Abstract This article provides an overview of the NASA Atmospheric Tomography (ATom) mission and a summary of selected scientific findings to date. ATom was an airborne measurements and modeling campaign aimed at characterizing the composition and chemistry of the troposphere over the most remote regions of the Pacific, Southern, Atlantic, and Arctic Oceans, and examining the impact of anthropogenic and natural emissions on a global scale. These remote regions dominate global chemical reactivity and are exceptionally important for global air quality and climate. ATom data provide the in situ measurements needed to understand the range of chemical species and their reactions, and to test satellite remote sensing observations and global models over large regions of the remote atmosphere. Lack of data in these regions, particularly over the oceans, has limited our understanding of how atmospheric composition is changing in response to shifting anthropogenic emissions and physical climate change. ATom was designed as a global-scale tomographic sampling mission with extensive geographic and seasonal coverage, tropospheric vertical profiling, and detailed speciation of reactive compounds and pollution tracers. ATom flew the NASA DC-8 research aircraft over four seasons to collect a comprehensive suite of measurements of gases, aerosols, and radical species from the remote troposphere and lower stratosphere on four global circuits from 2016 to 2018. Flights maintained near-continuous vertical profiling of 0.15–13-km altitudes on long meridional transects of the Pacific and Atlantic Ocean basins. Analysis and modeling of ATom data have led to the significant early findings highlighted here.

Atmospheric chemistry

10.1175/bams-d-20-0315.1

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Citations (106)

Cross-Tropopause Mass Exchange and Potential Vorticity Budget in a Simulated Tropopause Folding

Journal of the Atmospheric Sciences (1994)

Jean‐François Lamarque Peter Hess

To study stratosphere–troposphere exchange, an approach based on the nonconservation of potential vorticity (PV) is developed; this approach arises naturally if one defines the tropopause in terms of PV. The evolution of a tropopause fold simulated by a mesoscale model is studied, as well as the evolution of PV at the tropopause level. The PV framework also permits the identification of the physical processes responsible for the cross-tropopause exchange as either diffusive or diabatic. In this model simulation, the diabatic processes are found to be the most important in the exchange. In particular, it is found that the negative heating gradient in the region of the warm sector of the surface cyclone is responsible for most of the diabatic exchange across the tropopause. The mass exchange during the tropopause folding event is estimated to be around 4.9 × 1014 kg in four days over the domain considered (1600 × 2000 km). This number is shown to correspond to the net difference between exchange from stratosphere to troposphere (23.5 × 1014 kg) and exchange from troposphere to stratosphere (18.6 × 1014 kg). Using the results from the exchange of a passive tracer, the exchange of ozone is estimated to be of the order of 1.1 × 108 kg. Finally, the origin of the air exchanged is found to be from the lower stratosphere and the upper troposphere, for the period of four days studied.

Tropopause

Diabatic

Quasi-biennial oscillation

Extratropical cyclone

10.1175/1520-0469(1994)051<2246:ctmeap>2.0.co;2

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Citations (193)

Cloud impacts on photochemistry: a new climatology of photolysis rates from the Atmospheric Tomography mission

Samuel R. Hall Kirk Ullmann Michael J. Prather Clare M. Flynn Lee T. Murray

Abstract. Measurements from actinic flux spectroradiometers on board the NASA DC-8 during the Atmospheric Tomography (ATom) mission provide an extensive set of statistics on how clouds alter photolysis rates (J-values) throughout the remote Pacific and Atlantic Ocean basins. ATom made profiling circumnavigations of the troposphere over four seasons during 2016–2018. J-values are a primary chemical control over tropospheric ozone and methane abundances and their greenhouse effects. Clouds have been recognized for more than three decades as being an important factor in tropospheric chemistry. The ATom climatology of J-values is a unique test of how the chemistry models treat clouds. This work focuses on measurements over the Pacific during the first deployment (ATom-1) in August 2016. Nine global chemistry–climate or –transport models provide J-values for the domains measured in ATom-1. We compare mean profiles over a range of cloudy and clear conditions; but, more importantly, we build a statistical picture of the impact of clouds on J-values through the distribution of the ratio of J-cloudy to J-clear. In detail, the models show largely disparate patterns. When compared with measurements, there is some limited, broad agreement. Models here have resolutions of 50–200 km and thus reduce the occurrence of clear sky when averaging over grid cells. In situ measurements also average the scattered sunlight, but only out to scales of 10 s of km. A primary uncertainty remains in the role of clouds in chemistry, in particular, how models average over cloud fields, and how such averages can simulate measurements.

