Report on the CCSM Atmosphere Model Working Group Meeting

Millennium Hotel, Colorado
Co-chairs: Bill Collins and Leo Donner
March 6 and 7, 2003

Outline

The meeting covered:

Recent developments in CAM since the release of CAM2 in May, 2003
Proposed changes to the physical parameterizations for the next release of CAM for use in NCAR's IPCC simulations
Effects of these proposed changes on the climate and simulation biases of CAM2
Release of the CAM2 scientific description
Release of a new diagnostics package for climate variability based upon WGNE standards
Release of a new 15-member ensemble of 50-year AMIP-style integrations of CAM
Analysis, diagnosis, and sensitivity experiments on the main systematic biases in CAM2
Update on the status of WACCM
Progress on testing superparameterization in CAM
Possibilities for using ARM data to evaluate and improve the model physics

The schedule of the talks and the introductory presentation regarding the status of CAM are available on the CCSM AMWG website.

Discussion of new model physics:

The proposed changes to moist physics have substantially reduced two of the main biases in the atmospheric model:

Overestimation of land surface temperatures in winter; and
Underestimation of tropical tropopause temperatures.

There were several suggestions for increasing the physical realism of the changes proposed to the prognostic cloud water and moist processes. These suggestions are now being tested in CAM.

Tuning experiments are underway with the Donner parameterization for deep cumulus. Global shortwave radiative balances are now quite close, and longwave balances are within 6 W/m². Current tuning is focusing on biases the Donner parameterization has introduced in water vapor in a few geographical regions between about 500 and 700 hPa and on total precipitation, especially in the west Pacific. The double ITCZ has largely been eliminated by the Donner parameterization, and the seasonal march of precipitation across the Equator in the tropical Pacific is in much better phase with observations than in CAM2.

The Bretherton diagnostic turbulence parameterization has been implemented and is currently undergoing testing in both CAM and SCAM. Preliminary results show sensitivity to entrainment processes and the large-scale vertical velocity field.

Discussion of new diagnostic frameworks:

The group agreed that additional diagnostics were needed to evaluate the cumulative effects of all the proposed changes. Several participants recommended that we evaluate the prototype of CAM2.x using Taylor diagrams. The co-chairs agreed to pursue this proposal with PCMDI, and the scientists at PCMDI have agreed to analyze CAM2.x using their diagnostic procedures. All the individual modifications are being diagnosed with the regular CAM2 package as test integrations are completed, and the results have been posted to the AMWG website. Two of the systematic biases in the model are:

Underestimation of tropical variability and poor representation of the Madden-Julian oscillation
Errors in the eastern Pacific related to boundary layer clouds and surface wind stress.

Although no breakthroughs were announced at the meeting regarding these problems, the AMWG has a couple of new tools for formulating and testing hypotheses. The first is the variability diagnostics package, and the second is the ability to output model history for individual model columns. This will greatly simplify comparison against field observations.

Other related models:

The co-chairs announced that a new Column Radiation Model (CRM) would be released to friendly users in April and to the community at the June meeting. The new CRM is based upon the CAM2 physics and Single Column Model (SCAM) client-server architecture. Its input is backward-compatible with the input used for the CCM3 CRM.

The AMWG voted that the SCAM be supported by the CCSM software engineering group. The SCAM will be updated for complete compatibility with the CAM2.0.2 code library, then released to the SE group.

Participants:

Tom Ackerman, PNNL
Mike Alexander, NOAA
Jeff Anderson, GFDL/NCAR
Julie Bacmeister, NASA
Dave Bader, DOE
John Bergman, NOAA
Byron Boville, NCAR
Jim Boyle, LLNL
Grant Branstator, NCAR
Chris Bretherton, U of Washington
Lawrence Buja, NCAR
Julie Caron, NCAR
Christophe Cassou, NCAR
Bill Collins, NCAR
Andrew Conley, NCAR
Gokhan Danabasoglu, NCAR
David DeWitt, COLA
Leo Donner, GFDL
Phil Duffy, LLNL
David Fillmore, NCAR
Jim Hack, NCAR
Tom Henderson, NCAR
Jim Hurrell, NCAR
Mike Iacono, AER Inc.
Jeff Kiehl, NCAR
Doug Kinnison, NCAR
Erik Kluzek, NCAR
Bill Large, NCAR
S-J. Lin, NASA
Eric Maloney, Oregon State U
Larry Marx, COLA
Jim McCaa, NCAR
Phil Merilees, NCAR
Sumant Nigam, U of Maryland
Jerry Olson, NCAR
Jerry Potter, LLNL
Dave Randall, Colorado State U
Phil Rasch, NCAR
Jim Rosinski, NCAR
Richard Somerville, Scripps
Mark Stevens, NCAR
Max Suarez, NASA
Dezheng Sun, NOAA
Rogoth Sundararajan, MIT
Karl Taylor, PCMDI
Kevin Trenberth, NCAR
John Truesdale, NCAR
Tom Wigley, NCAR
Dave Williamson, NCAR
Guang Zhang, Scripps
Minghua Zhang, SUNY-Stony Brook
Michal Ziemianski, NCAR
Menglin Jin, U of Maryland
Saravanan, NCAR
Maurice Blackmon, NCAR
Steve Reid, NSF
Warren Wahsington, NCAR
Bette Otto-Bliesner, NCAR
Natalie Mahowald, NCAR
Robert Pincus, NOAA
Jean-Francois Lamarque, NCAR
Jeff Yin, NOAA
Norm Wood, Colorado State U
Peter Hess, NCAR
Cecelia DeLuca, NCAR
Julia Lee-Taylor, NCAR
Joe Tribbia, NCAR
Kevin Raeder, NCAR