On the Heat Balance of the Walker Circulation

The heat budget of the Walker circulation near 10°S is studied. The primary drive for the circulation is the heating due to zonal variations in condensation. The relative heating and cooling at different longitudes is balanced approximately by adiabatic cooling and heating due to rising and sinking motions. In the region where the condensation heating is a maximum two different analyses indicate that the evaporation is a minimum, even though the sea surface temperature is a maximum. This is because the surface heating is dominated by the insolation, which is a minimum in the region of enhanced condensation where the cloud cover is a maximum. This implies that the region of enhanced condensation is associated with a region of moisture convergence rather than with a region of enhanced evaporation, and that the sea surface temperature gradients only play a secondary role in forcing the Walker circulation.