Atmospheric chemistry

Tropospheric ozone

10.5194/acp-2018-718

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Citations (1)

BrO in the Tropical and Subtropical UTLS: Longitudinal Gradients over the Pacific Ocean

2014 AGU Fall Meeting (2014)

Rainer Volkamer Barbara Dix Sunil Baidar Theodore K. Koenig S. Coburn

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Tropospheric transport differences between models using the same large‐scale meteorological fields

Geophysical Research Letters (2016)

Clara Orbe Darryn W. Waugh Huang Yang Jean‐François Lamarque Simone Tilmes

Abstract The transport of chemicals is a major uncertainty in the modeling of tropospheric composition. A common approach is to transport gases using the winds from meteorological analyses, either using them directly in a chemical transport model or by constraining the flow in a general circulation model. Here we compare the transport of idealized tracers in several different models that use the same meteorological fields taken from Modern‐Era Retrospective analysis for Research and Applications (MERRA). We show that, even though the models use the same meteorological fields, there are substantial differences in their global‐scale tropospheric transport related to large differences in parameterized convection between the simulations. Furthermore, we find that the transport differences between simulations constrained with the same‐large scale flow are larger than differences between free‐running simulations, which have differing large‐scale flow but much more similar convective mass fluxes. Our results indicate that more attention needs to be paid to convective parameterizations in order to understand large‐scale tropospheric transport in models, particularly in simulations constrained with analyzed winds.

10.1002/2016gl071339

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Citations (54)

Supplementary material to "Using airborne observations to improve estimates of short-lived halocarbon emissions during summer from Southern Ocean"

Elizabeth Asher Rebecca S. Hornbrook B. B. Stephens Douglas E. Kinnison Eric J. Morgan

Sea-air exchange calculations 2To support the interpretation of our results, we calculate nominal equilibration times.For 3 estimates of bulk sea-air equilibration times for HVOCs, O 2 , and CO 2 , we assume a mixed layer 4

Halocarbon

10.5194/acp-2019-102-supplement

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Coordination to Understand and Reduce Global Model Biases by U.S. and Chinese Institutions

Bulletin of the American Meteorological Society (2018)

Minghua Zhang Annarita Mariotti Zhaohui Lin V. Ramasmamy Jean‐François Lamarque

© 2018 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).CORRESPONDING AUTHOR: Minghua Zhang, minghua.zhang@stonybrook.eduA supplement to this article is available online (10.1175/BAMS-D-17-0301.2).

Zhàng

10.1175/bams-d-17-0301.1

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Citations (4)

Ozonesonde climatology between 1995 and 2009: description, evaluation and applications

Simone Tilmes Jean‐François Lamarque L. K. Emmons Andrew Conley Martin G. Schultz

Abstract. An ozone climatology based on ozone soundings for the last 15 years has been constructed for model evaluation and comparisons to other observations. Vertical ozone profiles for 41 stations around the globe have been compiled and averaged for the years 1980–1994 and 1995–2009. The climatology provides information about the median and the width of the ozone probability distribution function, as well as interannual variability of ozone between 1995 and 2009, in pressure and tropopause-referenced altitudes. In addition to single stations, regional aggregates are presented, combining stations with similar ozone characteristics. The Hellinger distance is introduced as a new diagnostic to compare the variability of ozone distributions within each region and used for model evaluation purposes. This measure compares not only the mean, but also the shape of distributions. The representativeness of regional aggregates is discussed using independent observations from surface stations and MOZAIC aircraft data. Ozone from all of these data sets show an excellent agreement within the range of the interannual variability, especially if a sufficient number of measurements are available, as is the case for West Europe. Within the climatology, a significant longitudinal variability of ozone in the troposphere and lower stratosphere in the northern mid- and high latitudes is found. The climatology is used to evaluate results from two model intercomparison activities, HTAP for the troposphere and CCMVal2 for the tropopause region and the stratosphere. HTAP ozone is in good agreement with observations in the troposphere within their range of uncertainty, but ozone peaks too early in the Northern Hemisphere spring. The strong gradients of ozone around the tropopause are less well captured by many models. Lower stratospheric ozone is overestimated for all regions by the multi-model mean of CCMVal2 models. Individual models also show major shortcomings in reproducing the shape of ozone probability distribution functions in various regions and different altitudes, which might have significant implications for the radiative budgets in those models.

Tropopause

Tropospheric ozone

10.5194/acpd-11-28747-2011

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Citations (8)