Variability of the mixed layer depth over the North Pacific simulated from a global OGCM with three different vertical mixing schemes

Abstract

Seasonal variability of the mixed layer depth (MLD) over the North Pacific has been investigated using global ocean general circulation model (OGCM) simulations with three different vertical mixing schemes, based on comparisons among model simulations, as well as comparison with the MLD climatology derived from Levitus data. The OGCM used is GFDL MOM1.1, and has been forced for about 30 years, using monthly-mean climatological wind, heat flux plus restoring, and restoring of the model sea surface salinity to Levitus data. All vertical mixing schemes have successfully captured the well-known distinct patterns of seasonal variations of MLD, which are considerably large in mid-latitude and marginal in equatorial regions, while producing notable discrepancy on the seasonality at high latitudes. The presence of a large value of MLD around Kuroshio region in winter is qualitatively well reproduced independently of vertical mixing schemes, although the model MLD tends to be larger than the MLD climatology. Convection parameterization with a large value of vertical eddy diffusivity has been found to produce a false deep mixed layer in Kuroshio region in spring, implying the importance of a proper parameterization of convection in realistic simulation of the MLD in an OGCM