The role of heat fluxes and moist static energy in tropical convergence zones

Abstract

The relationship between monthly mean outgoing longwave radiation (OLR) and the mean moist static energy of the lower troposphere is shown to be similar to the relationship between monthly mean OLR and sea surface temperature over the oceanic regions. The relationship between monthly mean OLR and surface moist static energy shows that the threshold value for the onset of convection is different in continental and oceanic regions. However, the threshold of moist static stability for the troposphere (surface to 400 mb) is the same for oceans and continents. This relationship is consistent with the simple model of the tropical convergence zones proposed by Neelin and Held. The net energy convergence in the troposphere was found to be positive in regions with OLR below 210 W m^-2. This result is consistent with the Neelin and Held hypothesis that the necessary but not sufficient condition for the existence of tropical convergence zone is a positive energy convergence in the troposphere.