A 3-DIMENSIONAL OCEAN MESOSCALE SIMULATION USING DATA FROM THE SEMAPHORE EXPERIMENT - MIXED-LAYER HEAT-BUDGET

A primitive equation model is used to simulate the mesoscale circulati on associated with a portion of the Azores Front investigated during t he intensive observation period (IOP) of the Structure des Echanges Me r-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Expe rirnentale (SEMAPHORE) experiment in fall 1993. The model is a mesosca le version of the ocean general circulation model (OGCM) developed at the Laboratoire d'Oceanographie Dynamique et de Climatologie (LODYC) i n Paris and includes open lateral boundaries, a 1.5-level-order turbul ence closure scheme, and fine mesh resolution (0.11 degrees for latitu de and 0.09 degrees for longitude). The atmospheric forcing is provide d by satellite data for the solar and infrared fluxes and by analyzed (or reanalyzed for the wind) atmospheric data from the European Centre for Medium-Range Weather Forecasts (ECMWF) forecast model. The extend ed data set collected during the IOP of SEMAPHORE enables a detailed i nitialization of the model, a coupling with the rest of the basin thro ugh time dependent open boundaries, and a model/data comparison for va lidation. The analysis of model outputs indicates that most features a re in good agreement with independent available observations. The surf ace front evolution is subject to an intense deformation different fro m that of the deep front system, which evolves only weakly. An estimat e of the upper layer heat budget is performed during the 22 days of th e integration of the model. Each term of this budget is analyzed accor ding to various atmospheric events that occurred during the experiment , such as the passage of a strong storm. This facilitates extended est imates of mixed layer or relevant surface processes beyond those which are obtainable directly from observations. Surface fluxes represent 5 4% of the heat loss in the mixed layer and 70% in the top 100-m layer, while vertical transport at the mixed layer bottom accounts for 31% a nd three-dimensional processes account for 14%.