Seasonal and Interannual Variations of the SST above the Seychelles Dome

Abstract

he seasonal and interannual variations of the sea surface temperature (SST) above the Seychelles Dome (SD) are investigated using outputs from an OGCM. The SST warms from August to April and cools from May to July. The surface heat flux plays the most important role in the seasonal variation, and it is mostly due to shortwave radiation. The horizontal advection tends to warm the SST in austral winter owing to the southward Ekman heat transport associated with the Indian summer monsoon. The cooling by the vertical turbulent diffusion becomes most effective in austral summer owing to the thin mixed layer during that time. On the interannual time scale, the SST becomes anomalously warm (cool) when the SD is weak (strong). In contrast to the seasonal variation, the vertical diffusion plays the most important role and causes anomalous warming (cooling). This warming (cooling) is due to the anomalously warm (cold) water below the mixed layer as a result of the deeper (shallower) thermocline in response to ocean dynamics. Also, the cooling by the vertical diffusion becomes less (more) efficient, because the mixed layer is anomalously thick (thin). The horizontal advection contributes to the anomalous warming (cooling) due to the anomalous southward (northward) Ekman heat transport. On the other hand, the anomalous surface heat flux tends to cool (warm) the mixed layer, because the warming of the mixed layer by the shortwave radiation becomes less (more) efficient due to the anomalously thick (thin) mixed layer.