East Asia and Western Pacific METEOROLOGY AND CLIMATE

161
seasons sometimes brought great damages in the Taiwan area. On the other hand,
rainfall is also a very important water resource to the island. A raingauge network
consisting of 74 surface weather stations and 126 self- recording raingauges was
set up by Central Weather Bureau in the past few years. Five conventional radars
constitute the radar network(Fig.l). Two S-band radars have provided digital
data since 1985 summer. The other three radars have also provided digital data
since 1988. The first Doppler radar was set up in 1987 by CAA(Civil Aeronautics
Administration) at CKS( Chiang Kai-Shek) airport(Fig.2) in Taiwan area. This
radar has proved its ability to observe precipitaiton systems in northern Taiwan.
A field program of the Taiwan Area Mesoscale Experiment (TAMEX) was
operated from 1 May to 29 June, 1987 in the Taiwan area. Three Doppler radars
were positioned along the west coast of Taiwan, forming a triple Doppler network
(Fig.2). The primary scientific objective of TAMEX is to improve our understanding
of the mesoscale dynamics of the convective systems responsible for heavy precipitation.
In May and June 1986, a field experiment called " TAMEX phase I"
was held in Taiwan area as a testing field program for 1987 TAMEX.
The mesoscale data sets of two cases in TAMEX phase I, 1986 and TAMEX
,1987 were analyzed to study the characteristics of convective system during Mei-
Yu season. Based on the digital radar data, a detailed discussion of the reflectivity
characteristics such as horizontal pattern, vertical structure and movement was
illustrated. In order to understand the kinematics of the convective systems in
TAMEX phase I, the internal motion fields of thise case were also calculated
through the TREC technique. In the TAMEX case study, structural features and
internal motion of one long-lived and slow moving MCS rainband originated from
the Mei-Yu frontal unstable zone which occurred on 25 June 1987 in IOP-13 over
the Taiwan area were investigated .
2. RADAR ESTIMATE AND GUAGE MEASUREMENT
During the TAMEX phase I period, digital radar data with 0.5-hr interval and
rain gauge data with 10 minutes interval in the major events are available. From
May 20 to May 21 1986,a precipitation system was observed across the Taiwan
Strait. It later brought a rainfall accumulation of approxmately 200 mm in two
days in some major cities in the central and northern Taiwan. From 2300 May
20 to 0700 May 21, sixteen reflectivity distributions for every 30 minutes were