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C. R. Mechoso
,
R. Wood
,
R. Weller
,
C. S. Bretherton
,
A. D. Clarke
,
H. Coe
,
C. Fairall
,
J. T. Farrar
,
G. Feingold
,
R. Garreaud
,
C. Grados
,
J. McWilliams
,
S. P. de Szoeke
,
S. E. Yuter
, and
P. Zuidema

The present paper describes the Variability of the American Monsoon Systems (VAMOS) Ocean–Cloud–Atmosphere–Land Study (VOCALS), an international research program focused on the improved understanding and modeling of the southeastern Pacific (SEP) climate system on diurnal to interannual time scales. In the framework of the SEP climate, VOCALS has two fundamental objectives: 1) improved simulations by coupled atmosphere–ocean general circulation models (CGCMs), with an emphasis on reducing systematic errors in the region; and 2) improved estimates of the indirect effects of aerosols on low clouds and climate, with an emphasis on the more precise quantification of those effects. VOCALS major scientific activities are outlined, and selected achievements are highlighted. Activities described include monitoring in the region, a large international field campaign (the VOCALS Regional Experiment), and two model assessments. The program has already produced significant advances in the understanding of major issues in the SEP: the coastal circulation and the diurnal cycle, the ocean heat budget, factors controlling precipitation and formation of pockets of open cells in stratocumulus decks, aerosol impacts on clouds, and estimation of the first aerosol indirect effect. The paper concludes with a brief presentation on VOCALS contributions to community capacity building before a summary of scientific findings and remaining questions.

Full access
C. R. Wood
,
L. Järvi
,
R. D. Kouznetsov
,
A. Nordbo
,
S. Joffre
,
A. Drebs
,
T. Vihma
,
A. Hirsikko
,
I. Suomi
,
C. Fortelius
,
E. O'Connor
,
D. Moiseev
,
S. Haapanala
,
J. Moilanen
,
M. Kangas
,
A. Karppinen
,
T. Vesala
, and
J. Kukkonen

The Helsinki Urban Boundary-Layer Atmosphere Network (UrBAN: http://urban.fmi.fi) is a dedicated research-grade observational network where the physical processes in the atmosphere above the city are studied. Helsinki UrBAN is the most poleward intensive urban research observation network in the world and thus will allow studying some unique features such as strong seasonality. The network's key purpose is for the understanding of the physical processes in the urban boundary layer and associated fluxes of heat, momentum, moisture, and other gases. A further purpose is to secure a research-grade database, which can be used internationally to validate and develop numerical models of air quality and weather prediction. Scintillometers, a scanning Doppler lidar, ceilometers, a sodar, eddy-covariance stations, and radiometers are used. This equipment is supplemented by auxiliary measurements, which were primarily set up for general weather and/or air-quality mandatory purposes, such as vertical soundings and the operational Doppler radar network. Examples are presented as a testimony to the potential of the network for urban studies, such as (i) evidence of a stable boundary layer possibly coupled to an urban surface, (ii) the comparison of scintillometer data with sonic anemometry above an urban surface, (iii) the application of scanning lidar over a city, and (iv) combination of sodar and lidar to give a fuller range of sampling heights for boundary layer profiling.

Full access
P. W. Thorne
,
R. J. Allan
,
L. Ashcroft
,
P. Brohan
,
R. J. H Dunn
,
M. J. Menne
,
P. R. Pearce
,
J. Picas
,
K. M. Willett
,
M. Benoy
,
S. Bronnimann
,
P. O. Canziani
,
J. Coll
,
R. Crouthamel
,
G. P. Compo
,
D. Cuppett
,
M. Curley
,
C. Duffy
,
I. Gillespie
,
J. Guijarro
,
S. Jourdain
,
E. C. Kent
,
H. Kubota
,
T. P. Legg
,
Q. Li
,
J. Matsumoto
,
C. Murphy
,
N. A. Rayner
,
J. J. Rennie
,
E. Rustemeier
,
L. C. Slivinski
,
V. Slonosky
,
A. Squintu
,
B. Tinz
,
M. A. Valente
,
S. Walsh
,
X. L. Wang
,
N. Westcott
,
K. Wood
,
S. D. Woodruff
, and
S. J. Worley

Abstract

Observations are the foundation for understanding the climate system. Yet, currently available land meteorological data are highly fractured into various global, regional, and national holdings for different variables and time scales, from a variety of sources, and in a mixture of formats. Added to this, many data are still inaccessible for analysis and usage. To meet modern scientific and societal demands as well as emerging needs such as the provision of climate services, it is essential that we improve the management and curation of available land-based meteorological holdings. We need a comprehensive global set of data holdings, of known provenance, that is truly integrated both across essential climate variables (ECVs) and across time scales to meet the broad range of stakeholder needs. These holdings must be easily discoverable, made available in accessible formats, and backed up by multitiered user support. The present paper provides a high-level overview, based upon broad community input, of the steps that are required to bring about this integration. The significant challenge is to find a sustained means to realize this vision. This requires a long-term international program. The database that results will transform our collective ability to provide societally relevant research, analysis, and predictions in many weather- and climate-related application areas across much of the globe.

