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Joseph J-C. Chang
and
Mankin Mak

Abstract

This study investigates the structural properties of the intraseasonal disturbances in the 500-mb flow during a specific winter season (1982/83) and assesses the relevance of normal-mode barotropic instability to the observed intraseasonal disturbances.

The leading complex empirical orthogonal function (CEOF1) accounts for 56% of the variance, has a duration of about 40 days, and mainly comprises the EOF1 and EOF4. It is characterized by a strong planetary-scale fluctuation centered over the eastern Pacific region. Its sign changes at the midseason, arising from an eastward shift of the Pacific trough. The CEOF2 explains 22% of the variance with a period of about 20 days and largely consists of the CEOF2 and EOF3. It depicts a rotating dipole structure over the Atlantic region. The CEOF2 is mainly associated with the pronounced blocking episode in February 1983.

By applying the Gram-Schmidt method in conjunction with an instability analysis, we formulate a dynamical-EOF analysis. The leading DEOF is found to be a barotropically neutral mode that accounts for 34% of the winter-average spatial variance. It bears some resemblance to the EOF1, implying that a large portion of the intraseaonal variability is barotropically neutral with respect to the seasonal-mean flow. By inference, substantial variability is sustained by forcing. The DEOF2 is a slightly modified unstable mode that accounts for 12% of the variance. It partly resembles the blocking. The results suggest that the atmospheric block under consideration is only partly due to the local barotropic instability of the seasonal-mean flow.

A supplementary energetics analysis reveals that the synoptic eddy-forcing mechanism is significant throughout the season, the barotropic instability process occurs intermittently, the dissipation is moderate, and the baroclinic process generally acts against the intraseasonal disturbances. The nonmodal rather the modal form of barotropic instability is probably more important.

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J-C. Joseph Chang
and
Mankin Mak

Abstract

The intraseasonal disturbances and their relation to the corresponding time-mean flows at 500 mb of nine boreal winters me investigated. The barotropic normal mode instability properties of the seasonal mean flow are found not to be indicative of the intensity of the intraseasonal variability. An application of the dynamical empirical orthogonal function (DEOF) analysis to two distinctly different seasons reveals that only a small fraction of the observed intraseasonal variance is identifiable with the unstable normal modes as individual entities. Each of the few leading DEOFs mainly consists of a slightly modified stable normal mode.

The nonmodal growth of the observed intraseasonal disturbances is analyzed in the context of optimal modes with respect to the corresponding seasonal mean flows for different optimization times. The amplifying 1-day optimal structures are much more in number and have much greater growth rate than the unstable normal modes. Several narrow bands of such optimal modes are particularly prevalent. The most pronounced band has a characteristic time of about 20 days and has a localized structure over the Atlantic. The daily variation of the kinetic energy associated with all the 1-day amplifying optimal structures supports the notion that the nonmodal growth is important for the intraseasonal disturbances in winter. The evolution of all the amplifying optimal modes for a longer optimization time such as τ = 4 days over a period of τ does not describe the variation of the observed disturbances nearly as well.

The synoptic-scale eddy forcing of the intraseasonal disturbances contributes significantly to the intraseasonal variability in the winter hemisphere.

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Steven R. Hanna
and
Joseph C. Chang

Abstract

The field program phase of the Lake Michigan Ozone Study (LMOS) took place during the summer of 1991. Observed ozone concentrations and weather variables have been analyzed for the Lake Michigan region and the eastern United States for four 1991 LMOS ozone episodes covering 21 days. It is found that all LMOS episodes are associated with large polluted regions with dimensions of 1000–2000 km, located on the western side of high pressure systems centered over the eastern United States. Consequently, the air coming into the LMOS region contains significant amounts of ozone, haze, and other pollutants advected along trajectories with anticyclonic curvature originating in upwind source regions from St. Louis, through the Ohio River valley, and into the northeast megalopolis. The local sources in the Gary-Chicago-Milwaukee region then add to this already polluted air mass, where concentrations are influenced by the strong stability of the boundary layer over Lake Michigan and the associated lake-land-breeze circulations. However, the magnitudes of ozone concentrations in the LMOS region are often quickly and significantly reduced by rain and by fronts, which are present in some portion of the domain during nearly all of the days that were studied. The portion of the urban ozone plume that is not influenced by rain and fronts is observed to be advected into rural areas at downwind distances of 100–200 km or more from Chicago, and often has concentrations higher than those in Chicago. Whether maximum concentrations are located on the western or the eastern shoreline of Lake Michigan depends on whether winds have an easterly or westerly component.

