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

通过详细的资料分析和大气环流模式的理论考虑，阐明了1993年夏季异常湿润和1994年夏季异常干热的成因。据记载，两个夏季的异常天气都受到热带大气-海洋系统的很大影响。此外，1993年由于西伯利亚对流层低层出现亚极急流和鄂霍次克海阻塞高压的发展，气温显著降低。研究还发现，白云锋面的影响使夏季降水增加。由于日本周围南北温度梯度很大，这一趋势进一步加剧。1994年，由于青藏高压的东移和局地的干旱，地面增温明显放大。用大气环流模式进行的气候模拟基本支持这两个夏季的分析结果。特别是，热带西太平洋海温的空间分布在这两年略有不同，用较长的气候资料检验发现，在20世纪50-60年代和80年代以后，温度变化幅度较大。结果还表明，全球大气-海洋系统对日本夏季气温的影响在20世纪70年代之前和80年代后是不同的。

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.