Open access
R. Paul Lawson
,
Alexei V. Korolev
,
Paul J. DeMott
,
Andrew J. Heymsfield
,
Roelof T. Bruintjes
,
Cory A. Wolff
,
Sarah Woods
,
Ryan J. Patnaude
,
Jørgen B. Jensen
,
Kathryn A. Moore
,
Ivan Heckman
,
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

Free access
Eric J. Jensen
,
Leonhard Pfister
,
David E. Jordan
,
Thaopaul V. Bui
,
Rei Ueyama
,
Hanwant B. Singh
,
Troy D. Thornberry
,
Andrew W. Rollins
,
Ru-Shan Gao
,
David W. Fahey
,
Karen H. Rosenlof
,
James W. Elkins
,
Glenn S. Diskin
,
Joshua P. DiGangi
,
R. Paul Lawson
,
Sarah Woods
,
Elliot L. Atlas
,
Maria A. Navarro Rodriguez
,
Steven C. Wofsy
,
Jasna Pittman
,
Charles G. Bardeen
,
Owen B. Toon
,
Bruce C. Kindel
,
Paul A. Newman
,
Matthew J. McGill
,
Dennis L. Hlavka
,
Leslie R. Lait
,
Mark R. Schoeberl
,
John W. Bergman
,
Henry B. Selkirk
,
M. Joan Alexander
,
Ji-Eun Kim
,
Boon H. Lim
,
Jochen Stutz
, and
Klaus Pfeilsticker

Abstract

The February–March 2014 deployment of the National Aeronautics and Space Administration (NASA) Airborne Tropical Tropopause Experiment (ATTREX) provided unique in situ measurements in the western Pacific tropical tropopause layer (TTL). Six flights were conducted from Guam with the long-range, high-altitude, unmanned Global Hawk aircraft. The ATTREX Global Hawk payload provided measurements of water vapor, meteorological conditions, cloud properties, tracer and chemical radical concentrations, and radiative fluxes. The campaign was partially coincident with the Convective Transport of Active Species in the Tropics (CONTRAST) and the Coordinated Airborne Studies in the Tropics (CAST) airborne campaigns based in Guam using lower-altitude aircraft (see companion articles in this issue). The ATTREX dataset is being used for investigations of TTL cloud, transport, dynamical, and chemical processes, as well as for evaluation and improvement of global-model representations of TTL processes. The ATTREX data are publicly available online (at https://espoarchive.nasa.gov/).

Full access
Stephen Baxter
,
Gerald D Bell
,
Eric S Blake
,
Francis G Bringas
,
Suzana J Camargo
,
Lin Chen
,
Caio A. S Coelho
,
Ricardo Domingues
,
Stanley B Goldenberg
,
Gustavo Goni
,
Nicolas Fauchereau
,
Michael S Halpert
,
Qiong He
,
Philip J Klotzbach
,
John A Knaff
,
Michelle L'Heureux
,
Chris W Landsea
,
I.-I Lin
,
Andrew M Lorrey
,
Jing-Jia Luo
,
Andrew D Magee
,
Richard J Pasch
,
Petra R Pearce
,
Alexandre B Pezza
,
Matthew Rosencrans
,
Blair C Trewin
,
Ryan E Truchelut
,
Bin Wang
,
H Wang
,
Kimberly M Wood
, and
John-Mark Woolley
Free access
Greg M. McFarquhar
,
Christopher S. Bretherton
,
Roger Marchand
,
Alain Protat
,
Paul J. DeMott
,
Simon P. Alexander
,
Greg C. Roberts
,
Cynthia H. Twohy
,
Darin Toohey
,
Steve Siems
,
Yi Huang
,
Robert Wood
,
Robert M. Rauber
,
Sonia Lasher-Trapp
,
Jorgen Jensen
,
Jeffrey L. Stith
,
Jay Mace
,
Junshik Um
,
Emma Järvinen
,
Martin Schnaiter
,
Andrew Gettelman
,
Kevin J. Sanchez
,
Christina S. McCluskey
,
Lynn M. Russell
,
Isabel L. McCoy
,
Rachel L. Atlas
,
Charles G. Bardeen
,
Kathryn A. Moore
,
Thomas C. J. Hill
,
Ruhi S. Humphries
,
Melita D. Keywood
,
Zoran Ristovski
,
Luke Cravigan
,
Robyn Schofield
,
Chris Fairall
,
Marc D. Mallet
,
Sonia M. Kreidenweis
,
Bryan Rainwater
,
John D’Alessandro
,
Yang Wang
,
Wei Wu
,
Georges Saliba
,
Ezra J. T. Levin
,
Saisai Ding
,
Francisco Lang
,
Son C. H. Truong
,
Cory Wolff
,
Julie Haggerty
,
Mike J. Harvey
,
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.

