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Report of the CSM Ocean Model Working Group Meeting

Fourth Annual Climate System Model Workshop

by Michael Spall and Peter Gent, Working Group Co-chairs

Breckenridge, Colorado

June 23, 1999


The CSM Ocean Model Working Group met on the morning of June 23, 1999, at the Fourth Annual Climate System Model Workshop in Breckenridge, Colorado. The discussions covered issues of model development, application of NCAR CSM Ocean Model (NCOM) to science problems, and plans for future improvements.

Following on recommendations from the 1998 Annual CSM Workshop and the winter 1999 CSM Ocean Working Group meeting, physics from NCOM 1.4 are continuing to be implemented into the POP-based ocean code. Benchmarks for idealized and global POP configurations are essentially complete. Mathew Hecht (NCAR) presented results from flat bottom sector model calculations using both NCOM 1.4 and POP codes. Systematic comparisons indicate that the POP code is able to reproduce closely the results from NCOM 1.4. The thermocline in POP is slightly sharper as a result of a less diffusive implementation of the Gent-McWilliams eddy flux parameterization compared to the original form incorporated into NCOM 1.4. The POP model is also being tested on the x3' global grid. Although the model has not yet been run to equilibrium, Rick Smith (LANL) showed that the surface fluxes and transports compare closely with previous x3 NCOM global integrations. Differences found in the Arctic regions are expected because of the improved numerical representation of the high latitudes in POP.

An upper ocean version of the NCOM (UOM) has been developed and tested by Jim McWilliams (UCAR/NCAR) and Gokan Danabasoglu (NCAR). The primary advantages of this approach are: rapid equilibration, numerical efficiency, option of terrain following coordinates with reduced truncation errors related to steep and tall topography, and increased resolution of the bottom boundary layer near sill overflows. The model is appropriate for the study of upper ocean variability on timescales of seasonal up to decadal. The UOM is able to reproduce both the mean fields (circulation, hydrography) and their variability on seasonal-to-interannual timescales when compared to a full depth ocean model. The initial testing of the model is complete and it is now available as a tool to interested users.

Model development issues to be addressed in the coming year were also discussed. Physics packages for anisotropic viscosity, bottom boundary layers, fresh water budgets in marginal seas, and biogeochemistry have already been implemented in NCOM and were recommended to be incorporated into POP. Several improvements in physics and numerics were identified and recommended for implementation in both NCOM and POP. These include spatially variable (depth and position) vertical viscosity and vertical diffusivity, spatially variable eddy diffusivity coefficient, and partial bottom cells for more accurate treatment of bottom topography.

A 40-year integration of the x2' NCOM global model (1958-1997) is complete and initial evaluation of the mean and low-frequency variability in the North Pacific is underway. JoAnne Lysne (NCAR) found that the mean model temperature within the main thermocline was within 1-2 deg C of the climatological hydrography over the North Pacific. The model also showed similar patterns of low-frequency variability in temperature. Differences between time periods 1965-1976 and 1977-1997 show basin scale changes in hydrographic properties that may be related to changes in the wind stress patterns. Antonietta Capotondi (CDC) found that the NCOM model is able to reproduce many aspects of the observed formation, subduction, and propagation of temperature and salinity anomalies in the main thermocline of the North Pacific during the period 1972-1994. Analysis is underway to understand how these anomalies propagate from mid-latitudes towards the equator and their influences on the large-scale circulation. The output from this calculation is available to the user community for analysis.

List of Participants:

David Bader, Pacific Northwest National Laboratory
Johanna Balle-Beganton, Center for Atmospheric Sciences
David Battisti, University of Washington
Jason Bell, Lawrence Livermore National Laboratory (LLNL)
Thomas Bettge, NCAR
Uma Bhatt, International Arctic Research Center
Maurice Blackmon, NCAR
Rainer Bleck, Los Alamos National Laboratory (LANL)
Byron Boville, NCAR
Esther Brady, NCAR
Marcia Branstetter, University of Texas
Frank Bryan, NCAR
Kenneth Caldeira, Lawrence Livermore National Laboratory
Maria-Antonietta Capotondi, NOAA-CIRES
Ping Chang, Texas A&M University
Yi Chao, Jet Propulsion Lab
Wei Cheng, University of Miami
Wooyoung Choi, Los Alamos National Laboratory
Shaoping Chu, Los Alamos National Laboratory
Gokhan Danabasoglu, NCAR
John Davis, Los Alamos National Laboratory
Sumner Dean, Los Alamos National Laboratory
Scott Doney, NCAR
Philip Duffy, Lawrence Livermore National Laboratory
C. Mark Eakin, NOAA
Scott Elliott, Los Alamos National Laboratory
Peter Eltgroth, Lawrence Livermore National Laboratory
John Farrara, UCLA
Avijit Gangopadhyay, University of Massachusetts
Peter Gent, NCAR
Stephen Griffies, GFDL
Cecile Hannay, IARC Frontier University of Alaska
Matthew Hecht, NCAR
Marika Holland, NCAR
William Holland, NCAR
Steven Jayne, NCAR
Philip Jones, Los Alamos National Laboratory
Brian Kauffman, NCAR
Joan Kleypas, NCAR
Chung-Chieng Lai, Los Alamos National Laboratory
Xin-Zhong Liang, Illinois State Water Survey
Keith Lindsay, NCAR
William Lipscomb, Los Alamos National Laboratory
Ferial Louanchi, Pennsylvania State University
JoAnn Lysne, NCAR
Robert Malone, Los Alamos National Laboratory
Mathew Maltrud, Los Alamos National Laboratory
Julie McClean, Naval Postgraduate School
James McWilliams, UCLA/NCAR
Jose Milovich, Lawrence Livermore National Laboratory
Arthur Mirin, Lawrence Livermore National Laboratory
Richard Moritz, University of Washington
Sylvia Murphy, NCAR
Norikazu Nakashiki, NCAR
Linda Peters, Lawrence Livermore National Laboratory
William Peterson, Pennsylvania State University
David Pierce, Scripps Institution of Oceanography
Chris Poulsen, Pennsylvania State University
Andrey Proshutinsky, University of Alaska Fairbanks
Todd Ringler, Colorado State University
Daniel Robitaille, Lawrence Berkeley National Laboratory
Anthony Rosati, GFDL
Albert Semtner, Naval Postgraduate School
Richard Smith, Los Alamos National Laboratory
Michael Spall, Woods Hole Oceanographic Institution
Michael Steele, University of Washington
Shan Sun, NASA/Goddard Institute for Space Studies
Stephen Vavrus, University of Wisconsin
Dailin Wang, University of Hawaii
Huaxiao Wang, Lawrence Livermore National Laboratory
Zong-Liang Yang, University of Arizona
Stephen Yeager, NCAR
Stephen Zebiak, IRI
Jinlun Zhang, University of Washington
Yuxia Zhang, Naval Postgraduate School