Progress in understanding of precipitation systems along the Meiyu/Baiu front
during GAME and GAME II
Hiroshi Uyeda , Taro Shinoda and Takeshi Maesaka
HyARC, Nagoya University, 464-8601, Furo-cho, Chikusa Nagoya, Japan.

e-mail: uyeda@rain.hyarc.nagoya-u.ac.jp

Abstract
Intensive field experiments on precipitation systems around the Meiyu front during the GAME/HUBEX and thefollowing observational projects are revealing the characteristics of cloud and precipitation processes over China
continent. The field experiment in the downstream of Yangtze River, after the GAME/HUBEX, revealed asignificant development of precipitation systems in the region and their maintenance over East China. Anotherindependent field experiments over China and East China Sea a re helping to have linked concept on the Meiyu/Baiu
frontal precipitation systems. At the same time, importance of understanding on the development of convective
clouds in the south of the Meiyu/Baiu front is emphasized because the cloud development in a very moist condition is
the significant characteristics of cloud and precipitation of East Asia. Relation between moist land surface and clouddevelopment is becoming one of the important topics in GAME and GAME II. We aim to give a brief summary ofthese recent field experiments on precipitation systems relating to the Meiyu/Baiu front in order to have synthesizedunderstandings on cloud and precipitation over Asian Monsoon regions.
Keyword: Meiyu front, cloud and precipitation systems, diurnal variat ion of convection, field experiments.

1. Introduction
Meiyu (in Chinese) or Baiu (in Japanese) frontal
precipitation is one of the most prominent phenomena in
Asian monsoon. Structure and development processes ofthe precipitation systems around the Meiyu/Baiu front arestudied for better understanding of the land-atmosphereinteractions in continental scale during the GAME and
GAME II. Our main concerns are related to heavy
rainfalls in the Yangtze River Basin because recent studies
related to climate change are paid attention to an increase
trend of annual rainfall amount in the region (Nitta and Hu,
1996; Gong and Ho, 2002). Coherent variations aresuggested between summer rainfall in the middle-lower
reaches of the Yangtze River and in the western part ofJapan. Heavy rainfalls in the Yangtze River Basin in 1991,
1998 and 2003 are within our recollection.
Heavy rainfalls in the Huaihe River Basin in 1991 led
the field experiment of GAME/HUBEX (GEWEX Asian
Monsoon Experiment / Huaihe River Basin Experiment) to
the region (Zhao and Takeda, 1998; Ding, 2001). The
research area of heavy rainfalls was shifted to thedownstream of Yangtze River Basing during GAME II.
At the same time, but with different purposes from the
GAME, intensive field experiments at the east part of theEast China Sea were carried out (Yoshizaki et al., 2002).
During GAME II field experiments on cloud andprecipitations started around the GAME regions. A brief
review of field experiments on cloud and precipitation
systems are given in this paper for discussing the design ofPost GAME.

2. GAME/HUBEX
The first intensive field experiments on the Meiyu

frontal precipitation systems with Doppler radars in the
network of sounding were carried out in 1998 and 1999
over the Huaihe River Basin during the GAME/HUBEX.
Maesaka and Uyeda (2004a,b) showed two types ofprecipitation systems identified with the radar data of IOP
in 1998 (Fig. 1): one without a temperature gradient in thesubtropical air mass and the other with a temperature
gradient as a result of a merger with the cold front.
In the case of no strong temperature gradient on 29
June 1998, two dominant precipitation systems wererecognized. One was the pair made up by the convective
precipitation system on the convergence line near the
ground and the stratiform precipitation system. The otherwas the linear convective precipitation system to the southof the convergence line near the ground. As for the linear
convective precipitation system to the south of theconvergence line, the precipitation generation at 2.0 km inheight and the inflow to the convective cells below 1.5 km
in height were noted as a result of the dual Doppler radar
synthesis. The numerical simulation indicated that thissystem was formed on the eastern edge of a shallow cold
pool. Around this region, the air near the ground wasvery moist (95 % in relative humidity). A weak cold pool
was sufficient to cause the condensation to create asuccessive linear convective precipitation system. A
weak stratiform precipitation system was formed to theeast of the linear convective precipitation and released
large amount of latent heat to contributed for thedevelopment of meso-a -scale precipitation system.
In the case with a temperature gradient on 2 July 1998,
the precipitation band which aligned from west to east wasobserved around the Huaihe River Basin.
This
precipitation band consisted of two parts: one was theconvective precipitation region in the southern edge of theprecipitation band, and the other was the stratiform
precipitation region to the north of the convective
precipitation region. In the southern convective region,
the inflow to the convective cell located in the layer from
2.0 km to 4.0 km ASL and that most of precipitation was
generated around the 0 ℃ layer.