Full access
J. K. Andersen
,
Liss M. Andreassen
,
Emily H. Baker
,
Thomas J. Ballinger
,
Logan T. Berner
,
Germar H. Bernhard
,
Uma S. Bhatt
,
Jarle W. Bjerke
,
Jason E. Box
,
L. Britt
,
R. Brown
,
David Burgess
,
John Cappelen
,
Hanne H. Christiansen
,
B. Decharme
,
C. Derksen
,
D. S. Drozdov
,
Howard E. Epstein
,
L. M. Farquharson
,
Sinead L. Farrell
,
Robert S. Fausto
,
Xavier Fettweis
,
Vitali E. Fioletov
,
Bruce C. Forbes
,
Gerald V. Frost
,
Sebastian Gerland
,
Scott J. Goetz
,
Jens-Uwe Grooß
,
Edward Hanna
,
Inger Hanssen-Bauer
,
Stefan Hendricks
,
Iolanda Ialongo
,
K. Isaksen
,
Bjørn Johnsen
,
L. Kaleschke
,
A. L. Kholodov
,
Seong-Joong Kim
,
Jack Kohler
,
Zachary Labe
,
Carol Ladd
,
Kaisa Lakkala
,
Mark J. Lara
,
Bryant Loomis
,
Bartłomiej Luks
,
K. Luojus
,
Matthew J. Macander
,
G. V. Malkova
,
Kenneth D. Mankoff
,
Gloria L. Manney
,
J. M. Marsh
,
Walt Meier
,
Twila A. Moon
,
Thomas Mote
,
L. Mudryk
,
F. J. Mueter
,
Rolf Müller
,
K. E. Nyland
,
Shad O’Neel
,
James E. Overland
,
Don Perovich
,
Gareth K. Phoenix
,
Martha K. Raynolds
,
C. H. Reijmer
,
Robert Ricker
,
Vladimir E. Romanovsky
,
E. A. G. Schuur
,
Martin Sharp
,
Nikolai I. Shiklomanov
,
C. J. P. P. Smeets
,
Sharon L. Smith
,
Dimitri A. Streletskiy
,
Marco Tedesco
,
Richard L. Thoman
,
J. T. Thorson
,
X. Tian-Kunze
,
Mary-Louise Timmermans
,
Hans Tømmervik
,
Mark Tschudi
,
Dirk van As
,
R. S. W. van de Wal
,
Donald A. Walker
,
John E. Walsh
,
Muyin Wang
,
Melinda Webster
,
Øyvind Winton
,
Gabriel J. Wolken
,
K. Wood
,
Bert Wouters
, and
S. Zador
Free access
Richard L. Thoman
,
Matthew L. Druckenmiller
,
Twila A. Moon
,
L. M. Andreassen
,
E. Baker
,
Thomas J. Ballinger
,
Logan T. Berner
,
Germar H. Bernhard
,
Uma S. Bhatt
,
Jarle W. Bjerke
,
L.N. Boisvert
,
Jason E. Box
,
B. Brettschneider
,
D. Burgess
,
Amy H. Butler
,
John Cappelen
,
Hanne H. Christiansen
,
B. Decharme
,
C. Derksen
,
Dmitry Divine
,
D. S. Drozdov
,
Chereque A. Elias
,
Howard E. Epstein
,
Sinead L. Farrell
,
Robert S. Fausto
,
Xavier Fettweis
,
Vitali E. Fioletov
,
Bruce C. Forbes
,
Gerald V. Frost
,
Sebastian Gerland
,
Scott J. Goetz
,
Jens-Uwe Grooß
,
Christian Haas
,
Edward Hanna
,
-Bauer Inger Hanssen
,
M. M. P. D. Heijmans
,
Stefan Hendricks
,
Iolanda Ialongo
,
K. Isaksen
,
C. D. Jensen
,
Bjørn Johnsen
,
L. Kaleschke
,
A. L. Kholodov
,
Seong-Joong Kim
,
J. Kohler
,
Niels J. Korsgaard
,
Zachary Labe
,
Kaisa Lakkala
,
Mark J. Lara
,
Simon H. Lee
,
Bryant Loomis
,
B. Luks
,
K. Luojus
,
Matthew J. Macander
,
R. Í Magnússon
,
