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Christina S. McCluskey
,
Thomas C. J. Hill
,
Camille M. Sultana
,
Olga Laskina
,
Jonathan Trueblood
,
Mitchell V. Santander
,
Charlotte M. Beall
,
Jennifer M. Michaud
,
Sonia M. Kreidenweis
,
Kimberly A. Prather
,
Vicki Grassian
, and
Paul J. DeMott

Abstract

The abundance of atmospheric ice nucleating particles (INPs) is a source of uncertainty for numerical representation of ice-phase transitions in mixed-phase clouds. While sea spray aerosol (SSA) exhibits less ice nucleating (IN) ability than terrestrial aerosol, marine INP emissions are linked to oceanic biological activity and are potentially an important source of INPs over remote oceans. Inadequate knowledge of marine INP identity limits the ability to parameterize this complex INP source. A previous manuscript described abundances of marine INPs in relation to several aerosol composition and ocean biology observations during two laboratory mesocosm experiments. In this study, the abundances and chemical and physical properties of INPs found during the same mesocosm experiments were directly probed in SSA, seawater, and surface microlayer samples. Two unique marine INP populations were found: 1) dissolved organic carbon INPs are suggested to be composed of IN-active molecules, and 2) particulate organic carbon INPs are attributed as intact cells or IN-active microbe fragments. Both marine INP types are likely to be emitted into SSA following decay of phytoplankton biomass when 1) the surface microlayer is significantly enriched with exudates and cellular detritus and SSA particles are preferentially coated with IN-active molecules or 2) diatom fragments and bacteria are relatively abundant in seawater and therefore more likely transferred into SSA. These findings inform future efforts for incorporating marine INP emissions into numerical models and motivate future studies to quantify specific marine molecules and isolate phytoplankton, bacteria, and other species that contribute to these marine INP types.

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R. Paul Lawson
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Alexei V. Korolev
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Paul J. DeMott
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Andrew J. Heymsfield
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Roelof T. Bruintjes
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Cory A. Wolff
,
Sarah Woods
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Ryan J. Patnaude
,
Jørgen B. Jensen
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Kathryn A. Moore
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Ivan Heckman
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Elise Rosky
,
Julie Haggerty
,
Russell J. Perkins
,
Ted Fisher
, and
Thomas C. J. Hill

Abstract

The secondary ice process (SIP) is a major microphysical process, which can result in rapid enhancement of ice particle concentration in the presence of preexisting ice. SPICULE was conducted to further investigate the effect of collision–coalescence on the rate of the fragmentation of freezing drop (FFD) SIP mechanism in cumulus congestus clouds. Measurements were conducted over the Great Plains and central United States from two coordinated aircraft, the NSF Gulfstream V (GV) and SPEC Learjet 35A, both equipped with state-of-the-art microphysical instrumentation and vertically pointing W- and Ka-band radars, respectively. The GV primarily targeted measurements of subcloud aerosols with subsequent sampling in warm cloud. Simultaneously, the Learjet performed multiple penetrations of the ascending cumulus congestus (CuCg) cloud top. First primary ice was typically detected at temperatures colder than −10°C, consistent with measured ice nucleating particles. Subsequent production of ice via FFD SIP was strongly related to the concentration of supercooled large drops (SLDs), with diameters from about 0.2 to a few millimeters. The concentration of SLDs is directly linked to the rate of collision–coalescence, which depends primarily on the subcloud aerosol size distribution and cloud-base temperature. SPICULE supports previous observational results showing that FFD SIP efficiency could be deduced from the product of cloud-base temperature and maximum diameter of drops measured ∼300 m above cloud base. However, new measurements with higher concentrations of aerosol and total cloud-base drop concentrations show an attenuating effect on the rate of coalescence. The SPICULE dataset provides rich material for validation of numerical schemes of collision–coalescence and SIP to improve weather prediction simulations