and others are revealing the variety of precip itation
systems around the Meiyu front.
A few field experiments on cloud and precipitation
systems are going on and a few new experiments areplaned in China continent. Continuous observation is
expected for understanding of annual variation of
convection and precipitation.

(a)

(b)

Fig.2:
Schematic illustration of the three-dimensional
structure of the Mesoscale Convective Systems developed in
the downstream of Yangtze River near the coast. (Yamada etal., 2003)
Fig.1:
Conceptual models of the precipitation systems
associated with the Meiyu front (a) in the subtropical air massand (b) on the polar front. The arrows indicate the air flow.
The thick line indicates the shear line which corresponds to the
Meiyu front. The warm and moist air, and cold and dry air
distribute to the south and north of the shear line, respectively.
(Maesaka et al., 2004a,b)

Through the studies in GAME/HUBEX the role of the
moist atmospheric boundary layer in the south of the
Meiyu front is emphasized for understanding thedevelopment of precipitation systems.
Development
process of convective clouds on the moist surface in thesouth of the Meiyu front was studied by Shinoda andUyeda (2002 ).

3. Surrounding regions of GAME/HUBEX
3.1. Downstream of Yangtze River
In order to investigate precipitations in the main
regions of Meiyu, intensive field experiments in thedownstream of Yangtze River were carried out with
Doppler radars and wind profilers in 2001 and 2002 in the
network of sounding (Geng et al., 2004; Yamada et al.,2003). This experiment was cooperative research with
one of the Chinese Key Projects (Ni, 2002). Yamada et al.
(2003) revealed one of the mechanisms on thedevelopment of the meso-a -scale convective system along
the east coast of China: convergence of strong
southwesterly inflow to the Meiyu frontal system and the
low altitude easterly flow from ocean. Geng et al. (2004)

3.2. East part of East China Sea
Intensive field experiments in the east part of East
China Sea and the west part of Kyushu were carried out
from 1998 to 2002 (Yoshizaki et al. 2002) with Doppler
radars, wind profilers, airplane and research vessels on
board radar. One of the interesting results is the findingof the water vapor front (Moteki et al, 2004a,b). They
found a convergence line with the large water vapor
gradient distinct from the Baiu front about 100 km south of
the Baiu front. This gave an approach to reveal the Baiu
frontal precipitation systems over the East China Sea.
Characteristics of precipitation systems along the west
coast of Kyushu Island are studied by Yoshizaki et al.
(2000), Kato et al. (2003) and others.
These recent studies and previous studies in the eastpart of Kyushu Island facing to East China Sea are giving
detailed features on precipitation systems associated with
the Baiu front in the east part of East China Sea. Now weare at the stage to have a unified feature of the Meiyu/Baiu
front from Continent China, East China Sea to the west
part of Japan.
3.3. Out of GAME regions
Observational studies on diurnal variations ofconvective activities in GAME-Tibet and GAME-Tropics
provided good comparison with convective activities
around the Meiyu/Baiu front.
Characteristics ofconvective clouds on Tibetan Plateau during GAME-Tibet
IOP were investigated using Doppler radar data (Uyeda etal., 2001).
In the out of the GAME regions, field experiments
relating to cloud and precipitation systems were made