G. V. Malkova
,
Kenneth D. Mankoff
,
Gloria L. Manney
,
Walter N. Meier
,
Thomas Mote
,
Lawrence Mudryk
,
Rolf Müller
,
K. E. Nyland
,
James E. Overland
,
F. Pálsson
,
T. Park
,
C. L. Parker
,
Don Perovich
,
Alek Petty
,
Gareth K. Phoenix
,
J. E. Pinzon
,
Robert Ricker
,
Vladimir E. Romanovsky
,
S. P. Serbin
,
G. Sheffield
,
Nikolai I. Shiklomanov
,
Sharon L. Smith
,
K. M. Stafford
,
A. Steer
,
Dimitri A. Streletskiy
,
Tove Svendby
,
Marco Tedesco
,
L. Thomson
,
T. Thorsteinsson
,
X. Tian-Kunze
,
Mary-Louise Timmermans
,
Hans Tømmervik
,
Mark Tschudi
,
C. J. Tucker
,
Donald A. Walker
,
John E. Walsh
,
Muyin Wang
,
Melinda Webster
,
A. Wehrlé
,
Øyvind Winton
,
G. Wolken
,
K. Wood
,
B. Wouters
, and
D. Yang
Free access
Matthew L. Druckenmiller
,
Twila A. Moon
,
Richard L. Thoman
,
Thomas J. Ballinger
,
Logan T. Berner
,
Germar H. Bernhard
,
Uma S. Bhatt
,
Jarle W. Bjerke
,
Jason E. Box
,
R. Brown
,
John Cappelen
,
Hanne H. Christiansen
,
B. Decharme
,
C. Derksen
,
Dmitry Divine
,
D. S. Drozdov
,
A. Elias Chereque
,
Howard E. Epstein
,
L. M. Farquharson
,
Sinead L. Farrell
,
Robert S. Fausto
,
Xavier Fettweis
,
Vitali E. Fioletov
,
Bruce C. Forbes
,
Gerald V. Frost
,
Emily Gargulinski
,
Sebastian Gerland
,
Scott J. Goetz
,
Z. Grabinski
,
Jens-Uwe Grooß
,
Christian Haas
,
Edward Hanna
,
Inger Hanssen-Bauer
,
Stefan Hendricks
,
Robert M. Holmes
,
Iolanda Ialongo
,
K. Isaksen
,
Piyush Jain
,
Bjørn Johnsen
,
L. Kaleschke
,
A. L. Kholodov
,
Seong-Joong Kim
,
Niels J. Korsgaard
,
Zachary Labe
,
Kaisa Lakkala
,
Mark J. Lara
,
Bryant Loomis
,
K. Luojus
,
Matthew J. Macander
,
G. V. Malkova
,
Kenneth D. Mankoff
,
Gloria L. Manney
,
James W. McClelland
,
Walter N. Meier
,
Thomas Mote
,
L. Mudryk
,
Rolf Müller
,
K. E. Nyland
,
James E. Overland
,
T. Park
,
Olga Pavlova
,
Don Perovich
,
Alek Petty
,
Gareth K. Phoenix
,
Martha K. Raynolds
,
C. H. Reijmer
,
Jacqueline Richter-Menge
,
Robert Ricker
,
Vladimir E. Romanovsky
,
Lindsay Scott
,
Hazel Shapiro
,
Alexander I. Shiklomanov
,
Nikolai I. Shiklomanov
,
C. J. P. P. Smeets
,
Sharon L. Smith
,
Amber Soja
,
Robert G. M. Spencer
,
Sandy Starkweather
,
Dimitri A. Streletskiy
,
Anya Suslova
,
Tove Svendby
,
Suzanne E. Tank
,
Marco Tedesco
,
X. Tian-Kunze
,
Mary-Louise Timmermans
,
Hans Tømmervik
,
Mikhail Tretiakov
,
Mark Tschudi
,
Sofia Vakhutinsky
,
Dirk van As
,
R. S. W. van de Wal
,
Sander Veraverbeke
,
Donald A. Walker
,
John E. Walsh
,
Muyin Wang
,
Melinda Webster
,
Øyvind Winton
,
K. Wood
,
Alison York
, and
Robert Ziel
Free access