CONVECTION-EVAPORATION FEEDBACK IN THE EQUATORIAL PACIFIC

The coupling between convection and surface evaporation is investigate d to assess the importance of evaporative cooling in regulating the tr opical sea surface temperature. It is found that such a coupling is sc ale dependent. On timescales of several days, convective activity enha nces surface evaporation, which together with the decrease of surface solar radiation, acts to cool the sea surface, However, on scales of c limatic interest, convection acts to reduce surface evaporation. High sea surface temperature gives rise to more convective activity, which through interaction with the large-scale circulation, increases the lo w-level large-scale convergence and decreases the surface wind, leadin g to low evaporation in spite of the increased surface-air humidity di fference. Therefore, although individual convective events can signifi cantly enhance surface evaporation on short timescales, the long-term average effect of convection is to suppress surface evaporation at hig h SST due to its interaction with the large-scale circulation. One pot ential implication of this result is that evaporative cooling on clima te timescales may not provide a negative feedback on the sea surface t emperature of warm oceans with convectively disturbed tropospheres.