The vertical characteristics of raindrop size distributions and horizontal divergence in the stratiform regions of Hurricane Gustav

On 1500 UTC 1 September 2008, Hurricane Gustav made landfall over the southern coast of Louisiana. The Mobile Integrated Profiling System (MIPS) and the Mobile Alabama X-band (MAX) radar, which were located about 170 km northeast of the vortex center, observed widespread stratiform and embedded convective rainbands from 1200 to 2200 UTC. A prominent bright band was observed during this period and high rainfall rates up to 54 mm/hr were measured at the ground during passage of the convective rainband.

In order to improve understanding of the vertical variation in microphysics from 1200 to1600 UTC, a period which included both stratiform and some convective precipitation (moderate to heavy precipitation), raindrop size distributions and vertical air motion are retrieved using the 915-MHz profiler spectra. In addition, the vertical and temporal changes in horizontal divergence profiles from the MAX radar data during the period are also examined with an emphasis on properties around the melting layer as well as the lower-levels. The MAX dual-polarimetric measurements with RHI scans are compared for analyzing microphysical and kinematic properties associated with the horizontal divergence and wind profiles.

The retrieved precipitation parameters with vertical air motion accounted for can provide more realistic information on understanding vertical changes of microphysical processes in still air. The vertical characteristics of the precipitation parameters and the Z-R relations averaged in several rain layers, which represent the changes of mean drop sizes and number concentrations, will be presented. The comparison of the retrieved rain rates with those measured from the Parsivel disdrometer will also be shown.