REGIONAL AND TEMPORAL VARIATIONS IN PRECIPITATION IN THE EASTERN PART OF THE HIMALAYAS

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The purpose of this study is to clarify the regional characteristics of intraseasonal variation in precipitation in the eastern part of the Himalayas and its relationship with the Indian summer monsoon. The daily precipitation is analyzed mainly in the Bhutan Himalaya and the results are as follows ;1.The difference in precipitation between the southern foothills and the intramontane basin in the Bhutan Himalaya depends mainly on the intensity of daily precipitation, and the difference in the intensity of precipitation is considered to be related to two air circulation systems with a different spatial scale. One is the monsoon circulation system on a synoptic scale and the other is the mountain and valley circulation system on a local scale.2.The precipitation in the Bhutan and Nepal Himalayas is considered to increase (decrease) during the break (active) phase of the Indian summer monsoon in June and July. However, from mid August, the relationship between precipitation in the Bhutan and Nepal Himalayas and the activity of summer monsoon is not clear.3.The cause of heavy rains in 1989 is the cyclones passing near the Bhutan Himalaya around 18th May and 15th June. The cyclone brings relatively widespread heavy rains in the Bhutan Himalaya and, in the intramontane basin, they have much precipitation.Based on above results, it is shown that the relationship between the activity of Indian summer monsoon and the precipitation in the Himalayas changes from July to August. Moreover, it should be careful of the damages caused by the cyclone, especially in the intramontane basin of the Bhutan Himalaya.