Accession Number : ADA133309

Title :   Cumulus Momentum Transports in Tropical Cyclones,


Personal Author(s) : Lee,Cheng-Shang

PDF Url : ADA133309

Report Date : May 1982

Pagination or Media Count : 87

Abstract : The net influence of sub-grid or smaller unresolvable scale processes (which cannot be directly detected from conventional observations) on the tangential momentum field in tropical cyclones has been calculated as a residual from the grid-scale momentum budgets of sixteen rawinsonde composite data sets. Results show that cyclone systems of the Pacific and Atlantic that are undergoing development have similar residual profiles in the vertical: positive cyclonic acceleration at upper and lower levels and negative cyclonic acceleration at between levels. Stronger systems have a greater magnitude of the sub-grid scale effect. These results are believed to represent primarily the cumulus convective transport (defined as cumulus friction). A simple cloud model is developed to diagnose momentum rearrangement in the vertical through mass recycling. Model results agree well with the residual calculations from the composites. The total convective effect (TCE) on the tangential momentum includes the vertical transports by all the upward and downward motions which can be decomposed into the mean vertical motion and the local mass recycling. This TCE is found to reduce both the low level cyclonic and the upper level anticyclonic winds. These results imply that the net effect of the cumulus convective transport is down-gradient and acts to reduce the vertical wind shear of the cyclone. This mutual interaction between the cumulus convection and the larger scale flow features and their possible influence on tropical cyclone development is discussed. (Author)

Descriptors :   *Tropical cyclones, *Convection, Cumulus clouds, Momentum, Friction, Wind, Transport

Subject Categories : Meteorology

Distribution Statement : APPROVED FOR PUBLIC RELEASE