Fundamental Moist Modes of the Equatorial Troposphere

Abstract

Raymond's diabatic parameterizations are combined with a three-dimensional channel model on an equatorial beta plane. The equatorially symmetric moist modes of this model for an atmosphere initially at rest are ?nonlinear WISHE? (wind-induced surface heat exchange) modes. These modes are driven by the enhanced sea?air fluxes of entropy produced by self-generated westerly winds. Two varieties of these modes are found, those which move to the east at 8 m s?1 and those which move to the west at 4 m s?1. In both modes heavy rain occurs in air that has been moistened by convection of low precipitation efficiency. This preconditioning introduces a phase shift of several days between strong surface entropy fluxes into an air column and the heaviest rainfall. This phase shift may be responsible for the relatively low modal propagation speeds compared to those seen in other models. The modes identified in simulations with uniform sea surface temperature play a fundamental role in a simulation with a warm-pool-like sea surface temperature anomaly. The authors tentatively identify the simulated modes with Nakazawa?s ?superclusters.?