.21 0.74 0.76 σ m < r < 0.5 TOA clear FSW − − − − − − − − − − − − − μ SU BC POA DU SS SOA_IS1 SOA_IS2 SOA_MO1 SOA_MO2 SOA_ANT 0.05 SFC clear . Numbers given in bold are the larges and 5.76 6.20 4.72 5.71 5.83 5.76 5.77 6.31 5.40 5.74 6.03 5.42 5.71 m MO1 and SOA FSW − − − − − − − − − − − − − μ SFC all erent products from isoprene oxidation (SOA TOA all 7594 7593 ff 1.96 2.07 1.59 1.94 1.98 1.95 1.94 2.03 1.85 1.95 2.12 1.86 1.94 = 1.59 FSW − − − − − − − − − − − − − σ m < r < 0.05 BC POA SU BC POA μ Aitken Mode Accumulation Mode Coarse Mode and FLW SOA_IS1 SOA_IS2 SOA_MO1 SOA_MO2 SOA_ANT SOA_IS1 SOA_IS2 SOA_MO1 SOA_MO2 SOA_ANT TOA clear 0.005 ANT). As for the mode parameters, 3.79 3.69 3.86 3.80 3.81 3.54 3.78 4.06 3.52 3.69 4.08 3.06 4.33 SFC clear FSW − − − − − − − − − − − − − d m μ ). The chemical compositions include sulfate (SU), black carbon AOD 0.044 0.041 SU = 1.59 w σ 2005 ( r < 0.005 the prescribed standard deviation. Nucleation Mode σ AOD AOD 0.109 0.074 0.034 0.163 0.123 ; surface clear-sky and all-sky shortwave forcing FSW Aerosol optical depth (AOD, unitless) and aerosol radiative forcing (direct e ) in simulations discussed in this paper. AOD Stier et al. 2 TOA all IS2), from monoterpene oxidation (SOA − Soluble Insoluble Aerosol modes and compositions considered in HAM2. Adapted and updated from CLD H2SO4NUL 0.130cluster 0.089kinetic 0.137 0.041 WAT 0.135 0.096OA 0.094 0.135DU 0.041 0.095 0.041 SS 0.040 BLCLD 0.131INCLD 0.089 0.134 0.124INBLCLD 0.094 0.139 0.042 0.085 0.130 0.145 0.098 0.040 0.039 0.089 0.101 0.041 0.041 HAM2 0.135 0.094 0.041 HAM2 HAM2 HAM2 HAM2 HAM2 HAM2 HAM2 HAM2 HAM2 HAM2 HAM2 HAM2 (BC), primary organic aerosol (POA),aerosol mineral (SOA). dust SOA is (DU), further sea divided salt into (SS), di and secondary organic and SOA of anthropogenic precursors (SOA Fig. 1. Table 1 in depth associated with aerosolsented water in and dry components: mass, top-of-atmosphereand respectively. clear-sky The FSW radiative and forcing all-sky is shortwave pre- forcing FSW median radius, and unit: W m atmosphere clear-sky and all-sky longwave forcing FLW Table A2. smallest values among the sensitivity experiments carried out with HAM2. and all-sky longwave forcing FLW Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) erent 2002 ff ( ¨ aki et al. Vehkam ) nucleation scheme but the old ) SOA submodel switched on); The erence between the two simulations 2010 OA that uses the old (HAM1) simple ( ff NUL” uses the 2011 ( . All other aspects of model configuration are ); The di ). The three columns correspond to di 4 3 Kazil et al. − ); “HAM2 SO 7596 7595 2005 2 , 4.1 ). The middle panel shows results from the standard 3 STP (1013.25 hPa, 273.15 K) ] and mass concentration − 3 − O’Donnell et al. Stier et al. H2SO4” uses the and 4.2 . equation (cf. Sect. 4 (c) SO 2 gas (lower row, unit: molecules cm 4 Temporal and zonal mean vertical cross-sections of the mass concentration of partic- and zonal mean vertical cross-sections of the number concentration of nucleation mode SO 2 Fig. 3. ulate organic matter (POM) (unit: µg m left panel corresponds to a sensitivity experiment HAM2 is indicated in panel handling of the H ECHAM-HAM2 model (i.e., with the SOA scheme (see Sect. identical in the three simulations. of H parameterization and the old treatment of H particles [upper row, unit: particles cm Fig. 2. simulations, as indicated byHAM2 configuration; the “HAM2 title of each panel: “HAM2” refers to the standard ECHAM- Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) 1 − s 2 Mona- − the resulting changes in aerosol erent implementations of the (c) ff corresponding relative changes in the mass ) sea salt emission schemes. The blue curves (b) ), given by di 7598 7597 1 1998 − ( Smith and Harrison ) and erence of annual mean mass flux; ff 1986 Relative changes in dust emission due to modified soil properties in East Asia, given ( Accumulation mode and coarse mode sea salt aerosol number fluxes (unit: m Fig. 5. (a) as relative di concentration of dust aerosolsoptical in depth the (AOD). lowest model layer; as functions of 10-m wind speed (unit: m s Fig. 4. han et al. correspond to the the old (HAM1) version, and red the new (HAM2) version. