Joint Session J2J.6 Kinematic and microphysical characteristics of a stratiform rain band observed in Tropical Storm Gabrielle at landfall

Monday, 24 October 2005: 5:00 PM
Alvarado ABCD (Hotel Albuquerque at Old Town)
Dong-Kyun Kim, Univ. of Alabama, Huntsville, AL; and K. R. Knupp

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Kinematic and microphysical structures of an intense stratiform rainband observed during the landfall of Tropical Storm Gabrielle are examined. On 14 September 2001 Tropical Storm Gabrielle made landfall along the west coast of Florida. Detailed observations of Gabrielle were made by Mobile Integrated Profiling Systems (MIPS), a SMART-R radar located near the MIPS, and the Tampa Bay WSR-88D radar located 60 km to the north. Kinematic computations of horizontal divergence and vertical air motion were obtained from both 915 MHz wind profiler measurements and EVAD analyses applied to the SMART-R data. Mesoscale divergence is estimated from the profiler data by using all five beams to determine variations in horizontal wind between opposing off-zenith beams. Strong convergence was measured near the melting layer where relatively intense cooling by melting particles occurred. Weak divergence was measured within the 6-10 km AGL layer and near the surface. Vertical air motions were close to zero in the vicinity of the melting layer and increased towards upper levels, promoting ice particle growth. The weak mesoscale ascent at mid- and upper levels is characteristic of the profiles of vertical air velocity in the stratiform regions of mesoscale convective systems. Increasing downward air motions associated with precipitation evaporation and mesoscale downdrafts was observed at lower levels. The profiler analysis is compared with the EVAD analysis applied to the SMART-R data. The vertical motion and terminal fall speed profiles obtained by these two methods are used to refine the retrieval of drop size distributions (derived from the profiler Doppler spectra) below the melting level, and ice particle size distributions above the melting level. We will investigate the kinematic properties of divergence as a key factor affecting the profiles of the heating above the melting layer and cooling below it within a stratiform precipitation.

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