Local mixed layer response to wind and buoyancy forcing in the western equatorial Pacific

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The behavior of three types of widely used one-dimensional mixed layer models (bulk, turbulence closure, and shear instability) is evaluated under idealized conditions representative of atmospheric forcing over the western equatorial Pacific Ocean. Results show that under heavy precipitation (frequently observed in this region), models with a shear instability mixing component capture the fundamental behavior of the mixed layer better than do those without. On the basis of this comparison, a version of the Price-Weller-Pinkel (PWP) [Price et al., 1986; Schudlich and Price, 1992] mixed layer model is selected for the purpose of simulating near-surface temperature and salinity measurements in this region. Heat and salt budgets calculated from observations taken during the Tropical Ocean Global Atmosphere-Coupled Ocean-Atmosphere Response Experiment (TOGA-COARE) pilot study suggest that above the top of the thermocline, local atmospheric forcing is indeed of first-order importance in the evolution of the temperature field. Horizontal advection of salt, however, is observed to be as important as local forcing (evaporation minus precipitation) in the evolution of the salinity field. Driven by observed fluxes, numerical simulation using the PWP model confirm the primary importance of local forcing for the temperature field and the importance of salinity advection for the salinity field. During the TOGA-COARE intensive observing period, simulated and observed temperatures agree well at 9 m depth under weak winds, but the model/data discrepancy gradually increases during periods of stronger westerly winds. The addition of a simplified meridional temperature advection term, based on the mean observed temperature gradient, reduces but does not eliminate the model data discrepancy. The magnitude of model/data salinity discrepancies is consistent with concurrent measurements of instantaneous horizontal salinity gradients and velocities, but not with their time-mean values. Copyright 1999 by the American Geophysical Union.

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Journal of Geophysical Research: Oceans





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