presented by
Ben Jong-Dao Jou, Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan. jou@webmail.as.ntu.edu.tw
In this presentation, the precipitation structure of Typhoon Nari (2001) before and after landfall is examined using the reflectivity data collected by NEXRAD in northern Taiwan. The brightness temperature and reflectivity data of TRMM TMI and PR are also used for comparison. The preliminary results show that pronounced precipitation structure changes can be identified during landfall. The contraction of the eye and the associated intensification of precipitation in the inner core region were observed. Significant precipitation enhancement can be traced back to 4-5 hours before the storm made landfall in terms of azimuthal mean reflectivity variations. The final hour enhancement (about 50% increases) before landfall is identified and the effect of complex terrain suggested. The quadrant-mean precipitation structure is also examined. Since the mean vertical shear was weak (<1ms -1) for the whole period, the asymmetrical distribution of precipitation of the storm in the open ocean was consistent with that expected from asymmetric boundary layer flow under a translating storm (Shapiro 1983). The change of the asymmetry during landfall, rotated from right-hand quadrants to upfront quadrants and then to the rear quadrants, can be crudely attributed to the effect of Taiwan topography. From TRMM observations, the detection of very low brightness temperature by 85GHz TMI and significant intensification of radar reflectivity by PR all suggested the existence of severe convective activities during landfall period.
Similar analysis technique has been applied to several other landfalling typhoons in the Taiwan area. Discussions on the characteristics of their precipitation structure changes will be presented during the talk.
Seminar is from
9:30 am to 10:30 am in FL2 Room 1022
on Tuesday, May 3, 2005.
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