Analysis of the Large-Scale Circulation Featues and Synoptic Systems in East Asia During the Intensive Observation Period of GAME/HUBEX

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An analysis of the large-scale Circulation features, major synoptic systems, precipitation, and atmospheric heating fields during the intensive observation period (IOP) of the GAME,/HUBEX identified eight features. l) The beginning and maintenance of the Meiyu season over the Yangtze-Huaihe River Basin in both 1995 and 1999 occurred under the condition of the northward advance and enhancement of the East Asian summer monsoon. 2) The circulation feature~ characterized with two ridges in the region to west of the Baikal lake and the Sea of Okhotsk, respectively, and one trough in between (in the region of the Baikal Lake) in the middle and high latitudes set a stage for the development of Meiyu seasons, Especially, the quasi-stationary Okhotsk blocking high and the upper-level vortex over East China/the Sea of Japan was a couplet of circulation systems under which the Meiyu front over the Yangtze-Huaihe River Basins was stably maintained. 3) The subtropical high in the western Pacific assumed significant westward bnd northward shift before arrival of Meiyu seasons in 1998 and 1999. During the concentrating period of Meiyu precipitation for 1998, its meridional oscillation was closely related to variations of episodes of heavy rainfalls in this region. 4) The low-level easterly aircurrent to the north of the low-level southerly jet played an important role in maintenance of the frontal zone, which is also one of major factors leading to the persistent heavy rainfalls in middle and lowor reaches of the Yangtze River. 5) The formation of the low-level jets is different in the synoptic condition for 1998 and 1999. This difference mainly resulted from the different zonal positions of the subtropical high and activitics of the summer monsoon. 6) There existed a succession of mesoscale disturbances (at les 2 and 3 meso-scale vortices for 1998 and 1999, respectively) along the Meiyu frontal zones. which mostly originated in the eastern flank of the Tibetan plateau and migrated eastward, with vortex centers located to the north of the low-level jet axis and heavy rainfalls in the southeast of the disturbances. 7) Along the Meiyu front, there was a high humidity and lower temperature conditions, while relatively dry and highel temperature conditions existed to south and uorth of the Meiyu front. This kind of sandwich-like temperature and humidity condition is important for the Meiyu maintenance; Zonally, the temperature field was characterized by lower temperature in the west and higher temperature in the east along the Meiyu frontal zone. 8) During the processes of heavy rains in 1998 and 1999, the patterns and the magnitudes of Ql and Q2 are Hearly similar to each other, indicating that the heating over the heavy rain regions was created by the moisture condensation process, due mainly to convective activities. However, it is now not clear how this prosess of energy and water cycle may in turn affect events of heavy rainfalls through feedback effect. The above indications of the largescale circulation features and synoptic systems provide a starting point for further investigation of the energy and water cycle over the Huaihe River Basin.
社団法人日本気象学会の論文
2001-03-25

Analysis of the Large-Scale Circulation Featues and Synoptic Systems in East Asia During the Intensive Observation Period of GAME/HUBEX

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