Search Results
Abstract
An approximate mass (volume) budget in the surface layer of the Southern Ocean is used to investigate the intensity and regional variability of the ventilation process, discussed here in terms of subduction and upwelling. Ventilation resulting from Ekman pumping is estimated from satellite winds, the geostrophic mean component is assessed from a climatology strengthened with Argo data, and the eddy-induced advection is included via the parameterization of Gent and McWilliams, together with eddy mixing estimates. All three components contribute significantly to ventilation. Finally, the seasonal cycle of the upper ocean is resolved using Argo data.
The circumpolar-averaged circulation shows an upwelling in the Antarctic Intermediate Water (AAIW) density classes, which is carried north into a zone of dense Subantarctic Mode Water (SAMW) subduction. Although no consistent net production is found in the light SAMW density classes, a large subduction of Subtropical Mode Water (STMW) is observed. The STMW area is fed by convergence of a southward and a northward residual meridional circulation. The eddy-induced contribution is important for the water mass transport in the vicinity of the Antartic Circumpolar Current. It balances the horizontal northward Ekman transport as well as the vertical Ekman pumping.
While the circumpolar-averaged upper cell structure is consistent with the average surface fluxes, it hides strong longitudinal regional variations and does not represent any local regime. Subduction shows strong regional variability with bathymetrically constrained hotspots of large subduction. These hotspots are consistent with the interior potential vorticity structure and circulation in the thermocline. Pools of SAMW and AAIW of different densities are found along the circumpolar belt in association with the regional pattern of subduction and interior circulation.
Abstract
An approximate mass (volume) budget in the surface layer of the Southern Ocean is used to investigate the intensity and regional variability of the ventilation process, discussed here in terms of subduction and upwelling. Ventilation resulting from Ekman pumping is estimated from satellite winds, the geostrophic mean component is assessed from a climatology strengthened with Argo data, and the eddy-induced advection is included via the parameterization of Gent and McWilliams, together with eddy mixing estimates. All three components contribute significantly to ventilation. Finally, the seasonal cycle of the upper ocean is resolved using Argo data.
The circumpolar-averaged circulation shows an upwelling in the Antarctic Intermediate Water (AAIW) density classes, which is carried north into a zone of dense Subantarctic Mode Water (SAMW) subduction. Although no consistent net production is found in the light SAMW density classes, a large subduction of Subtropical Mode Water (STMW) is observed. The STMW area is fed by convergence of a southward and a northward residual meridional circulation. The eddy-induced contribution is important for the water mass transport in the vicinity of the Antartic Circumpolar Current. It balances the horizontal northward Ekman transport as well as the vertical Ekman pumping.
While the circumpolar-averaged upper cell structure is consistent with the average surface fluxes, it hides strong longitudinal regional variations and does not represent any local regime. Subduction shows strong regional variability with bathymetrically constrained hotspots of large subduction. These hotspots are consistent with the interior potential vorticity structure and circulation in the thermocline. Pools of SAMW and AAIW of different densities are found along the circumpolar belt in association with the regional pattern of subduction and interior circulation.
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).
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).