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Christina S. McCluskey
,
Thomas C. J. Hill
,
Francesca Malfatti
,
Camille M. Sultana
,
Christopher Lee
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Mitchell V. Santander
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Charlotte M. Beall
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Kathryn A. Moore
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Gavin C. Cornwell
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Douglas B. Collins
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Kimberly A. Prather
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Thilina Jayarathne
,
Elizabeth A. Stone
,
Farooq Azam
,
Sonia M. Kreidenweis
, and
Paul J. DeMott

Abstract

Emission rates and properties of ice nucleating particles (INPs) are required for proper representation of aerosol–cloud interactions in atmospheric models. Few investigations have quantified marine INP emissions, a potentially important INP source for remote oceanic regions. Previous studies have suggested INPs in sea spray aerosol (SSA) are linked to oceanic biological activity. This proposed link was explored in this study by measuring INP emissions from nascent SSA during phytoplankton blooms during two mesocosm experiments. In a Marine Aerosol Reference Tank (MART) experiment, a phytoplankton bloom was produced with chlorophyll-a (Chl a) concentrations reaching 39 μg L−1, while Chl a concentrations more representative of natural ocean conditions were obtained during the Investigation into Marine Particle Chemistry and Transfer Science (IMPACTS; peak Chl a of 5 μg L−1) campaign, conducted in the University of California, San Diego, wave flume. Dynamic trends in INP emissions occurred for INPs active at temperatures > −30°C. Increases in INPs active between −25° and −15°C lagged the peak in Chl a in both studies, suggesting a consistent population of INPs associated with the collapse of phytoplankton blooms. Trends in INP emissions were also compared to aerosol composition, abundances of microbes, and enzyme activity. In general, increases in INP concentrations corresponded to increases in organic species in SSA and the emissions of heterotrophic bacteria, suggesting that both microbes and biomolecules contribute to marine INP populations. INP trends were not directly correlated with a single biological marker in either study. Direct measurements of INP chemistry are needed to accurately identify particles types contributing to marine INP populations.

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Adam C. Varble
,
Stephen W. Nesbitt
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Paola Salio
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Joseph C. Hardin
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Nitin Bharadwaj
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Paloma Borque
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Paul J. DeMott
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Zhe Feng
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Thomas C. J. Hill
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James N. Marquis
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Alyssa Matthews
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Fan Mei
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Rusen Öktem
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Vagner Castro
,
Lexie Goldberger
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Alexis Hunzinger
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Kevin R. Barry
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Sonia M. Kreidenweis
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Greg M. McFarquhar
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Lynn A. McMurdie
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Mikhail Pekour
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Heath Powers
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David M. Romps
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Celeste Saulo
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Beat Schmid
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Jason M. Tomlinson
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Susan C. van den Heever
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Alla Zelenyuk
,
Zhixiao Zhang
, and
Edward J. Zipser

Abstract

The Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was designed to improve understanding of orographic cloud life cycles in relation to surrounding atmospheric thermodynamic, flow, and aerosol conditions. The deployment to the Sierras de Córdoba range in north-central Argentina was chosen because of very frequent cumulus congestus, deep convection initiation, and mesoscale convective organization uniquely observable from a fixed site. The C-band Scanning Atmospheric Radiation Measurement (ARM) Precipitation Radar was deployed for the first time with over 50 ARM Mobile Facility atmospheric state, surface, aerosol, radiation, cloud, and precipitation instruments between October 2018 and April 2019. An intensive observing period (IOP) coincident with the RELAMPAGO field campaign was held between 1 November and 15 December during which 22 flights were performed by the ARM Gulfstream-1 aircraft. A multitude of atmospheric processes and cloud conditions were observed over the 7-month campaign, including numerous orographic cumulus and stratocumulus events; new particle formation and growth producing high aerosol concentrations; drizzle formation in fog and shallow liquid clouds; very low aerosol conditions following wet deposition in heavy rainfall; initiation of ice in congestus clouds across a range of temperatures; extreme deep convection reaching 21-km altitudes; and organization of intense, hail-containing supercells and mesoscale convective systems. These comprehensive datasets include many of the first ever collected in this region and provide new opportunities to study orographic cloud evolution and interactions with meteorological conditions, aerosols, surface conditions, and radiation in mountainous terrain.