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) in the INCLD, 2009 ( Lohmann and ect of modified ff Croft et al. ) simulated with the standard 2 − The combined e (c) for further details. erences in annual mean liquid water ff 4.7 di (c) ) are identical in all other aspects of model 2 7600 7599 Changes due to modifications by (b) CLD using the old cloud microphysics scheme ( erences in shortwave cloud radiative forcing between HAM2 and ff for further details. INBLCLD, cf. Table di 4.6 (b) ) and without aerosol activation; ) between the two experiments. See Sect. 1996 2 Changes in annual mean AOD caused by modification in the in-cloud scavenging of Annual mean shortwave cloud radiative forcing (W m , − BLCLD and HAM2 path (g m Roeckner Fig. 7. (a) in-cloud and below-cloud scavenging. The four experiments shown here (HAM2, HAM2 ECHAM-HAM2 model; below-cloud (rain and snow) scavenging parameterization. HAM2 configuration. See Sect. a sensitivity experiment HAM2 mixed-phase stratiform clouds; Fig. 6. (a) Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ) 3 − of the A1 7602 7601 . Further details of the campaigns are listed in Table 11 and 10 and Figs. 5.2 Annual and zonal mean cross-sections of aerosol mass concentration (unit: µg m Aircraft trajectories of the condensation nuclei measurements used for model evaluation in Sect. Fig. 9. Appendix. Fig. 8. simulated by HAM1 (left column) and HAM2 (middle column), and the ratio (right column). Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | STP 3 Kulmala − . Model results are derived for further details. 9 5.2 and Fig. A1 ). See Sect. erent regions. The observational data are com- ff 2010 for further details. 7604 7603 , 5.2 Kazil et al. ; ). The lower panel uses a cluster nucleation scheme ( 2007 , 2008 ( and an organic compound. The upper panel uses the kinetic nucleation 4 SO 2 Riipinen et al. Kuang et al. STP (1013.25 hPa, 273.15 K) ] in di ; Vertical distribution of condensation nuclei concentrations [unit: cm 3 Vertical distribution of simulated and observed condensation nuclei concentrations − dry diameter (0.01 µm). See Sect. 2006 ff , Fig. 11. et al. piled from campaign measurements shown in Table (1013.25 hPa, 273.15 K)] inditional Northern parameterization switched Hemisphere on midlatitudes,nucleation in simulated of the by planetary H HAM2 boundary layer with to ad- take into account the scheme of Fig. 10. [unit: cm from daily mean outputconcentration is of calculated the by integrating months thecut-o simulated in number which size distribution the above the measurements lower were obtained. Model CN Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ). 2003 ( Tunved et al. ) and 2003 ( Putaud et al. 7606 7605 but for boreal summer (June-July-August). 12 Comparison of the simulated and measured aerosol size distributions in the planetary As in Fig. Fig. 13. Fig. 12. boundary layer over land in borealare winter (December-January-February). the The observed thick median black curves size distributions from Model results (the colored0.8 µm curves) because are this is plotted thelines only range underlie measured for solid in the color the references. diameter lines. Note range that most between parts 0.01 of and the dotted Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | in each panel are the 2 ¨ σ om parameter is retrieved and ˚ 1 Angstr σ ). The simulations shown in red and blue cor- 7608 7607 2000 ( erences between HAM2 and HAM1 results (third and bottom ff Heintzenberg et al. ¨ om parameter (ANG, right column) from the MODIS retrieval (top row), simulated by , compiled by Comparison of the measured (black curves) and simulated (colored curves) size dis- Geographical distribution of the annual mean aerosol optical depth (AOD, left column) (k) ˚ Angstr HAM2 (second row), androws). the The di displayed satellitelated/retrieved retrievals at are mid-visible multi-year wavelength 0.55 mean µm.using The fields. the MODIS The wavelengths AOD 0.55 fields µmland. are and The calcu- model-simulated 0.865 µm ANG over isall the grid calculated points. using ocean, the and wavelengths 0.47 0.55 µm µm and and 0.66 0.825 µm µm at over Fig. 15. and Fig. 14. tribution functions of the Aitkenboundary and layer. accumulation The modes observations (solublepanel are and a insoluble) 30-yr in climatology the covering marine the brown boxes shown in respond to the HAM1observed standard and deviation HAM2 of simulations,value the of respectively. Aitken 1.59 and is accumulation prescribed mode. for In both modes. the HAM model a fixed Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | . At 18 erences (bottom left panel), and the refer- ff 7610 7609 for further details. 