台湾地区登陆台风降雨结构之雷达观测

Radar Observations of Precipitation Structure of Landfall Typhoons in the Taiwan region

中央气象局全省都卜勒雷达网於2001年建置完成，都卜勒雷达所量测的降雨回波和径向速度数据资料，提供了一个前所未有的机会，进行台湾地区降雨系统内部降雨和运动场结构的研究。本文利用位於瑞芳乡五分山雷达回波资料探讨侵台台风降雨结构的特徵，并以纳莉台风(0116)爲例，分析台风登陆前後降雨分布以及降雨率变化特性。同时利用TRMM卫星降雨雷达和微波成像器资料分析纳莉台风登陆前後眼墙区深对流的发展情形。本文同时提出台风定量降雨预报除了了解其降雨强度(rainfall intensity)特性外，也应该重视降雨壮度(rainfall strength)的特徵，对於侵台台风降雨延时(duration)以及影响范围的估计都有重大意义。

The Doppler weather radar network of Taiwan has been completed in 2001 by Central Weather Bureau. The reflectivity and radial velocity data collected by this network provides an unprecedented opportunity to study the precipitation structure and kinematic motion field of the mesoscale precipitation systems in the Taiwan region. In this study, the reflectivity data observed by Wu-Feng-San radar located at Re-Fang (Northern Taiwan) has been analyzed to reveal the temporal and spatial variations of rainfall structure of typhoon Nan (0116) before and after it made landfall. TRMM PR and TMI data were also used to indicate the occurrence of severe convective activity during the landfall period of Nan. The results showed that in a weakly shear environment, the rainfall distribution of Nan while still far from landmass can be attributed to the influence of translating motion. The maximum rainfall intensity was found to locate at the right front quadrant. As the storm approached the island, possibly due to differential friction and terrain lifting, the maximum rainfall intensity shifted to the rear half of the storm. From the annular mean rainfall rate analysis, it is found the rainfall rates in the inner core (in the radius range of 100 kin) of the storm just before landfall increased more than 50% compared to that 6 hours before landfall. This result indicates that Taiwan topography plays an important role on enhancement of the rainfall just prior to the storm made landfall. From different cases study, it has been shown that different typhoons may possess similar rainfall intensity, however, quite different rainfall strength. This difference is important to the determination of the duration and the possible affected area of the storm and should be emphasized in developing the quantitative precipitation forecasting techniques for landfall typhoons.