Convection-Evaporation Feedback in the Equatorial pacific

Abstract

The coupling between convection and surface evaporation is investigated to assess the importance of evaporative cooling in regulating the tropical sea surface temperature. It is found that such a coupling is scale dependent. On timescales of several days, convective activity enhances surface evaporation, which together with the decrease of surface solar radiation, acts to cool the sea surface, However, on scales of climatic 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 low-level large-scale convergence and decreases the surface wind, leading to low evaporation in spite of the increased surface-air humidity difference. Therefore, although individual convective events can significantly enhance surface evaporation on short timescales, the long-term average effect of convection is to suppress surface evaporation at high SST due to its interaction with the large-scale circulation. One potential implication of this result is that evaporative cooling on climate timescales may not provide a negative feedback on the sea surface temperature of warm oceans with convectively disturbed tropospheres.