during GAME and GAME II.
Mori et al. (2004)
examined the diurnal cycle of rainfall and its regionalvariation over Sumatera Island, Indonesia using TropicalRainfall Measuring Mission (TRMM) satellite precipitation
radar (PR) and intensive rawinsonde sounding data.
Islam et al. (2004) studied the diurnal variations of cloud
activity in Bangladesh and north of the Bay of Bengal in2000 using GMS IR data and radar data of Bangladesh
Meteorological Department. Katsumata and Yoneyama(2004) described the characteristics of the observed
internal structure of the internal structure of the ITCZ
precipitating system and related environmental factors in
the western Pacific using C-band Doppler radar data.
Hirose and Nakamura (2002)
depicted features ofseasonal variations of the vertical gradient of rainfall rateover monsoon Asia using TRMM PR data from 1998 to
2000.

maximum area than those over land. Though CCs in thesouthern part were smaller and lived shorter, some of themappeared simultaneously nearby each other and developed
to a huge cluster.
Diurnal variation of surface
temperature calculated from an objective analysis data
provided by Japan Meteorological Agency was consistent
with the diurnal appearance of CC in each domain. Thesefindings would contribute for the improvement offorecasting CCs and associated heavy rainfalls.
By tracking CCs objectively, a generation area of CCs,
which develop to meso-a low and produce heavy rainfalls,
was recognized around the downstream of Yangtze riverand the west pat of East China Sea. The trends shown by
Takeda and Iwasaki (1987) and Iwasaki and Takeda (1993)
are confirmed. The relation between characteristics of
CC in the Meiyu/Baiu front and structure of rainfall
systems is discussed in comparison with Doppler radar
analyses on a few intensive field experiments.

4. Characteristics of cloud clusters
To understand the formation and maintenancemechanism of Meso-scale Convective Systems (MCSs)
around the Meiyu/Baiu front, characteristics of Cloud
Clusters (CCs) which appeared around the front overContinent China and East China Sea during June and Julyof five years (1998-2002) were investigated by using
infrared TBB data of GMS (Geostationary Meteorological
Satellite (Sakamoto and Uyeda, 2002).
Diurnal variation of convective activity is
predominant over land during warm season in East Asia.
The magnitude of the diurnal variation is known to bedifferent over different geography like a plain, mountains,ocean, etc. However few researchers have investigated
the relationship between the appearance characteristics ofCC and the geography. In this study, analysis areas
containing the eastern part of China and East China Sea,
where CC appears frequently along the Meiyu/Baiu front,
were classified into four domains: Yangtze River Basin,
Southeast Mountains, northern part of East China Sea,
southern part of East China Sea. Characteristics of CC
were investigated for each of the four domains andsurrounding areas. An algorithm to detect and identify
CC automatically was developed and 2044 CCs weretracked objectively. Following characteristics of CC
around the Meiyu/Baiu front in the four domains wereclarified.
Diurnal appearance of CC having an afternoon peakon Tibetan Plateau and Yungi Highland and Southeastern
Mountains is clear. In comparison of June and July for
four domains, diurnal appearance of CC having anafternoon peak was predominant in Yangtze River basin in
July, and Southeast Mountains in both June and July.
However, it was not predominant in Yangtze River basin in
June. CCs in Southeast Mountains had shorter lifetimeand smaller maximum area than those in Yangtze River
Basin on average. Over East China Sea, a lot of CCs
appeared around 6 o’clock (local time) in the northern partin both June and July. They had longer lifetime and larger

