A change in atmosphere

A longstanding and fruitful collaboration between Professor Jeffrey Forbes and Dr Maura Hagan has led to several exciting breakthroughs in the burgeoning field of research

© CU © Carlye Calvin scale wave model (GSWM) and made the results widely available to the space physics community. More recently, I focused my attention on the NCAR 3D first-principles upper atmospheric general circulation models to further explore tidal and planetary wave impacts on the atmosphere and in collaboration with NCAR colleagues, graduate students and postdoctoral fellows.

In what ways has your research contributed to a greater understanding of these atmospheric interactions? PROFESSOR JEFFREY FORBES & DR MAURA HAGAN PROFESSOR JF&MH: Our research has created a new level of understanding as to how processes in the lower atmosphere drive How did you both become interested in disturbance, and investigated the impacts variability in the upper atmosphere space weather? of this variability on our ability to predict and ionosphere through the impacts of satellite ephemerides. All of these interests vertically propagating atmospheric tides JF: I was first introduced to atmospheric are still reflected in the research that I and planetary waves. Our model results tides by Professor Marvin Geller while perform today. have provided a context within which many pursuing my MSc at the University of observations of atmosphere and ionosphere Illinois in 1969. He had recently completed MH: Forbes introduced me to the field variability have been interpreted. In his PhD on the lunar at of atmospheric tidal research while I was addition, we have analysed many ground- the Massachusetts Institute of Technology attending graduate school at Boston and space-based observations to validate (MIT), and we collaborated on a paper College. I conducted thesis research with existing models and to provide direction for concerning the effects of the lunar tide a simple tidal model in pursuit of my further model development. on optical emissions from the upper MSc. My PhD and postgraduate work atmosphere. I then moved on to pursue included diagnosing and interpreting upper How do your skills and experiences my PhD at Harvard, where my advisor was atmospheric tidal signatures in incoherent enable the successful running of the Professor Richard S Lindzen, a leader in the scatter radar measurements made at MIT programme? development of atmospheric tidal theory Haystack Observatory. and models. JF: Our joint collaboration has been fruitful When I came to the National Center for and synergistic. While Hagan has devoted During the 1970s, my military service at Atmospheric Research (NCAR) some herself to the development and application the Air Force Research Laboratory involved 20 years ago, I shifted my focus to the of increasingly sophisticated models, I research into space weather effects of development of numerical tidal and have primarily concentrated on analyses solar origin on the atmospheric drag on planetary wave models. Between 1993 and of satellite-based measurements. This type satellites. I performed scientific studies 2003, I collaborated with Forbes to develop of model-measurement interplay is at the on the variability of drag due to solar increasingly robust versions of the global- heart of advancing our science.

64 INTERNATIONAL INNOVATION PROFESSOR JEFFREY FORBES & DR MAURA HAGAN

Would you discuss some of the outcomes and applications of your work?

