The characteristics of the Drop Size Distribution revealed from TEAM-R polarimetric radar observation in the stratiform and convective rain of typhoon Fanapi(2010)

At 00 UTC September 19, 2010 typhoon Fanapi made landfall on the east coast of Taiwan, and its intensity was immediately weaken due to the high Central Mountain Range. In the next 12 hours, Fanapi went through a reorganizing process and brought record breaking 600mm rainfall within 7 hours to Gunsan station in southwest Taiwan. From 06 UTC to 12 UTC , a strong convective rain band was slowly gaining its curvature and evolving into a spiral shape. At 12 UTC, an asymmetric eye wall was observed. A mobile X-band dual polarization/Doppler radar, TEAM-R (Taiwan Experimental Atmospheric Mobil Radar) had been deployed near Chi-San stream. With the advantage of the Range Height Indicator (RHI) scanning ability of TEAM-R, many fast scanning vertical cross sections of the strong convective rain band and the reorganizing eye wall were observed. These data sets provided great opportunity to study the microphysical characteristics of this torrential rain case. First, a careful calculation using two nearby disdrometers drop size distribution (DSD) data and T-matrix scattering model verified the accuracy of the polarimetric radar drop size retrieval scheme. The hydrometer classification was applied to identify the particle types in both stratiform and convective regions. The three-dimensional spatial distributions of the Normalized intercept (Nw) and the mass weighted diameter (Dm) of Gamma distribution are retrieved from polarimetric variables ( ZH, KDP and ZDR). Comparing the DSDs from the long-lived strong convective rainband and the newly formed eye wall reveals very intriguing results. The DSD retrieved to show that: 1) In rain band period at 06UTC, there are slightly big diameter and high concentration. 2) In eye wall period at 12UTC, the high reflectivity convection (>35dBZ) is embedded in a stratiform like pattern below 6 km. And there is smaller diameter and high concentration. That means new drops are formed through condensation and early stage of collision and coalescence. The result emphasized again that polarimatric radar do provide a good opportunity to know the characteristics of rain