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Bart Geerts
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Scott E. Giangrande
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Greg M. McFarquhar
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Lulin Xue
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Steven J. Abel
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Jennifer M. Comstock
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Susanne Crewell
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Paul J. DeMott
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Kerstin Ebell
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Paul Field
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Thomas C. J. Hill
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Alexis Hunzinger
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Michael P. Jensen
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Karen L. Johnson
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Timothy W. Juliano
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Pavlos Kollias
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Branko Kosovic
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Christian Lackner
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Ed Luke
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Christof Lüpkes
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Alyssa A. Matthews
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Roel Neggers
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Mikhail Ovchinnikov
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Heath Powers
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Matthew D. Shupe
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Thomas Spengler
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Benjamin E. Swanson
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Michael Tjernström
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Adam K. Theisen
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Nathan A. Wales
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Yonggang Wang
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Manfred Wendisch
, and
Peng Wu

Abstract

One of the most intense air mass transformations on Earth happens when cold air flows from frozen surfaces to much warmer open water in cold-air outbreaks (CAOs), a process captured beautifully in satellite imagery. Despite the ubiquity of the CAO cloud regime over high-latitude oceans, we have a rather poor understanding of its properties, its role in energy and water cycles, and its treatment in weather and climate models. The Cold-Air Outbreaks in the Marine Boundary Layer Experiment (COMBLE) was conducted to better understand this regime and its representation in models. COMBLE aimed to examine the relations between surface fluxes, boundary layer structure, aerosol, cloud, and precipitation properties, and mesoscale circulations in marine CAOs. Processes affecting these properties largely fall in a range of scales where boundary layer processes, convection, and precipitation are tightly coupled, which makes accurate representation of the CAO cloud regime in numerical weather prediction and global climate models most challenging. COMBLE deployed an Atmospheric Radiation Measurement Mobile Facility at a coastal site in northern Scandinavia (69°N), with additional instruments on Bear Island (75°N), from December 2019 to May 2020. CAO conditions were experienced 19% (21%) of the time at the main site (on Bear Island). A comprehensive suite of continuous in situ and remote sensing observations of atmospheric conditions, clouds, precipitation, and aerosol were collected. Because of the clouds’ well-defined origin, their shallow depth, and the broad range of observed temperature and aerosol concentrations, the COMBLE dataset provides a powerful modeling testbed for improving the representation of mixed-phase cloud processes in large-eddy simulations and large-scale models.

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Greg M. McFarquhar
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Christopher S. Bretherton
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Roger Marchand
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Alain Protat
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Paul J. DeMott
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Simon P. Alexander
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Greg C. Roberts
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Cynthia H. Twohy
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Darin Toohey
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Steve Siems
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Yi Huang
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Robert Wood
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Robert M. Rauber
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Sonia Lasher-Trapp
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Jorgen Jensen
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Jeffrey L. Stith
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Jay Mace
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Junshik Um
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Emma Järvinen
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Martin Schnaiter
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Andrew Gettelman
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Kevin J. Sanchez
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Christina S. McCluskey
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Lynn M. Russell
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Isabel L. McCoy
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Rachel L. Atlas
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Charles G. Bardeen
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Kathryn A. Moore
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Thomas C. J. Hill
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Ruhi S. Humphries
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Melita D. Keywood
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Zoran Ristovski
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Luke Cravigan
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Robyn Schofield
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Chris Fairall
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Marc D. Mallet
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Sonia M. Kreidenweis
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Bryan Rainwater
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John D’Alessandro
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Yang Wang
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Wei Wu
,
Georges Saliba
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Ezra J. T. Levin
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Saisai Ding
,
Francisco Lang
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Son C. H. Truong
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Cory Wolff
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Julie Haggerty
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Mike J. Harvey
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Andrew R. Klekociuk
, and
Adrian McDonald