5. Discussion
Recent field experiments on the precipitation systems
in the Meiyu/Baiu frontal zone acquired data sets toestimate the water mass besides the data for the study on
the structure of the system. The detailed structures of the
Meiyu/Baiu frontal precipitation system, which is a uniquesystem in the mid-latitude Asia, are revealed. However
the unified understanding of the system from the west ofContinent China to Japan is still on the way.
Understanding on the role of the convection in the moist
environment in the south of the Meiyu/Baiu front would
help the understanding on the precipitation systems around
Bangladesh and Bay of Bengal, and over Indo China
Peninsula.
As for the development of convective
precipitation system in the moist environment, treatment ofboundary layer would be very important as shown by
Shinoda and Uyeda (2002). Method to analyze thecharacteristics of cloud clusters with GMS infrared data
would help to reveal the characteristics of precipitation
systems in East Asia in combination with another satellitedata.

6. Summery
Recent field experiments on the Meiyu/Baiu frontal
precipitation systems revealed the development processesof precipitation in the moist environment. Detailed
studies on the systems showed that rapid development of
convective cloud below the melting layer in the south of
the Meiyu/Baiu front plays an important role fordevelopment of meso-ß and meso-a precipitation systems
along the Meiyu/Baiu front. Studies on the annual
variation of precipitation systems along the Meiyu/Baiu
front would help the understanding on monsoon. Further
studies on development of precipitation systems with cloud
resolving model are expected.

References
Ding, Y., Y. Zhang, Q. Ma and G. Hu, 2001: Analysis of thelarge-scale circulation features and synoptic systems in East
Asia during the intensive observation period of
GAME/HUBEX. J. Meteor. Soc. Japan, 79, 277-300.
Geng, B., H. Yamada, K. K. Reddy, H. Uyeda and Y. Fujiyoshi,
2004: An observational study of the development of arainband on a Meiyu front causing heavy rainfall in thedownstream region of the Yangtze river. J. Meteor. Soc.
Japan, 82, 1095-1115.
Gong, D.-Y. and C.-H. Ho, 2002: Shift in the summer rainfall
over the Yangtze River valley in the late 1970s. Geophy. Res.
Lett., 29, 78-1-4.
Hirose, M. and K. Nakamura, 2002: Spatial and seasonalvariation of rain profiles over Asia observed by
spaceborne Precipitation Radar. J. Climate, 15,3443-2458.
Islam, Md. N., T. Hayashi, H. Uyeda, T. Terao, K. Kikuchi, 2004:
Diurnal variations of cloud activity in Bangladesh andnorth of the Bay of Bengal in 2000. Remote Sensing ofEnvironment, 90, 378-388.
Iwasaki, H. and T. Takeda, 1993: Characteristic features on
meso-scale cloud clusters around Japan in the Baiu-seasonfrom 1985 to 1988. Tenki, 40, 161-170. (in Japanese)
Kato, T., M. Yoshizaki, K. Bessho, T. Inoue, Y. Sato and
X-BAIU-01 observatoin group, 2003: Reason fro the failureof the simulation of heavy rainfall during X-BAIU-01:
Importance of a vertical profile of water vapor for numericalsimulatioins. J. Meteor. Soc. Japan, 81, 993-1013.
Katsumata, M. and K. Yoneyama, 2004: Internal structure of
ITCZ mesoscale convective systems and related
environmental factors in the western Pacific: An
observational case study. J. Meter. Soc. Japan, 82,1035-1056.
Maesaka, T., H. Uyeda, T. Kato and M. Yoshizaki, 2004a:
Structure and maintenance process of the precipitation
systems in the Meiyu frontal zone over continental China
during GAME/HUBEX 1998. Part I: Meiyu front in thesubtropical air Mass. J. Meteor. Soc. Japan (submitted)
Maesaka, T., H. Uyeda, T. Kato and M. Yoshizaki, 2004b:
Structure and maintenance process of the precipitation
systems in the Meiyu frontal zone over continental China
during GAME/HUBEX 1998. Part II: Meiyu front mergedwith a coldfront. J. Meteor. Soc. Japan (submitted)
M ori, S., J-I. Hamada, Y. I. Tauhid, and M. D. Yamanaka, 2004:
Diurnal land-sea rainfall peak migration over Sumatera
Island, Indonesia maritime continent, observed by TRMM
satellite and intensive rawinsonde sounding. J. Meter. Soc.
Japan, 82, 2021-2039.
M oteki, Q., H. Uyeda, T. Maesaka, T. Shinoda, M. Yoshizaki and
T. Kato, 2004: Structure and development of merged two

