THEORETICAL CLIMATE DYNAMICS GROUP
UCLA's IEM 4 Abstract

Model Evaluation

TCD
home		 DA DAMEE IEM3 IEM4
DA

Model Evaluation Experiments and Parameter Estimation for the North Atlantic Basin Using the GFDL MOM

Michael Ghil(*,**), Chung-Chun Ma(*),
Kayo Ide(*,**), C. Roberto Mechoso(*)

(*) Department of Atmospheric Sciences and
(**) Institute of Geophysics and Planetary Physics,
University of California, Los Angeles, CA 90095-1565, U.S.A.

Our ultimate goal is to build a comprehensive data assimilation system to nowcast and forecast mesoscale oceanic motions on the synoptic time scale in a coupled ocean-atmosphere model. This requires: i) modeling regional and basin-scale oceanic processes, and their coupling to the atmosphere's general circulation, ii) designing a sophisticated but efficient data assimilation procedure that includes observing-system optimization, and iii) studying the phenomena that play a major role in the North Atlantic Basin's ocean-only and coupled dynamics. All the components of this comprehensive system must be carefully examined individually and then optimally combined for successful now- and forecasting.

In the UCLA analysis-and-forecast system, the three-dimensional oceanic circulation's evolution is modeled using the GFDL Modular Ocean Model (MOM). For the climatology experiment of the Data Assimilation and Model Evaluation Experiments--North Atlantic Basin (DAMEE-NAB) with 0.5 deg. X 0.5 deg. horizontal resolution, the model has 15 layers in the vertical -- of which 7 layers are in the first 300 m, to help resolve the turbulent mixing processes in the upper ocean -- and uses the Mellor and Yamada (1982) parameterization for vertical mixing. Two computational domains, 9--47 deg. N and 3--61 deg. N with 3 deg. wide buffer zones at the northern and southern boundaries each, are chosen to examine the effect of the domain size on the Gulf-Stream System's behavior. The smaller domain agrees with the DAMEE-NAB specifications, as do the bathymetry and surface forcing. To cope with the incompleteness of the temperature-salinity data sets for the initialization and buffer-zone boundary conditions, the GDEM/Lozier (1995) data are injected into a complete Levitus (1982) data set wherever available. The model requires 7.4 and 9.5 MW in memory on C90 and a 10-year run takes 50 and 70 CPU hours for the smaller and larger domain respectively.

The climatological analysis of the results will be shown for the smaller-domain run, according to the DAMEE specifications. We will present E-W and N-S temperature and salinity sections, at 27 deg. N and 55 deg. W respectively, as well as the Florida current transport and the kinetic energy of the flow as a function of time. Preliminary results will be also discussed for temporal variability of Gulf-Stream's north wall position as derived from the model's 15 deg. C isotherm contour at 200 m depth These results suggest that the present model provides a sound basis for the planned comprehensive data-assimilation system to now- and forecast mesoscale ocean features at higher horizontal and vertical resolution.

Figure Caption Monthly-mean Gulf-Stream paths derived from the 15 deg. C isotherm contour at 200 m depth for the last three years of the 10-year run. The interior rectangle indicates the DAMEE-NAB validation domain.

[ TCD home | DA | DAMEE | IEM3 | IEM4 DA ]
April 1, 1997