East Asia and Western Pacific METEOROLOGY AND CLIMATE

l.INIRCDUCTICN
Climatological data show that the annual rainfall distribution in
central and eastern China (i.e. along the Yangtze River) possesses a
relative maximum during the period of mid-June to mid-July.
Continuous or intermittent precipitation mixed with frequent
rainshowers and thunderstorms is the characteristic feature in this
rainy season. A similar phenomenon is also observed in Japan and
southeastern China where the rainy season occurs about one half to
one month earlier than that of the Yangtze River Basin. This rainfall
maximum is called "Ivfei-Yu"(plum rain) in China and "Baiu" in Japan.
Anong all the meteorologists in Taiwan, Chi(45) was probably the first
one to study the Taiwan Mei-Yu phenomenon. Regarding the occurrence
time of the Mei-Yu season in Taiwan, results of various
studies(39,59,77) suggested that the Taiwan Mei-Yu period occurs from
mid-May to mid-June (Fig.l). It was also found that the Taiwan Mei-Yu
has a more pronounced interannual variation than that of the Yangtze
River Basin, Due to the topographic effect of the Central Mountain
Range, which oriented in a north-south direction along the island, the
Mei-Yu regime is better defined over the west side than the east side
of the mountain(Fig.2,17).
The positive and negative impacts of the Mei-Yu rainfall have long
been recognized by the meteorological ccntnunity and the general public
in Taiwan. It is a well known fact that winter is a dry season over
Taiwan except the northeastern portion. Therefore, if the spring
rainfall is inadequate then drought will be underway. The rainfall in
the Mei-Yu season provides a most effective way to alleviate the
drought. If the spring rainfall is normal but there is a shortage in
the Mei-Yu rainfall, a serious drought can also be expected. It is
clear that rainfall in the Mbi-Yu season is an important water
resource. On the other hand, the negative aspect of the Mei-Yu cannot
be overlooked. Continuous rain in the Mei-Yu season is a disaster to
agriculture. It is harmful to the rice crop that is ripe for
harvesting in the fvfei-Yu season and is harmful to other agricultural
crops as well. In recent years, the growth of the economy in Taiwan
was tremendous. Therefore, property damages caused by heavy rainfall
and the associated flash flooding in the Mei-Yu season becomes much
more serious than agricultural losses due to the continuous rain. Each
of the heavy rainfall/flash flood events, such as the May 28 case of
1981, June 3 case and June 10 case of 1984, caused U.S. $100-300
millions in damage.
Trie main purpose of this paper is to review the studies of the
Taiwan Mfei-Yu. Studies focussed on the Mei-Yu over mainland China were
not included. Also, research in developing forecast techniques as well
as reviews on operational forecasts were not considered. The first
part of this paper discussed the ciimatological aspects and
interannual variability of the Taiwan Mei-Yu. Studies on the
synopticscale circulation systems as well as heavy rainfall and the
related mesoscale convective systems (MISs) were next reviewed. Then
the Taiwan Area Nfesoscale Experiment(X%EX) was described. Finally,
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