The Arabian Sea, Bay Of Bengal And South China Sea Seasonal Variation Of The Local Dynamic Process Is A Comparative Study

Dynamics of the seasonal cycle of sea surface height (SSH) in three low-latitude seas are studied using observations as well as numerical and theoretical models. Seasonal variability of the South China Sea (SCS) is interpreted in light of large-scale dynamics and Rossby waves. It is found that the seasonal cycle over most of the SCS basin is forced mainly by surface wind curl on baroclinic Rossby waves. Annual baroclinic Rosssby waves cross the basin in less than a few months, leaving the upper ocean in a quasi-steady Sverdrup balance. An anomalous cyclonic (anticyclonic) gyre is generated in winter (summer) by the anomalous cyclonic (anticyclonic) wind curl that is associated with the northeasterly (southwesterly) monsoon. In addition, surface heat flux acts to enhance the wind-generated variability. The winter (summer) surface cooling (warming) cools (warms) the mixed layer especially in the central SCS, reducing (increasing) the SSH.Seasonal variability of the Bay of Bengal (BOB) is shown to be forced dominantly by the surface wind curl on baroclinic Rossby waves, which seems similar to SCS. The smallness of the BOB ocean basin implies that the thermocline adjustment time to Rossby waves will be very short, so that the upper ocean can also satisfy quasi-steady Sverdrup balance. A cyclonic (anticyclonic) gyre in the northern BOB and an anticycloninc (cyclonic) gyre in the southern BOB are generated in summer (winter) by the southwesterly (northeasterly) monsoon. Except for surface wind curl, the gradient bottom topography also contributes significantly to the variation of SSH. The difference betweenηT /P and Levitusηsuggests that the bottom pressure contribution to the SSH is very important for seasonal variability in the BOB.Neither SCS nor BOB is similar to the dynamics of seasonal variability of Arabian Sea (AS). It seems that the dynamics of the seasonal cycle SSH in AS is mostly influenced by surface wind curl only in summer. An anticyclonic gyre is forced by the anticyclonic wind shear of the southwesterly summer monsoon in the southern part of the AS. But in winter, the low SSH seems to be mainly caused by sea surface heat flux cooling instead. In addition, the exchange flow through the southern open boundary between AS and Tropical Indian Ocean (TIO) contributes significantly to the variation of SSH all the year. The Somali boundary current forms a northward intrusion of TIO water into the southern AS except winter, causing an anticyclonic upper ocean circulation. This intrusion of water reverses in winter as well as the upper ocean circulation.