Study on the seasonal cycle of climate and water cycle around the frontal zone and its modulation in East Asia associated with abnormal weather conditions

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This research project aims to integrate new understandings of the various processes on climate and water cycle systems in East Asia and their variability for the basis of predicting the abnormal weather condition and climate change as responded to global-scale factors, such as global warming, with special attention to the "modulation" of its seasonal cycle. The main findings of this project are as follows.1. Over the continental part of China, the "hot wet land surface", as well as the strong low-level southerly wind in the subtropical high area, plays an important role in the maintenance of the very humid air mass to the south of the Meiyu front and the invasion of moisture toward the northern side of the Meiyu front. In addition, the deficiency of specific humidity from the saturation specific humidity once decreases around the Huaihe River Basin (just to the north of the Changjiang River Basin) just before the mature Meiyu season there, resulting in the enhancement of the humidity g … More radient across the Meiyu front.2. In Kyushu, the western part of the Japan Islands, up to about 20% of the total precipitation in the mature Baiu season there was brought in the warm sector of the Baiu front on the surface weather maps, where the huge moisture flux is passing toward the Baiu front. It is also noted that the precipitation in such situation was generally under the meso-scale rainfall systems characterizing the Baiu heavy rainfalls. On the other hand, although the seasonal mean low-level southerly wind toward the frontal zone around the Japan Islands was not so strong in the Akisame season (autumn rainy season) as in the Baiu, the strong southerly wind frequently appeared also in the Akisame season as the year-to-year variation of monthly mean field or sub-monthly variation. It is also interesting that the climatological precipitation showed a small maximum around the northwestern part of Kyushu around the end of August, just before the onset of the Akisame season in the Japan Islands. The rainfall peak around the end of August was basically associated with the processes in the warm sector of the Akisame front. However, appearance frequency of such years decreased after ~1985. As such, the present study illustrates the importance of the atmospheric processes in the warm sector side of the subtropical front (the Baiu/Akisame front), for understanding the rainfall climate and its variability there.3. Analyses of the summertime precipitation revealed the increasing trend around the Baiu/Meiyu front in Japan and China, and the decreasing trend around Mongolia and Philippines, during the years from 1980 to 2000. Model studies as well as observational analyses showed that the Rossby wave propagation through Siberia or Tibetan Plateau also plays an important role. The dynamical processes on the Okhotsk high near Japan in summer were also re-examined.4. Analyses on the various seasons were also made and clarified the followings, for example. (1) Associated with the increase in appearance frequency of the developed extratropical cyclone around Mongolia where the Siberian high develops in winter, rapid temperature rise occurs in the whole region of the Japan Islands at the beginning of April. (2) Condition in which the typhoons approache the Japan Islands even in May or June is greatly affected by the variation of the subtropical high cell coupled with the seasonal mean fields then. (3) The different seasonal mean basic fields from midsummer or Akisame season was also an importantfactor characterizing the rainfall distribution at the approach of Ty0423 in October, the mid-autumn. By summarizing these results, the post research plan of this project was also discussed. Less