MH: The research we perform is basic, without any immediate applications in mind, though we are aware that our work adds to the knowledge base required to build predictive space weather infrastructure to support operational applications. Rising tides However, there are occasions where it is possible to demonstrate the practical impacts of our work. One of Forbes’s students, for example, demonstrated how upper atmosphere density variations produced by the atmospheric tidal spectrum significantly affect uncertainties in the surface impact location of objects re-entering the atmosphere from space. A similar project to assess tidal effects Researchers based on aerobraking at Mars is ongoing. at the University of What have been the project’s greatest Colorado and the National Center successes? for Atmospheric Research are combining their JF&MH: Our most significant achievement has respective expertise in data analysis and modelling to been demonstrating that troposphere variability shed new light on space weather, with a particular emphasis on how is a significant driver for upper atmosphere and ionosphere space weather. This vertical atmospheric tides affect conditions in the Earth’s upper atmosphere transfer is accomplished through the upward propagation of atmospheric tides and other THE EXISTENCE OF space weather and the ways feed into each other organically: Hagan’s models waves. After almost a decade of developing in which it could impact Earth is a relatively new offer a physical representation of the data Forbes GSWM, we were in a position in 2002-03 to topic among scientists. Adverse events caused by studies, while Forbes can provide insight into the predict the upper atmosphere response to these phenomena could have worrying implications reliability of Hagan’s models and suggest potential realistic lower atmosphere tidal forcing. In for life on Earth. Broadly speaking, space weather improvements for future versions. particular, we focused on the spatial-temporal covers a wide range of environmental conditions distribution of latent heating released in present on the Sun, throughout space and in the UNDERSTANDING ATMOSPHERIC TIDES tropical convective clouds, and how the upper Earth’s magnetic field and upper atmosphere. From atmosphere responds to this forcing. solar flares to geomagnetic storms and coronal Forbes and Hagan aim to learn more about the mass ejections, different types of space weather impact of space weather of the Earth’s upper Over the following decade, and continuing have the potential to seriously impact technological atmosphere – the . Research within today, there has been an explosion of systems based both on the ground and in space. their field has established three main factors that publications that interpret observations in lead to its varying conditions: the absorption terms of the spectrum of waves that our Among the vital pieces of infrastructure that of solar extreme ultraviolet radiation into the study predicted. We brought increasingly can be interrupted by space weather are thermosphere; the reprocessing of solar wind sophisticated models to this problem, and satellite operations, electric power distribution energy as electric fields, currents and particles now address nonlinear tide-tide interactions; grids, communications, aviation, navigation that enter the thermosphere; and the upward ionospheric effects; and modification of the and emergency response systems. Given that propagation of waves produced in the lower regions wind circulations and electric fields, thermal our society is increasingly dependent on these of the Earth’s atmosphere. structure and plasma and neutral densities technologies, a severe spate of space weather that result from tidal dissipation. Throughout could potentially damage our health, security and While the pair and their colleagues have worked this work, we have extensively used satellite economy. Therefore, a deeper understanding of the extensively on all three of these sources, they are observations to define the tidal forcing and factors that lead to such occurrences is becoming currently most excited about the latter: “Within provide verification of model predictions. increasingly important, as is the ability to make the last decade a new realisation has arrived on more accurate predictions. the scene of ionosphere-thermosphere science: terrestrial weather significantly influences space weather,” Forbes enthuses. As key players in this A UNIQUE RESEARCH PARTNERSHIP emerging research area, Forbes and Hagan are For over 30 years, Professor Jeffrey Forbes of particularly interested in the role that atmospheric the University of Colorado has been conducting tides play in the variability of space weather pioneering investigations into space weather conditions in the Earth’s upper atmosphere. in collaboration with his colleague Dr Maura Through their research, they are pushing to explain Hagan from the National Center for Atmospheric how upward propagating solar and lunar tides and Research (NCAR). planetary waves transfer energy from the lower atmosphere to the thermosphere, specifically at The individual skills that Forbes and Hagan bring altitudes between 100 km and 500 km. to their partnership are key to its success. While Forbes’s expertise lies primarily in analysis of COMPARING EARTH AND MARS data obtained from a range of satellites, Hagan focuses on the development and application The researchers are currently working on an of intricate models. Both of these components innovative series of comparative studies for the WWW.RESEARCHMEDIA.EU 65 PROFESSOR JEFFREY FORBES & DR MAURA HAGAN

