Report on CCSM Climate Variability Working Group Meeting

Seventh Annual CCSM Workshop, The Village at Breckenridge

Co-Chairs: Jim Hurrell and Michael Alexander

25 June 2002

The CCSM Climate Variability Working Group (CVWG) breakout session was held on Tuesday, June 25, 2002 from 11:00 am to 3:30 pm. Jim Hurrell chaired the session and Mike Alexander served as rapporteur. Prior to the meeting, talks had been solicited from members of the CCSM community to document aspects of the climate and variability of the new CCSM 2.0 control simulation. The individual presentations are summarized below. They are also available over the web: http://www.cgd.ucar.edu/~jhurrell/cvwg.html.

A subjective assessment of variability in the CCSM2 Control simulation:

Jim Hurrell (NCAR): Atmospheric mean state and seasonal cycle
Jim examined the annual mean and seasonal cycle of SST, precipitation, velocity potential, zonal wind, SLP and eddy stream function. Like most CGCMs the cold tongue is too cold and extends too far west. There is a double ITCZ. Extratropical eddies are fairly well simulated.

R. Saravanan (NCAR): Extratropical patterns of atmospheric variability
Spatial patterns and amplitudes of the simulated NAO and PNA variability in CCSM2 are comparable to observations, and somewhat better than in CSM1. Normalized trends in SST are much stronger than trends in the atmospheric variables. The atmospheric trend resembles the atmospheric response to a prescribed SST anomaly.

Michael Alexander (CDC): Upper ocean climate and variability
Mike examined the mean net surface heat flux, mixed layer depth, sea surface salinity, and surface currents, and variability of SST and thermocline depth (z20). Examined Ocean processes including winter-to-winter reemergence of SST anomalies, subduction, ENSO teleconnections and Indian Ocean SST variability.

Reemergence and subduction are active model processes, while ENSO teleconnections are impacted by the excessive westward extent of El Niño/La Niña events in the model.

Clara Deser (NCAR): North Pacific decadal variability
There is robust decadal (14-18 yr) variability of SST and subsurface temperature in the Kuroshio extension region. Ocean dynamics appears to play a key role in this variability. The atmospheric response to the SST anomalies is positive, i.e. would act to reinforce the SST anomalies, but weak.

Joel Norris (UCSD Scripps): Extratropical clouds, related meteorological parameters
While CCSM2 reproduces the major features of the observed climatological extratropical low cloudiness over the oceans it does not reproduce the specific magnitude and location of subtropical stratocumulus. The negative relationship between SST and low cloud anomalies in summer are well simulated but the SLP-cloud correlations are much stronger than in nature.

Ben Kirtman (COLA): Asian-Australian Monsoon, links to ENSO
The Asian monsoon is simulated reasonably well. The lagged correlations between ENSO and the monsoon, with the monsoon leading, are in the correct sense but the amplitude and pattern differ from observations.

Ken Sperber (LLNL): MJO
CCSM2 Intraseasonal variability in the tropical Pacific/Indian Ocean sector is a factor of 2-3 times weaker than observations. Both CCSM2 and CAM2 do not have an MJO, i.e. eastward propagating waves with periods of 30-70 days are missing.

Aiguo Dai (NCAR): Diurnal Variability in CCSM2
CCSM2 simulates the diurnal cycle of SLP and surface air temperature over land reasonably well. The diurnal cycle of temperature and precipitation is too weak over the ocean. Precipitation frequency is reasonable but convective precipitation occurs ~2 hours earlier than in nature.

FUTURE PLANS

• Work closely with the AMWG and the OMWG to diagnose and improve the CCSM. Have a joint meeting with these working groups in early 2003, to better understand model error, e.g. why does the model continue to have a semi-annual cycle of SST in the tropical east Pacific.
• Continue the development of web pages for CCSM2 diagnostics.
  

Participant List

Michael Alexander
Caspar Ammann
Jeffrey Anderson
Julie Arblaster
Joseph Barsugli
John Bergman
Uma Bhatt
Cecilia Bitz
Maurice Blackmon
Gordon Bonan
Byron Boville
Esther Brady
Grant Branstator
Christopher Bretherton
Francis Bretherton
Bruce Briegleb
Frank Bryan
Lawrence Buja
Julie Caron
Robert Cess
Ping Chang
Clifford Chen
John Chiang
William Collins
Bruce Cornuelle
Tony Craig
Aiguo Dai
Gokhan Danabasoglu
Cecelia DeLuca
Clara Deser
Scott Doney
Leo Donner
C. Mark Eakin
David Erickson
Augustus Fanning
John Fasullo
Johannes Feddema
Inez Fung
Peter Gent
Richard Grotjahn
James Hack
Charles Hakkarinen
Alexander Hall
Howard Hanson
Matthew Hecht
Isaac Held
William Hibler
Elisabeth Holland
Marika Holland
Aixue Hu
Huei-Ping Huang
Elizabeth Hunke
James Hurrell
Takashi Ishii
Robert Jacob
Steven Jayne
Ming Ji
Jeffrey Kiehl
Ben Kirtman
Paul Kushner
William Large
JIalin Lin
Keith Lindsay
William Lipscomb
Michael MacCracken
James Mahoney
Brian Mapes
James McWilliams
Steve Meacham
Gerald Meehl
Philip Merilees
Nicole Molders
Richard Moritz
Sylvia Murphy
Sumant Nigam
Joel Norris
Jerry Olson
Adam Phillips
David Pierce
Taotao Qian
David Randall
Marilyn Raphael
Phillip Rasch
Michele Rienecker
Richard Rood
Anthony Rosati
James Rosinski
Benjamin Santer
Edward Sarackik
Ramalingam Saravanan
Fabrizio Sassi
Dave Schimel
Edwin Schneider
Julie Schramm
Oyvind Seland
Olga Sergienko
Anji Seth
Jacob Sewall
Christine Shields
Richard Smith
Amy Solomon
Kenneth Sperber
Pamela Stephens
Max Suarez
Dezheng Sun
Eric Sundquist
Karl Taylor
Starley Thompson
Peter Thornton
Keven Trenberth
Stephen Vavrus
Ilana Wainer
Warren Washington
Christine Wiedinmyer
David Williamson
Xiaoqing Wu
Xubin Zeng