Precipitation Characteristics in Wet China
Hiroshi Uyeda
Hydrospheric Atmospheric Research Center, Nagoya University, Nagoya 464-8601, JAPANTEL: +81-52-789-3494. FAX: +81-52-789-3436, e-mail: uyeda@ihas.nagoya-u.ac.jp

Abstract
Heavy rainfalls in East Asia are prominent along the Meiyu/Baiu front. In order to understand theformation and maintenance mechanisms of precipitation systems field experiments have been madealong the Meiyu/Baiu front. Through the studies on precipitation systems over East Asia during theMeiyu/Baiu period, importance of studies on atmospheric boundary layer for the formation andmaintenance of precipitation systems is emphasized. In order to clarify the development ofprecipitation systems along the Meiyu/Baiu front, field experiments in wet and dry region are required.
A brief review is made on the research works on the Meiyu/Baiu frontal precipitations over Chinacontinent, East China Sea and Kyushu Island. Based on discussions of importance of very moist
atmosphere below 1 km in the south of the Meiyu/Baiu front for the enhancement of precipitation
systems, observation sites for a field experiment are proposed.

1. Introduction
Many studies on the Meiyu/Baiu frontal
precipitations have been made in East Asia.
Several recent field experiments as shown in Fig.1
are revealing the characteristics of precipitation ineach region.
For Huaihe River Basin, abundant radar data
was collected in 1998 and 1999 during theintensive observation period (IOP) of the GEWEXAsian Monsoon Experiment/ Huaihe River Basin
Experiment (GAME/HUBEX; Zhao and Takeda,
1998). Fuyang radar (r = 250 km) covered theHuaihe river basin with volume scan reflectivitydata every 10 minutes. Three Doppler radar sets
in 1998 and two Doppler radar sets in 1999 wereplaced within the Fuyang radar range.
With Fuyang radar data in 1998, Geng et al.
(2000) discussed the organization of mesoscaleconvective systems. Data in 1999 is analyzed by
Kanada and Tsuboki (2001). Calibration of
Fuyang radar and Doppler radar is tried by Uyeda(2001) by using precipitation radar on board theTRMM (Tropical Rain Measurement Mission)satellite for quantitative use of ground basedradars.
With Doppler radar data in 1998,
detailed analyses were made on structure anddevelopment processes of precipitation systems(Maesaka et al., 2001; Shusse et al., 2000;
Ttsuboki et al., 2000; and others).
Though Huaihe River Basin is located rather
in the north to observe the frequent occurrence ofthe Meiyu frontal heavy rainfalls, the basin issuitable for the observation of formation of
precipitation systems along the boundary between
dry and wet regions. Convective activity in thisregion would have close relation with the Baiu
front over East China Sea and Kyushu Island.

2. Recent finding on the Meiyu/Baiu fronts
In the GAME/HUBEX, precipitation systems
in the Huaihe River Basin were studied in detailwith Doppler radar data and sounding data.
Significant findings on precipitation systems in1998 are as follows (Maesaka et al., 2000;
Yoshida et al., 2002): a) main convective

precipitation at the northern edge of cloud region
when the low level moist air is invading
northward, b) main convective precipitation at thesouthern edge of cloud region when the low level
dry air is invading southward, and c) diurnal
convective cloud activity is prominent in the southof the Meiyu front. Schematic illustrations for
two types of long lasting precipitation systems areshown in Fig.2.
In the west of Kyushu Island, several field
experiments have been carried out on precipitation
systems of the Baiu. Important role of water
vapor front is proposed by Moteki et al. (2001) for
the development of rain band in the south of theMeiyu/Baiu front over East China Sea.
Orographic effects on the heavy rainfalls in thewest of Kyushu are pointed out by Yoshizaki et al.
(2000) and Kato (1998).

Fig.1

Summarizing the studies on the structures ofprecipitation systems during the Meiyu/Baiu,
characteristic features of linear precipitation
systems mainly composed of warm rain process is
proposed as shown in Fig.3.
Based on the knowledge of precipitation systemsof the Meiyu/Baiu, Moteki et al. (2002) proposed
the origins of the Baiu frontal synoptic and mesoα lows over East China Sea and Kyushu Island
as in the downstream of Yangtze River. Clouddevelopments over the area near Shanghai areemphasized by the analyses on objective analysis
data.
Analyses of GMS-IR over East Asia arerevealing the importance of convective activities
over the China continent and East China Sea forunderstanding the development of mesoαscaleprecipitation systems.

Typical location of the Meiyu front and the Baiu front in the late period.
Year and area of recent field experiments area are shown.

Fig.2

Schematic illustrations for two typical types of long lasting precipitation systems
observed in Huaihe River Basin in 1998 during the IOP of GAME/HUBEX.

Fig.3

Schematic illustration for typical precipitation systems developing in the moist conditionsof low altitude. Moist inflow from south in the lowest altitude and southwesterly flow
below melting layer play important roles for the generation of convective rain clouds.

Fig.4

Schematic illustration of theprecipitation area during theMeiyu/Baiu period. Main
precipitation area is in
between the arid and moist
regions over the HuaiheRiver.
Boundary layer
processes in the arid area aremajor concern.

b)a)

Fig.5

Map of candidate sites for field experiments. Enlarged view of square in a) is shownin b). Circles denote the observation range (r = 250 km) of Fuyang radar andHefei radar (blue dots). White dots and Fuyang are sounding stations. Red dots
are candidate sites for a wind profiler.

3. Future plan
In order to clarify the development processesof precipitation systems from meso-β to meso-

α scale over the China continent, field
experiments over the boundary of wet and dry
regions are important. Because precipitation
area in the middle and latter part of theMeiyu/Baiu period is stagnant in the regions
between wet and dry areas as shown in Fig.4.
For the study of boundary layers over wet and dry
region, the area over the Huaihe River is suitableaccording to the experiences of the HUBEX.
Candidate sites are four sites shown by red points
in Fig.5. They are surrounded by radiosonde
observations and are in the coverage of weather
radar observations. For the detailed structure ofboundary layer and the formation mechanisms of
convective clouds, wind profiler and acoustic
sounder would be essential.

4. Concluding remarks
Synchronous observation on precipitation
systems over Yangtze River and East China Sea
during the Meiyu/Baiu period would contribute tothe improvement of heavy rainfall forecasting andunderstanding of climate changes.

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