The moisture flux convergence in the sub-cloud layer forced by vertical diffusion of heat and condensational heating are found to be in phase over the ocean and 180 degrees out of phase over the land. Over the ocean, both of these forcings contribute to time mean moisture flux convergence in the regions of large precipitation. Over the land, the condensational heating leads to moisture flux convergence in the regions of large precipitation while the vertical diffusion of heat leads to moisture flux divergence. This indicates that the motions forced by the surface temperature provide a negative feedback on the precipitation. This feedback is apparently due to the relatively cool surface temperatures which are present in the regions of large precipitation over land. This locally cool surface temperature leads to a low level high pressure region which is divergent near the surface. Other forcing functions are shown to play a minor role in the time mean moisture budget with the exception of the orographic forcing in some regions.
The lowest model sigma level wind field over the tropical Pacific Ocean is examined. In general both the zonal and meridional wind fields are dominated by the response to convective condensational heating. Exceptions include the meridional wind along the western coasts of the tropical continents and the zonal wind along the equator. In these regions, the response to low level temperature gradients is found to be non-negligible in comparison with the response to convective condensational heating. The role of the orographic forcing is also significant along the coasts of the tropical continents.
last update: 25 July 1995
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