tides that spread into The group hypothesises that the upward An artist’s depiction of the CHAMP satellite. © ESA the upper atmosphere propagation of waves into the upper atmosphere and ionosphere. is linked to the density and winds in a given ambient environment. Moreover, they are keen to Forbes leads on the ascertain the outcome of forcing from the lower work conducted on atmosphere when the environment is changed Mars, which, similar by another key factor, such as an increase in solar to their work on radiation. In addition, the team hopes to discover Earth, is concerned whether a particular ambient environment’s 1982-88 with the reaction of reaction to tides and planetary waves has any 1993-95 its upper atmosphere bearing on the upper atmospheric and ionospheric Forbes and Hagan use 1D and The researchers perform a to both variations in responses to solar geomagnetic storms. 2D tidal models to investigate the Sun’s radiation effects of molecular diffusion, collaborative examination of and waves originating composition and mean winds two- and 16-day planetary PLANS FOR THE FUTURE from below. So far, on the vertical propagation waves with a 2D tidal the researchers have As well as continuing to pursue a wide range of tides model successfully identified of projects, Forbes and Hagan have plans 1995 and modelled a series for other research endeavours, with new of upper atmosphere mission developments promising extended Hagan develops the first waves observed by data to analyse. For example, the recently version of the global-scale planetary atmospheres of Earth and Mars, citing the Mars Global Surveyor satellite and linked launched European Space Agency (ESA) Swarm 1997 wave model (GSWM) that the two planets are sufficiently similar them to Mars’s surface topology. In addition, mission, which comprises three satellites with using the 2D model as and different to one another to provide unique Forbes has assessed the drag on satellites on accelerometers and other instruments, will The pair uses 1D and 2D a blueprint and useful insights. While the main motivation Earth and Mars in collaboration with Dr Sean gather pole-to-pole measurements of neutral models to estimate upper of furthering understanding of Earth’s upper Bruinsma, to measure their upper atmosphere densities, winds and electric and magnetic fields. atmosphere tides generated atmosphere is to learn how to improve the responses to 27-day and 11-year variations in by latent heat release in resilience of radio signals used in navigation solar flux. In addition, NASA’s Ionospheric Connections 2000-02 deep convective clouds and communications systems to environmental (ICON) mission – due for launch in February interference, research conducted on Mars is 2017 – will obtain similar data to Swarm, but Together, Forbes and INTERACTION BETWEEN DRIVERS particularly valuable in enhancing the accuracy of at lower altitudes and latitudes, as well as Hagan adapt Hagan’s aerobraking operations. Alongside their goal to reveal more about how measurements of ionospheric emissions and GSWM for Mars terrestrial weather can impact environmental chemical composition. At the same time, NASA observations Within their studies of Earth, land-sea conditions in the Earth’s atmosphere, Forbes, will launch the Global-scale Observations of 2010-13 differences are among Forbes and Hagan’s Hagan and their fellow researchers are also the Limb and Disk (GOLD) mission, which will primary interests. This phenomenon alters the interested in ascertaining the ways in which this measure densities and temperatures of Earth’s Forbes uses the Challenging latitude and longitude distribution of tropical source of space weather interacts with solar- upper atmosphere. “These missions will add to our 2008 Minisatellite Payload (CHAMP) and deep convection, giving rise to latent heat and geomagnetic-driven varieties. In this area, knowledge by enabling studies of the interactions Hagan becomes Gravity Recovery and Climate release in clouds. Given that this process runs they hope to determine whether the upper between the neutral and ionised components of Deputy Director Experiment (GRACE) satellites’ on a diurnal cycle, it leads to a range of periodic atmosphere operates in a linear way. the upper atmosphere,” Forbes explains. of NCAR density measurements to delineate solar and lunar tides 2001-03 in the thermosphere AN UNPRECEDENTED RESEARCH OPPORTUNITY The researchers publish important papers based on In 2012, Forbes, Hagan, Drs Xiaoli Zhang and Gang Lu were awarded NASA funding to become Participating GSWM-02 findings that link latent heat release in deep convective Investigators on the Gravity Field and Steady-State Ocean Circulation Explorer satellite mission clouds to upper atmosphere THE ESA-administered Gravity Field and Steady- largely because its accelerometers were able to caused by lower atmosphere topographic and tides and tidal variability State Ocean Circulation Explorer (GOCE) satellite, take extensive continuous measurements of pole- convective sources, disturbances originating in the launched in March 2009, completed its mission in to-pole densities and winds at a low orbital altitude polar regions and local and global responses to October 2013. During its time in orbit, the satellite of 260 km – a previously unprecedented feat. geomagnetic disturbances. Over the course of the took a series of high-resolution measurements of project, the team also hopes to tackle hemispheric Earth’s gravity field. GOCE was equipped with an The team plans to use GOCE data alongside those asymmetries, solar flares and planetary waves, and electric ion thruster that balanced out any drag it of the Challenging Minisatellite Payload (CHAMP) to establish the relationships between the space encountered whilst in orbit, and it was in a closed- Gravity Recovery and Climate Experiment (GRACE) weather variations caused by solar, geomagnetic loop system with its three pairs of three-axis, servo- satellites and NCAR simulations in order to gain a and terrestrial meteorological forces. controlled, capacitive accelerometers to promote a better picture of thermosphere space weather. drag-free environment. To date, Forbes, Hagan and their co-workers have Now that the GOCE mission has finished, scientists used these data to study the variability of solar around the world are poring over the data it and lunar tides, small-scale waves has gathered in order to establish a clearer idea of Earth’s properties. Among these researchers are Forbes and Hagan, who are both part of a University of Colorado and NCAR joint project, which aims to investigate the space weather of the thermosphere. Forbes and his colleagues saw GOCE as a particularly attractive research opportunity, An artist’s depiction of the GOCE satellite. © ESA