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Joseph C. Chang
,
Pasquale Franzese
,
Kittisak Chayantrakom
, and
Steven R. Hanna

Abstract

Results of evaluations of transport and dispersion models with field data are summarized. The California Puff (CALPUFF), Hazard Prediction and Assessment Capability (HPAC), and Chemical/Biological Agent Vapor, Liquid, and Solid Tracking (VLSTRACK) models were compared using two recent mesoscale field datasets—the Dipole Pride 26 (DP26) and the Overland Along-wind Dispersion (OLAD). Both field experiments involved instantaneous releases of sulfur hexafluoride tracer gas in a mesoscale region with desert basins and mountains. DP26 involved point sources, and OLAD involved line sources. Networks of surface wind observations and special radiosonde and pilot balloon soundings were available, and tracer concentrations were observed along lines of whole-air samplers and some fast-response instruments at distances up to 20 km. The models were evaluated using the maximum 3-h dosage (concentration integrated over time) along a sampling line. It was found that the solutions were highly dependent upon the diagnostic wind field model used to interpolate the spatially variable observed wind fields. At the DP26 site, CALPUFF and HPAC had better performance than VLSTRACK. Overall, the three models had mean biases within 35% and random scatters of about a factor of 3–4. About 50%–60% of CALPUFF and HPAC predictions and about 40% of VLSTRACK predictions were within a factor of 2 of observations. At the OLAD site, all three models underpredicted by a factor of 2–3, on average, with random scatters of a factor of 3–7. About 50% of HPAC predictions and only 25%–30% of CALPUFF and VLSTRACK predictions were within a factor of 2 of observations.

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Joseph C. Chang
,
Steven R. Hanna
,
Zafer Boybeyi
, and
Pasquale Franzese

Abstract

After the terrorist incidents on 11 September 2001, there is a greatly heightened concern about the potential impacts of acts of terrorism involving the atmospheric release of chemical, biological, radiological, and nuclear (CBRN) materials in urban areas. In response to the need for an urban CBRN model, the Urban Hazard Prediction Assessment Capability (Urban HPAC) transport and dispersion model has been developed. Because HPAC is widely used by the Department of Defense community for planning, training, and operational and tactical purposes, it is of great importance that the new model be adequately evaluated with urban datasets to demonstrate its accuracy. This paper describes evaluations of Urban HPAC using the “URBAN 2000” urban tracer and meteorological field experiment data from Salt Lake City, Utah. Four Urban HPAC model configuration options and five plausible meteorological input data options—ranging from data-sparse to data-rich scenarios—were considered in the study, thus leading to a total of 20 possible model combinations. For the maximum concentrations along each sampling arc for each intensive operating period (IOP), the 20 Urban HPAC model combinations gave consistent mean overpredictions of about 50%, with a range over the 20 model combinations from no overprediction to a factor-of-4 overprediction in the mean. The median of the random scatter for the 20 model combinations was about a factor of 3 of the mean, with a range over the 20 model combinations between a factor of about 2 and 9. These performance measures satisfy previously established acceptance criteria for dispersion models.

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Ian M. Brooks
,
Margaret J. Yelland
,
Robert C. Upstill-Goddard
,
Philip D. Nightingale
,
Steve Archer
,
Eric d'Asaro
,
Rachael Beale
,
Cory Beatty
,
Byron Blomquist
,
A. Anthony Bloom
,
Barbara J. Brooks
,
John Cluderay
,
David Coles
,
John Dacey
,
Michael DeGrandpre
,
Jo Dixon
,
William M. Drennan
,
Joseph Gabriele
,
Laura Goldson
,
Nick Hardman-Mountford
,
Martin K. Hill
,
Matt Horn
,
Ping-Chang Hsueh
,
Barry Huebert
,
Gerrit de Leeuw
,
Timothy G. Leighton
,
Malcolm Liddicoat
,
Justin J. N. Lingard
,
Craig McNeil
,
James B. McQuaid
,
Ben I. Moat
,
Gerald Moore
,
Craig Neill
,
Sarah J. Norris
,
Simon O'Doherty
,
Robin W. Pascal
,
John Prytherch
,
Mike Rebozo
,
Erik Sahlee
,
Matt Salter
,
Ute Schuster
,
Ingunn Skjelvan
,
Hans Slagter
,
Michael H. Smith
,
Paul D. Smith
,
Meric Srokosz
,
John A. Stephens
,
Peter K. Taylor
,
Maciej Telszewski
,
Roisin Walsh
,
Brian Ward
,
David K. Woolf
,
Dickon Young
, and
Henk Zemmelink

As part of the U.K. contribution to the international Surface Ocean-Lower Atmosphere Study, a series of three related projects—DOGEE, SEASAW, and HiWASE—undertook experimental studies of the processes controlling the physical exchange of gases and sea spray aerosol at the sea surface. The studies share a common goal: to reduce the high degree of uncertainty in current parameterization schemes. The wide variety of measurements made during the studies, which incorporated tracer and surfactant release experiments, included direct eddy correlation fluxes, detailed wave spectra, wind history, photographic retrievals of whitecap fraction, aerosolsize spectra and composition, surfactant concentration, and bubble populations in the ocean mixed layer. Measurements were made during three cruises in the northeast Atlantic on the RRS Discovery during 2006 and 2007; a fourth campaign has been making continuous measurements on the Norwegian weather ship Polarfront since September 2006. This paper provides an overview of the three projects and some of the highlights of the measurement campaigns.

