Studv of unusual waether regimes in the summers of 1993 and 1994

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The cause of the unusual and wet summer of 1993 and the unusual hot and dry summer of 1994 are clarified based on the detailed data analysis and the theoretical consideration by using the general circulation model. It is documented that the unusual weather in both summers are considerably affected by the tropical atmosphere-ocean system. In addition, it is confirmed that air temperature shows remarkable decrease due to the appearance of sub-polar jet stream in the lower troposphere over Siberia and the developing of the Blocking High over the Sea of Okhotsk in 1993. It is also found that summer precipitation increase as the result that the Baiu Front. is intensified by the large north-south temperature gradient around Japan. In 1994, it is clear that the increase of surface temperature is amplified due to the eastward migration of Tibetan High and the local surface dryness. These analytical results in both summers are almost supported by the climatological simulation by using general circulation model. Especially, it is shown that spatial distribution of sea surface temperature in the western tropical Pacific in the two years are slightly different, From the examination by using longer climatic data, it is found that the range of temperature change is large in 1950s-60s and after 1980s. We also obtain the result that the global atmosphere-ocean system affecting summer temperature in Japan is different between before 1970s and after 1980s.