The Dynamic and Microphysical Processes during the Reorganizing Stage of Typhoon Fanapi(2010) based on the Multiple Doppler synthesis and the Drop Size Distribution Retrieved from Polarimetric radar observation

At 00 UTC, September 19, 2010 typhoon Fanapi made landfall on the east coast of Taiwan and its intensity was immediately weaken due to high Central Mountain Ridge. 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. A mobile X-band dual polarization/Doppler radar, TEAM-R (Taiwan Experimental Atmospheric Mobil Radar) had been deployed near the Chigu S-band Doppler radar, together with Kenting S-band radar, and Magong C-pol radar these four radars provided great opportunity to study this event. A new multi-Doppler radars wind field retrieval method proposed by Liou and Chang(2009) was used to synthesize three dimensional wind field. 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. During the same period, from Chigu S-band single Doppler wind pattern, it is obvious that wind direction changed from north wind to gradually increasing south wind at Chigu as the typhoon center passed southwest of Taiwan Island. At 09UTC, a vortex circulation was found at the lee side of Central Mountain Ridge in the synthesis wind field. The retrieved vortex-like pattern was near the lowest pressure location of surface stations observation. During the re-intensifying period, the other important feature is observed by TEAM-R RHI (range-height indicator) mode, the south wind component intensified from low level to mid and high level in a few hours.. The dual- polarimetric parameters of TEAM-R are used to study the microphysical characteristics of this torrential rain band. Three nearby disdrometers and TEAM-R radar further provide rain drop size distribution (DSD).The preliminary results showed the rather large mass weighted diameter Dm(~2.2 mm) and high concentration Nw (normalized intercept of Gamma distribution ~10**4 mm-1m-3) during the heaviest rain period. For the first time in Taiwan, four radar systems had chance to observe the structure change and study the influence of the topography during the reorganizing stage. The blocking of the Central Mountain Ridge may play an important role of the initiation of the tangential wind component. The stronger convection of the spiral band was further enhanced by the up-slope forcing. Subsequently, the typhoon circulation was also strengthen and re-organized.