MECHANISMS OF SHORT-TERM SEA-SURFACE TEMPERATURE REGULATION - OBSERVATIONS DURING TOGA COARE

Analyses of ocean-atmosphere data from Tropical Oceans Global Atmosphe re Coupled Ocean-Atmosphere Response Experiment indicate that short-te rm (weekly to monthly) fluctuations of SST in the western Pacific warm pool are closely linked to the alternation of wet and dry spells driv en by the Madden-Julian oscillation (MJO). The dry phase is characteri zed by increased convection over the Indian Ocean, a prolonged period of atmospheric subsidence, and surface easterlies over the western Pac ific warm pool. During this phase, increased surface shortwave radiati on and reduced evaporation contribute about equally to the warming of the warm pool. Pronounced diurnal Variations in SST observed during th e dry phase may be instrumental in leading to the prolonged warming. T he dry phase is followed by the wet phase, in which the SST warming tr end is arrested and a cooling trend initiated by a reduction in surfac e shortwave radiation accompanying the buildup of organized convection . Subsequently, the continued cooling of the upper ocean is accelerate d by increased westerly surface wind leading to enhanced surface evapo ration and increased entrainment of cold water from below the thermocl ine. At this stage, the increased surface shortwave radiation due to t he diminished cloud cover from reduced convection opposes the cooling by evaporation. The cooling trend is reversed as soon as the westerly phase terminates and the dry phase is reinitiated by the establishment of new organized convection over the Indian Ocean. The authors' resul ts suggest that short-term SST variability in the western Pacific warm pool is closely linked to surface fluxes, which are strongly modulate d by atmospheric low-frequency variability associated with the MIG. Th e implications of the present results on the dynamics of the MJO and t he possible role of coupled SST in influencing the MJO variability are also discussed.