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G. Alexander Sokolowsky
,
Sean W. Freeman
, and
Susan C. van den Heever

Abstract

A trimodal convective cloud distribution is commonly observed within the tropics due to the tropical-mean thermodynamic environment. The goal of this research has been to examine the integrated impacts of thermodynamic and aerosol properties on both the convective environment and the properties of the cloud modes themselves. This has been achieved by using LES experiments in which various thermodynamic and aerosol environments were independently and simultaneously perturbed. The key conclusions from this study are 1) large amounts of aerosol loading and low-level static stability suppress the bulk environment and the intensity and coverage of convective clouds; 2) cloud and environmental responses to aerosol loading tend to be stronger than those from static stability; 3) the effects of aerosol and stability perturbations modulate each other substantially; 4) the deepest convection and highest dynamical intensity occur at moderate aerosol loading, rather than at low or high loading; and 5) most of the strongest feedbacks due to aerosol and stability perturbations are seen in the boundary layer, though some are stronger above the freezing level. These results underscore the importance of considering the thermodynamic environment’s impact on aerosol-induced convective invigoration while highlighting the dominance of aerosol impacts on the trimodal distribution and revealing synergies between thermodynamics and aerosols.

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Aaron R. Naeger
,
Michael J. Newchurch
,
Tom Moore
,
Kelly Chance
,
Xiong Liu
,
Susan Alexander
,
Kelley Murphy
, and
Bo Wang
Full access
Alexander Sen Gupta
,
Les C. Muir
,
Jaclyn N. Brown
,
Steven J. Phipps
,
Paul J. Durack
,
Didier Monselesan
, and
Susan E. Wijffels

Abstract

Even in the absence of external forcing, climate models often exhibit long-term trends that cannot be attributed to natural variability. This so-called climate drift arises for various reasons including the following: perturbations to the climate system on coupling component models together and deficiencies in model physics and numerics. When examining trends in historical or future climate simulations, it is important to know the error introduced by drift so that action can be taken where necessary. This study assesses the importance of drift for a number of climate properties at global and local scales. To illustrate this, the present paper focuses on simulated trends over the second half of the twentieth century. While drift in globally averaged surface properties is generally considerably smaller than observed and simulated twentieth-century trends, it can still introduce nontrivial errors in some models. Furthermore, errors become increasingly important at smaller scales. The direction of drift is not systematic across different models or variables, as such drift is considerably reduced in the multimodel mean. Despite drift being primarily associated with ocean adjustment, it is also apparent in atmospheric variables. For example, most models have local drift magnitudes in surface air and ocean temperatures that are typically between 15% and 35% of the twentieth-century simulation trend magnitudes for 1950–2000. Below depths of 1000–2000 m, drift dominates over any forced trend in most regions. As such steric sea level is strongly affected and for some models and regions the sea level trend direction is reversed. Thus depending on the application, drift may be negligible or may make up an important part of the simulated trend.

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Aaron R. Naeger
,
Michael J. Newchurch
,
Tom Moore
,
Kelly Chance
,
Xiong Liu
,
Susan Alexander
,
Kelley Murphy
, and
Bo Wang
Full access
Pavel Ya. Groisman
,
Elizabeth A. Clark
,
Vladimir M. Kattsov
,
Dennis P. Lettenmaier
,
Irina N. Sokolik
,
Vladimir B. Aizen
,
Oliver Cartus
,
Jiquan Chen
,
Susan Conard
,
John Katzenberger
,
Olga Krankina
,
Jaakko Kukkonen
,
Toshinobu Machida
,
Shamil Maksyutov
,
Dennis Ojima
,
Jiaguo Qi
,
Vladimir E. Romanovsky
,
Maurizio Santoro
,
Christiane C. Schmullius
,
Alexander I. Shiklomanov
,
Kou Shimoyama
,
Herman H. Shugart
,
Jacquelyn K. Shuman
,
Mikhail A. Sofiev
,
Anatoly I. Sukhinin
,
Charles Vörösmarty
,
Donald Walker
, and
Eric F. Wood

Northern Eurasia, the largest landmass in the northern extratropics, accounts for ~20% of the global land area. However, little is known about how the biogeochemical cycles, energy and water cycles, and human activities specific to this carbon-rich, cold region interact with global climate. A major concern is that changes in the distribution of land-based life, as well as its interactions with the environment, may lead to a self-reinforcing cycle of accelerated regional and global warming. With this as its motivation, the Northern Eurasian Earth Science Partnership Initiative (NEESPI) was formed in 2004 to better understand and quantify feedbacks between northern Eurasian and global climates. The first group of NEESPI projects has mostly focused on assembling regional databases, organizing improved environmental monitoring of the region, and studying individual environmental processes. That was a starting point to addressing emerging challenges in the region related to rapidly and simultaneously changing climate, environmental, and societal systems. More recently, the NEESPI research focus has been moving toward integrative studies, including the development of modeling capabilities to project the future state of climate, environment, and societies in the NEESPI domain. This effort will require a high level of integration of observation programs, process studies, and modeling across disciplines.

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