5.4 ¨ om parameter (ANG) of the year 2000 are used for the comparison in Fig. Geographical distribution of the annual mean aerosol absorption optical depth (AAOD) Map showing the AERONET sites at which the daily mean aerosol optical depth (AOD) ˚ Angstr and Fig. 17. each site the rootments mean is square computed error forresults (RMSE, both of in the daily HAM2 HAM1 meanresults and (reduced AOD for HAM2 or RMSE) both simulaitons. ANG) for parameters; Green againstresults both Empty dots are measure- obtained. indicate triangles AOD See improved and and Sect. rectangles ANG; mark Orange the dots locations indicate where mixed degraded Fig. 16. simulated by HAM1 andence HAM2 result compiled (top by row), S.adjusted their Kinne with di (bottom AERONET measurements. right panel) using the AeroCom multi-model median Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | for further de- erent scale (see , the AERONET- ff 5.4 (a) cient and root mean ffi and model output (also 17 7612 7611 ¨ om parameter (lower row). The color shading shows the joint proba- . Note that the absorption AOD is displayed with a di 2 ˚ Angstr erence of the two data series. ff Comparison of the AERONET-retrieved and model-simulated aerosol optical depth Global and annual mean aerosol optical depth simulated by HAM1 and HAM2, the the y-axis on the right, in orange). Fig. 19. corresponding contributions from aerosol waterWhiskers and associated dry with mass, the asiments HAM2 well results listed as indicate in the the Table absorption ranges AOD. given by the sensitivity exper- retrieved and HAM1 simulatedfrom AOD, AERONET computed for the from year the 2000 daily at mean all measurement locations indicated retrieved in Fig. bility density distribution (unit: %) as a function of, for example in panel Fig. 18. (upper row) and daily means) sampled attails. the The same R time and instances RMS and values locations. noted in See each Sect. panel are the correlation coe square di Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | ect simulated by HAM2 at top of the ff 7614 7613 . 2 Caption on next page. Global and annual mean aerosol direct radiative e Fig. A1. atmosphere (TOA) and at thesensitivity Earth’s experiments surface. in Whiskers Table indicate the spread among the HAM2 Fig. 20. Discussion Paper | Discussion Paper | Discussion Paper | Discussion Paper | (d) ), in this com- 2005 cient between sim- ( ), green crosses the ffi particulate organic matter, Stier et al. (c) black carbon, 7615 (b) http://vista.cira.colostate.edu/improve/ ), and brown circles the University of Miami network (data sulfate, (a) ) of erent from the actual altitude of the measurement, so as to ensure 3 ff − dust. The solid lines indicate the 1:1 ratio. The dashed (and dotted) lines http://www.emep.int (e) Scatter plot comparing the observed and HAM2-simulated monthly mean surface mass comparability. parison we have only includedlayer the is stations at less which than the 200 geopotential m height di of the lowest model EMEP network ( by courtesy of J.values Prospero). from Data remote from marinemean. the sites, When while University comparing of the themodel-calculated simulated IMPROVE Miami daily and concentrations are mean with EMEP values multi-year observations are datathen monthly sampled in are averaged mean on the over available the year each as same 2000,we days month. daily the as also To the increase use measurements BC the and simulations and amount are POM of nudged data measurements to of in theing the the year to years 2000, evaluation, measurement 2002 the time and temporal isfrom 2003 sampling skipped all from of in model daily EMEP. this time Considering model case. steps that output The in our accord- simulated the monthly month. means Furthermore, are following computed concentrations (unit: µg m Fig. A1. sea salt, and indicate domains in thevations diagram within in a which factorin the of agreement simulated 2 within concentrations (and a agree 5).ulation with factor Also and of the shown observation in 2 obser- (the eachcollected (the R-value). in panel P2 Blue the are value), IMPROVE squares network the and indicate percentage the ( comparison of correlation with samples coe measurements