Full access
Ian M. Brooks
,
Margaret J. Yelland
,
Robert C. Upstill-Goddard
,
Philip D. Nightingale
,
Steve Archer
,
Eric d'Asaro
,
Rachael Beale
,
Cory Beatty
,
Byron Blomquist
,
A. Anthony Bloom
,
Barbara J. Brooks
,
John Cluderay
,
David Coles
,
John Dacey
,
Michael Degrandpre
,
Jo Dixon
,
William M. Drennan
,
Joseph Gabriele
,
Laura Goldson
,
Nick Hardman-Mountford
,
Martin K. Hill
,
Matt Horn
,
Ping-Chang Hsueh
,
Barry Huebert
,
Gerrit De Leeuw
,
Timothy G. Leighton
,
Malcolm Liddicoat
,
Justin J. N. Lingard
,
Craig Mcneil
,
James B. Mcquaid
,
Ben I. Moat
,
Gerald Moore
,
Craig Neill
,
Sarah J. Norris
,
Simon O'Doherty
,
Robin W. Pascal
,
John Prytherch
,
Mike Rebozo
,
Erik Sahlee
,
Matt Salter
,
Ute Schuster
,
Ingunn Skjelvan
,
Hans Slagter
,
Michael H. Smith
,
Paul D. Smith
,
Meric Srokosz
,
John A. Stephens
,
Peter K. Taylor
,
Maciej Telszewski
,
Roisin Walsh
,
Brian Ward
,
David K. Woolf
,
Dickon Young
, and
Henk Zemmelink

Abstract

No Abstract available.

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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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Peter Bissolli
,
Catherine Ganter
,
Tim Li
,
Ademe Mekonnen
,
Ahira Sánchez-Lugo
,
Eric J. Alfaro
,
Lincoln M. Alves
,
Jorge A. Amador
,
B. Andrade
,
Francisco Argeñalso
,
P. Asgarzadeh
,
Julian Baez
,
Reuben Barakiza
,
M. Yu. Bardin
,
Mikhail Bardin
,
Oliver Bochníček
,
Brandon Bukunt
,
Blanca Calderón
,
Jayaka D. Campbell
,
Elise Chandler
,
Ladislaus Chang’a
,
Vincent Y. S. Cheng
,
Leonardo A. Clarke
,
Kris Correa
,
Catalina Cortés
,
Felipe Costa
,
A.P.M.A. Cunha
,
Mesut Demircan
,
K. R. Dhurmea
,
A. Diawara
,
Sarah Diouf
,
Dashkhuu Dulamsuren
,
M. ElKharrim
,
Jhan-Carlo Espinoza
,
A. Fazl-Kazem
,
Chris Fenimore
,
Steven Fuhrman
,
Karin Gleason
,
Charles “Chip” P. Guard
,
Samson Hagos
,
Mizuki Hanafusa
,
H. R. Hasannezhad
,
Richard R. Heim Jr.
,
Hugo G. Hidalgo
,
J. A. Ijampy
,
Gyo Soon Im
,
Annie C. Joseph
,
G. Jumaux
,
K. R. Kabidi
,
P-H. Kamsu-Tamo
,
John Kennedy
,
Valentina Khan
,
Mai Van Khiem
,
Philemon King’uza
,
Natalia N. Korshunova
,
A. C. Kruger
,
Hoang Phuc Lam
,
Mark A. Lander
,
Waldo Lavado-Casimiro
,
Tsz-Cheung Lee
,
Kinson H. Y. Leung
,
Gregor Macara
,
Jostein Mamen
,
José A. Marengo
,
Charlotte McBride
,
Noelia Misevicius
,
Aurel Moise
,
Jorge Molina-Carpio
,
Natali Mora
,
Awatif E. Mostafa
,
Habiba Mtongori
,
Charles Mutai
,
O. Ndiaye
,
Juan José Nieto
,
Latifa Nyembo
,
Patricia Nying’uro
,
Xiao Pan
,
Reynaldo Pascual Ramírez
,
David Phillips
,
Brad Pugh
,
Madhavan Rajeevan
,
M. L. Rakotonirina
,
Andrea M. Ramos
,
M. Robjhon
,
Camino Rodriguez
,
Guisado Rodriguez
,
Josyane Ronchail
,
Benjamin Rösner
,
Roberto Salinas
,
Hirotaka Sato
,
Hitoshi Sato
,
Amal Sayouri
,
Joseph Sebaziga
,
Serhat Sensoy
,
Sandra Spillane
,
Katja Trachte
,
Gerard van der Schrier
,
F. Sima
,
Adam Smith
,
Jacqueline M. Spence
,
O. P. Sreejith
,
A. K. Srivastava
,
José L. Stella
,
Kimberly A. Stephenson
,
Tannecia S. Stephenson
,
S. Supari
,
Sahar Tajbakhsh-Mosalman
,
Gerard Tamar
,
Michael A. Taylor
,
Asaminew Teshome
,
Wassila M. Thiaw
,
Skie Tobin
,
Adrian R. Trotman
,
Cedric J. Van Meerbeeck
,
A. Vazifeh
,
Shunya Wakamatsu
,
Wei Wang
,
Fei Xin
,
F. Zeng
,
Peiqun Zhang
, and
Zhiwei Zhu
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