Seasonal Near-Surface Dynamics and Thermodynamics of the Indian Ocean and Indonesian Throughflow in a Global Ocean General Circulation Model

Abstract

The near-surface dynamics and thermodynamics of the Indian Ocean are examined in a global ocean general circulation model (OGCM) with enhanced tropical resolution. The model uses a Seager-type heat flux formulation (weak relaxation toward a fixed SST, flux-corrected toward seasonal observed values). Resulting seasonal patterns of surface heat flux, mixed layer depth, and surface steric height all compare quite well with observations in the Indian Ocean, away from western boundaries. Distribution of flow in the mean Indonesian Throughflow is quite well simulated in the top 700 m. The model Indonesian throughflow transports, on average, 16.3 ? 106 m3 s?1 from the Pacific to the Indian Ocean, and its magnitude is fairly well predicted seasonally by the instantaneous Sverdrup version of the ?Island Rule.? Model geostrophic transports relative to 700 m are substantially smaller, with a different seasonal cycle. Observed geostrophic transports are smaller than those in the model, though the model reproduces the seasonal cycle well. The annual mean heat transport through the Indonesian Throughflow region (about 1.15 ? 1015 W) represents a heat sink for the Pacific Ocean and is an important heat source for the Indian Ocean. The authors have introduced an empirically based representation of tidal mixing in the Indonesian region: it causes water mass transformation through the Indonesian seas qualitatively like that observed and improves the realism of the surface heat fluxes. It also affects both the Indian and Pacific Oceans and causes extensive subsurface temperature and salinity changes in the former (i.e., cooling of the mixed layer, warming of the upper thermocline).