12C.2 The Response of Tropical Cyclone Precipitation to Environmental Forcing

Wednesday, 30 April 2008: 3:45 PM
Palms H (Wyndham Orlando Resort)
Matthew T. Wingo, The University of Alabama in Huntsville, Huntsville, AL; and D. J. Cecil

This study investigates how environmental factors influence the precipitation field of tropical cyclones. Environmental variables are computed using the ECMWF ERA40 model data from 1987-2002 and the ECMWF initial field values from 2002-2005. The precipitation field dataset is constructed from a large sample size of satellite-derived rain rates via passive microwave radiometers (SSMI, TMI, AMSRE) from 1987 to 2005, using the Remote Sensing Systems retrievals.

Composite rain rates are constructed as a function of varying environmental parameters such as shear, SST, and moisture convergence. These composites illustrate the spatial distribution and magnitude of tropical cyclone rain rates as a function of the environment.

Initial results using shear predictors from the SHIPS model (based on NCEP-NCAR reanalysis and GFS model) agree with previous studies. Weakly sheared tropical cyclones (less than 5 m/s) maintained a reasonably symmetric precipitation field, while moderately sheared (5-10 m/s) cases exhibited an asymmetric appearance. Strongly sheared (greater than 10 m/s) systems boasted the greatest asymmetry. The asymmetry was also a function of storm intensity, which decreased with increasing storm intensity for all shear values. In other words, tropical storms were the most asymmetric while major hurricanes (category 3 and above) were the most symmetric for all shear values. For all cases of storm and shear intensities, the precipitation field was displaced downshear and left of the shear vector.

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