Mechanisms of summertime subtropical Indian Ocean sea surface temperature variability

It is well known that some warm season subtropical Indian Ocean sea surface temperature (SST) variability correlates with rainfall over certain regions of southern Africa that depend on rainfall for their economic well being. The mechanism for this SST variability is reconsidered. The prevailing hypothesis has been that zonal wind speed variability, affecting latent heat flux, is the dominant process. Results from analyses of observed SST, operational air-sea fluxes and simple atmospheric boundary layer physics are used here to show, however, that meridional atmospheric advection of near surface water vapor plays a dominant role in creating this type of southern subtropical Indian Ocean SST variability. Bi-modal changes in the position of the subtropical atmospheric anticyclone are responsible for the anomalous advection.