The residual mean circulation driven by tropical waves

The tropical upwelling circulation in the troposphere has two components, one driven by waves and one driven by zonal mean deep convective heating. The component driven by heating does not significantly extend above average cloud top height and does not contribute to transport across the tropical tropopause layer (TTL). Many different types of waves may contribute to the wave driven circulation, including extratropical planetary waves, synoptic scale eddies, and tropical waves driven by convective heating. Several recent studies have found that these tropical waves play an important role in modulating tropical tropopause temperatures and upwelling, with particular import for the water vapor entering the stratosphere.

We will discuss experiments using a time dependent primitive equation model forced by heating determined from TRMM rainfall rates. These experiments are designed to examine the transport circulation driven separately by stationary tropical waves, transient tropical waves, or synoptic scale eddies. The waves produced by the model are in good agreement ith waves observed by HIRDLS. Results show that tropical Rossby waves produce a much greater contribution to a residual mean vertical velocity across the TTL than the synoptic scale eddies. Also, the transient tropical Rossby waves are present at certain times of the year, and drive a significant residual circulation that extends higher in altitude than the circulation driven by stationary waves. The greater vertical extent of the circulation is due to an EP-flux divergence pattern that extends higher in altitude because transient waves can propagate higher into the lower stratosphere than stationary waves.