An Analysis of Subeloud-Layer Heat and Moisture Budgets in the Western Atlantic Trades

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  • 1 Department of Meteorology, University of California, Los Angeles 90024
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Abstract

Using rawinsonde, radiation, and surface heat and moisture flux data from the Barbados Oceanographic and Meteorological Experiment (BOMEX), the budgets of heat and moisture in the subcloud layer are calculated. The results show that the vertical eddy flux of dry static energy at the top of the mixed layer is small compared with the sensible beat flux at the sea surface during a relatively undisturbed period. The eddy flux of moisture at the top of the mixed layer is large and nearly balances the sea-surface evaporation. The large eddy moisture flux dominates the eddy flux of dry static energy across the top of the layer and results in a positive eddy buoyancy flux during relatively undisturbed synoptic conditions. For weakly unstable boundary layers topped by cumulus convection this suggests that the commonly used representation of the eddy buoyancy flux at the mixed layer top as a small negative fraction of the sea surface flux may be valid only in the environment away from the convection. Large cumulus cloud base mass fluxes computed using subcloud-layer information are consistent with the values obtained by Nitta using cloud-layer information for the same period.

Abstract

Using rawinsonde, radiation, and surface heat and moisture flux data from the Barbados Oceanographic and Meteorological Experiment (BOMEX), the budgets of heat and moisture in the subcloud layer are calculated. The results show that the vertical eddy flux of dry static energy at the top of the mixed layer is small compared with the sensible beat flux at the sea surface during a relatively undisturbed period. The eddy flux of moisture at the top of the mixed layer is large and nearly balances the sea-surface evaporation. The large eddy moisture flux dominates the eddy flux of dry static energy across the top of the layer and results in a positive eddy buoyancy flux during relatively undisturbed synoptic conditions. For weakly unstable boundary layers topped by cumulus convection this suggests that the commonly used representation of the eddy buoyancy flux at the mixed layer top as a small negative fraction of the sea surface flux may be valid only in the environment away from the convection. Large cumulus cloud base mass fluxes computed using subcloud-layer information are consistent with the values obtained by Nitta using cloud-layer information for the same period.

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