Abstract

Weather and climate models are challenged by uncertainties and biases in simulating Southern Ocean (SO) radiative fluxes that trace to a poor understanding of cloud, aerosol, precipitation, and radiative processes, and their interactions. Projects between 2016 and 2018 used in situ probes, radar, lidar, and other instruments to make comprehensive measurements of thermodynamics, surface radiation, cloud, precipitation, aerosol, cloud condensation nuclei (CCN), and ice nucleating particles over the SO cold waters, and in ubiquitous liquid and mixed-phase clouds common to this pristine environment. Data including soundings were collected from the NSF–NCAR G-V aircraft flying north–south gradients south of Tasmania, at Macquarie Island, and on the R/V Investigator and RSV Aurora Australis. Synergistically these data characterize boundary layer and free troposphere environmental properties, and represent the most comprehensive data of this type available south of the oceanic polar front, in the cold sector of SO cyclones, and across seasons. Results show largely pristine environments with numerous small and few large aerosols above cloud, suggesting new particle formation and limited long-range transport from continents, high variability in CCN and cloud droplet concentrations, and ubiquitous supercooled water in thin, multilayered clouds, often with small-scale generating cells near cloud top. These observations demonstrate how cloud properties depend on aerosols while highlighting the importance of dynamics and turbulence that likely drive heterogeneity of cloud phase. Satellite retrievals confirmed low clouds were responsible for radiation biases. The combination of models and observations is examining how aerosols and meteorology couple to control SO water and energy budgets.

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Chelsea R. Thompson
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Steven C. Wofsy
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Michael J. Prather
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Paul A. Newman
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Thomas F. Hanisco
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Thomas B. Ryerson
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David W. Fahey
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Eric C. Apel
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Charles A. Brock
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William H. Brune
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Karl Froyd
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Joseph M. Katich
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Julie M. Nicely
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Jeff Peischl
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Eric Ray
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Patrick R. Veres
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Siyuan Wang
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Hannah M. Allen
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Elizabeth Asher
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Huisheng Bian
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Donald Blake
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Ilann Bourgeois
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John Budney
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T. Paul Bui
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Amy Butler
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Pedro Campuzano-Jost
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Cecilia Chang
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Mian Chin
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Róisín Commane
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Gus Correa
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John D. Crounse
,
Bruce Daube
,
Jack E. Dibb
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Joshua P. DiGangi
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Glenn S. Diskin
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Maximilian Dollner
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James W. Elkins
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Arlene M. Fiore
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Clare M. Flynn
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Hao Guo
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Samuel R. Hall
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Reem A. Hannun
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Alan Hills
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Eric J. Hintsa
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Alma Hodzic
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Rebecca S. Hornbrook
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L. Greg Huey
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Jose L. Jimenez
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Ralph F. Keeling
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Michelle J. Kim
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Agnieszka Kupc
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Forrest Lacey
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Leslie R. Lait
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Jean-Francois Lamarque
,
Junhua Liu
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Kathryn McKain
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Simone Meinardi
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David O. Miller
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Stephen A. Montzka
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Fred L. Moore
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Eric J. Morgan
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Daniel M. Murphy
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Lee T. Murray
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Benjamin A. Nault
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J. Andrew Neuman
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Louis Nguyen
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Yenny Gonzalez
,
Andrew Rollins
,
Karen Rosenlof
,
Maryann Sargent
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Gregory Schill
,
Joshua P. Schwarz
,
Jason M. St. Clair
,
Stephen D. Steenrod
,
Britton B. Stephens
,
Susan E. Strahan
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Sarah A. Strode
,
Colm Sweeney
,
Alexander B. Thames
,
Kirk Ullmann
,
Nicholas Wagner
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Rodney Weber
,
Bernadett Weinzierl
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Paul O. Wennberg
,
Christina J. Williamson
,
Glenn M. Wolfe
, and
Linghan Zeng

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.

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