rainbands observed over the East China Sea during
X-BAIU-99 Part I: Meso-ß-scale structure and development
processes. J. Meteor. Soc. Japan, 82, 19-44.
Moteki, Q., H. Uyeda, T. Maesaka, T. Shinoda, M. Yoshizaki and
T. Kato, 2004: Structure and development of merged two
rainbands observed over the East China Sea during
X-BAIU-99 Part II: Meso-a-scale structure and build-up
processes of convergence in the Baiu frontal region. J.
Meteor. Soc. Japan, 82, 45-65.
Nitta, T. and Z.-Z. Hu, 1996: Summer climate variability in China
and its association with 500 hPa height and tropicalconvection. J. Meteor. Soc. Japan, 74. 425-445.
Ni, Y., 2002: Experiment on heavy rainfall in Meiyu front in thestream of the Yangtze River. International Conf. on
Mesoscale Convective Systems and Heavy Rainfall/Snowfall
in East Asia, Tokyo, Japan. 86-88.
Sakamoto, K. and H. Uyeda, 2002: Diurnal convective activities
and cloud clusters in east asia during the Meiyu/Baiu period.
International Conf. on Mesoscale Convective Systems andHeavy Rainfall/Snowfall in East Asia, Tokyo, Japan. 29-33.
Shinoda, T. and H. Uyeda, 2002: Effective factors in thedevelopment of deep convective clouds over the west regionof eastern China during the summer monsoon season. J.
Meteor. Soc. Japan, 80, 1395-1414.
Takeda, T. and H. Iwasaki, 1987: Some characteristics of
meso-scale cloud clusters observed in East Asia between
March and October 1980. J. Meteor. Soc. Japan, 65,
507-513.
Uyeda, H., H. Yamada, J. Horikomi, R. Shirooka, S. Shimizu, L.
Liping, K. Ueno, H. Fujii and T. Koike, 2001:
Characteristics of convective clouds observed by a Doppler
radar at Naqu on Tibetan Plateau during the GAME-Tibet
IOP. J. Meteor. Soc. Japan, 79, 463-474.
Yamada, H., B. Geng, K. K. Reddy, H. Uyeda and Y. Fujiyoshi,
2003: Three-dimensional structure of a mesoscaleconvective system in a Baiu-frontal depression generated in
the downstream region of the Yangtze River. J. Meteor. Soc.
Japan, 81, 1243-1271.
Yoshizaki, M., T. Kato, C. Muroi, H. Eito, S. Hayashi and CREST
Observation Group, 2002: Recent activities of fieldobservations on mesoscale convective systems (MCSs) overEast China Sea and Kyushu in the Baiu Season and over theJapan Sea in winter. International Conf. on Mesoscale
Convective Systems and Heavy Rainfall/Snowfall in East
Asia, Tokyo, Japan. 80-85.
Yoshizaki, M., T. Kato, Y. Tanaka, H. Takayama, Y. Shoji, H.
Seko, K. Arao, K. Manabe and Members of X-BAU-98
Observations, 2000: Analytical and Numerical Study of the
26 June 1998 Orographic Rainband Observed in Western
Kyushu, Japan. J. Meteor. Soc. Japan, 78, 835-856.
Zhao, B. and T. Takeda, 1998: Huaihe River Basin Experiment(GEWEX/HUBEX). Beijing University, 24pp.