CCSM Climate Variability Working Group Report
9 July 2004
Eldorado Hotel, Santa Fe, New Mexico

The Climate Variability Working Group met in the Eldorado Hotel in Santa Fe on Friday, July 9, 2004. The meeting consisted of 11 oral presentations, followed by a business discussion led by co-chair Clara Deser. Nine of the presentations and the business discussion are available as powerpoint files (see links by author below). The presentations by Dr. Sumant Nigam and Dr. Marilyn Raphael are summarized in textual format.

Presentations

Alfredo Ruiz-Barradas and Sumant Nigam, University of Maryland
Warm season hydroclimate variability over the Great Plains in observations, reanalysis, and AMIP simulations

The interannual variability of Great Plains precipitation was analyzed in the warm-season months using gridded observations, satellite-based precipitation estimates, NCEP and ERA-40 reanalysis data, and the half-century long NCAR/CAM and NASA/NSIPP atmospheric model simulations. Regional hydroclimate is the focus because of its immense societal impact, and because the involved variability mechanisms are not well understood. (The variability analysis was preceded by an examination of the precipitation annual-cycle over the U.S., specially, its representation in the CAM2 and CAM3 simulations; CAM3 shows an improved annual-mean over the central and southeastern U.S., but the annual-cycle there is, unfortunately, further degraded.)

We find that Great Plains precipitation variability is represented rather differently, and only quasi-realistically, in the reanalyses. NCEP has larger amplitude but less traction with observations in comparison with ERA-40. Model simulations exhibit even greater amplitude-spread, with NSIPP's being larger than NCEP's, and CAM2's being smaller than ERA-40; CAM3's amplitude is more reasonable, however. But the simulated variability is uncorrelated with observations, in both models; monthly correlations are smaller than 0.10 in all cases.

Closer examination reveals that models generate nearly all of their Great Plains precipitation from deep convective processes, whereas ERA-40 suggests that stratiform contribution is, at least, as important as the convective one. An assessment of the regional atmosphere water-balance is also revealing: stationary moisture-flux convergence accounts for most of the Great Plains variability in ERA-40, but not in the NCEP reanalysis and model simulations; convergent fluxes generate less than half of the precipitation in the latter; local evaporation does the rest in models.

Phenomenal evaporation in the models - up to four-times larger than the highest observationally constrained estimate (NCEP's) - provides bulk of the moisture for Great Plains precipitation variability, i.e., precipitation-recycling is very efficient in models; perhaps, too efficient, specially in the NSIPP and CAM3 models.

Remote water sources contribute substantially to Great Plains hydroclimate variability in nature via fluxes. Getting the interaction pathways right is presently challenging for the models.

Christophe Cassou, CERFAX, Toulouse
CAM2 coupled to a mixed layer ocean model: Model physics and climate variability

Young-Oh Kwon, NCAR
Decadal ocean/atmosphere variability in the North Pacific in CCSM2

Jialin Lin, Climate Diagnostics Center
The MJO problem in GCMs: What is the missing physics?

Grant Branstator, NCAR
Climate change from the perspective of modes of variability

Marilyn Raphael, UCLA
Zonal wave 3 contribution to climate variability in the Southern Hemisphere

Zonal wave 3 (ZW3) is the asymmetric part of the large-scale atmospheric circulation associated with meridional flow in the extra-tropical Southern Hemisphere (SH). It is quasi-stationary and it contributes 8% of the spatial variance in the field reaching a maximum near 50S. An index of ZW3 was created from the NCAR-NCEP Reanalyses, 1979-2001, and used to explore the influence of the large-scale atmospheric circulation on Antarctic sea-ice concentration (SIC). ZW3 was correlated with SIC data from which the annual cycle was removed. The resulting pattern of moderately large negative and positive correlation coefficients has a well-defined zonal wave 3 signature, which suggests that zonal wave 3 has a strong influence on the interannual variability of SIC. This was discussed in terms of the local surface and air temperature anomalies associated with ZW3.

Jim Hurrell, NCAR
Attribution of Atlantic climate variability and change

Clara Deser, NCAR
ENSO variability and atmospheric teleconnections in CCSM3

R. Saravanan, NCAR
Tropical Atlantic variability in CCSM3/CAM3

Mike Alexander, NCAR (presentation given by Clara Deser)
Extratropical air-sea interaction in CCSM3

Ed Schneider, COLA
ENSO-monsoon relationships in CCSM3

Clara Deser, NCAR
Business Discussion

Attendees (not a complete list):
Bruce Anderson Boston University
Grant Branstator NCAR
Amy Braverman Jet Propulsion Laboratory
Christophe Cassou CERFACS
Clara Deser NCAR
David DeWitt Columbia University
Gerald Geernaert Los Alamos National Laboratory
Huei-Ping Huang Lamont-Doherty Earth Observatory
James Hurrell NCAR
Ming Ji NOAA
Renu Joseph University of Maryland
Daniel Kirk-Davidoff U. Maryland College Park
Young-Oh Kwon NCAR
David Legler U.S. CLIVAR Office
Jialin Lin University of Colorado
David Mansbach Scripps Institution of Oceanography
Sumant Nigam University of Maryland
Adam Phillips NCAR
David Pierce Scripps Institution of Oceanography
Marilyn Raphael University of California Los Angeles
Michele Rienecker Global Modeling and Assimilation Office
Alfredo Ruiz-Barradas University of Maryland
Ramalingam Saravanan NCAR
Edwin Schneider George Mason University/COLA
Zewdu Segele University of Oklahoma
Anji Seth Columbia University
De-Zheng Sun University of Colorado
Joe Tribbia NCAR
Faming Wang University of Texas at Austin
Andrew Wittenberg NOAA Geophysical Fluid Dynamics Laboratory
Lixin Wu Center For Climatic Research