66 INTERNATIONAL INNOVATION Research timeline INTELLIGENCE SPACE WEATHER LINKED Highlights of Forbes and Hagan’s research TO TERRESTRIAL WEATHER collaboration, spanning more than 30 years OBJECTIVES • To elucidate and understand how lower atmosphere processes and variability affect space weather in the upper 1982-88 atmosphere, including both the 1993-95 ionosphere and thermosphere Forbes and Hagan use 1D and • To establish how the response to this source of 2D tidal models to investigate The researchers perform a space weather interplays with that due to solar- and geomagnetic-driven variability effects of molecular diffusion, collaborative examination of composition and mean winds two- and 16-day planetary KEY COLLABORATORS waves with a 2D tidal on the vertical propagation Dr Sean L Bruinsma, Centre National d’Etudes of tides model Spatiales (CNES), France • Dr Astrid Maute, 1995 National Center for Atmospheric Research (NCAR), USA • Professor Jens Oberheide, Hagan develops the first Clemson University, USA • Dr Xiaoli Zhang, version of the global-scale University of Colorado, USA 1997 wave model (GSWM) FUNDING using the 2D model as Current funding for this work is provided by the The pair uses 1D and 2D a blueprint models to estimate upper National Science Foundation (NSF) through Space Weather Program Award ATM-0719480, atmosphere tides generated by NASA Award NNX12AD26G under the by latent heat release in US Participating Investigator (USPI) Program, 2000-02 deep convective clouds and by the National Center for Atmospheric Research which is sponsored by the NSF. Together, Forbes and Hagan adapt Hagan’s CONTACT GSWM for Mars Professor Jeffrey M Forbes observations Project Coordinator 2010-13 Aerospace Engineering Sciences ECOT-634 University of Colorado UCB429 Forbes uses the Challenging Boulder 2008 Minisatellite Payload (CHAMP) and Colorado, 80309 Hagan becomes Gravity Recovery and Climate USA Deputy Director Experiment (GRACE) satellites’ T +1 303 956 4958 of NCAR density measurements to E [email protected] delineate solar and lunar tides 2001-03 in the thermosphere JEFFREY M FORBES (PhD, Harvard, 1975) is Professor of Aerospace Engineering Sciences, The researchers publish University of Colorado at Boulder, and holds the important papers based on Glenn Murphy Endowed Chair. Forbes is a Fellow of the American Geophysical Union (AGU) GSWM-02 findings that link latent and the American Institute of Aeronautics and heat release in deep convective Astronautics (AIAA), and recipient of the AIAA clouds to upper atmosphere Robert M. Losey Atmospheric Sciences Award tides and tidal variability ‘To recognise his extensive contributions to our knowledge and understanding of the re-entry, aerobraking and orbital drag environments of Earth, Mars, and Venus’. MAURA E HAGAN (PhD, Boston College, 1987) is Senior Scientist at the National Center for Atmospheric Research in Boulder, Colorado. Hagan is a Fellow of the American Meteorological Society (AMS), and the American Geophysical Union (AGU) ‘For significant contribution to our understanding of how atmospheric waves determine the state of the atmosphere and ionosphere’.

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