한반도 여름철 강수량 특성 - 태풍, 장마 및 장마 후 강수를 중심으로

Abstract

The Characteristics of Summer Rainfall in Korea

Oh, Wan-Tak Advisor : Prof. Ryu, Chan-Su Ph.D Prof. Chung Hyo-Sang Ph.D Department of Atmospheric Science Graduate School of Chosun University

In order to investigate the characteristics of precipitation at 6 major cities during the summer season, using the 50 year data from 1954 to 2003, we analyzed the synoptic characteristics of each component using the time series and composite chart of typhoon during the Changma and post-Changma period excluding the typhoon effect that cause a secular change in the precipitation during the summer season. The mean precipitation of summer in major 6 cities of Korea is 699 ㎜, which is 51.8% of annual precipitation. 40% of mean precipitation in summer is caused by the Changma front, while 27% is effected by direct and indirect typhoons. 23% is caused by heavy rainfall post-Changma, 10% is caused by the trough from the previous Changma season. The trend of precipitation during the summer and at the post-Changma season in the Korean peninsula show an increase of 20 ㎜ and 40 ㎜ during the period of 10 years. In particular, Mean and standard deviation of precipitation of the post-Changma season show a large value post mid-1990. The recent increasing trend of summer precipitation of the post-Changma season is caused by an increased extreme value by heavy rainfall. The result of synoptic analysis and the lower and upper level height analysis between the rainy and dry years show a positive anomaly in the North-pacific, Okhotsk regions and the Korean peninsula. The trend shows the structure of low level atmosphere which corresponds to the upper level and the structure of pressure system and which closely correlates to the formation and activity of the large scale stationary front. The water vapor which directly correlate to the precipitation concentrate at the lower levels of the atmosphere, and the transportation system of low level vapor is a major variable in determining the summer precipitation. In water vapor analysis, the size of scope on the strong anomaly area didn't strongly affect the amount of precipitation in the Korean peninsula. The subtropical convergence zone induced by the positive anomaly of water vapor field in Asia closely correlates to the Indian monsoon, and the East Asia monsoon and location is highly related to the precipitation of the Korean peninsula. In the synoptic height field analysis of precipitation of the summer season by typhoon, the low level positive anomaly located in the China continent of 25~50˚N and Japan and the North Pacific of 15~45˚N and relatively low height area formed at near the Korean peninsula in rainy years prevent the access of the south pressure system. The precipitation by typhoon increases when a trough develop in Okhotsk, Manchuria, North China, South Siberia, Europe, South China sea and the Philip sea area, and a ridge develops in central Asia and near the south sea of Japan It shows that many variables contribute to the primary factor of increasing the precipitation during the post-Changma period in the Korean peninsula. It is highly correlated to the large quantity of high water vapor field formation by the summer monsoon activity in East-Asia during the summer season. A high water vapor field located in 20～35˚N, 70～150˚E, is long belt formed from Tibet to North Pacific, and is projected to sustain the water vapor transportation system which support large scale water vapor from Korea to the areas along the north pacific high regions. It is highly correlated to high sea surface temperature area formation in the west pacific area near from the Philip sea to Taiwan and southern Japan. Specially, High SST area in near Philip and South China sea is highly correlated to precipitation of summer season in the Korean peninsula. Because of the heat source from ocean up to August which is the second Changma season, the heat source of Changma in Korea, Meiyu in China and Baiu in Japan came from convective activity at the bay of Bengal and Sea of Arabia which corresponds with the discrete of the East China sea and Philip sea convective activity. It is highly correlated to a recent synoptic field change. The mid- and low-level atmosphere was driven by an upper level structure and the water vapor transportation near 35˚N like synoptic analysis was driven by a large-scale low-level circulation. The height field change is a major characteristic of concern in regard to the recent increasing precipitation trend post-Changma. The ascent of height field at continent of China and North-West Pacific and relatively low height field trend is kept near the Korean peninsula. The structure induces the activity of atmospheric motion at a low-mid level and produces the structure which facilitates the south or south-west movement in the Korean peninsula that moves to the northern regions. It is highly correlated to the trend of rain band, that is, subtropical convergence zone that is related to the east Asia monsoon. The rain band caused by the east Asia monsoon is located at the south east coast of China in May and at the sea of South Japan at June. It also affects the Korean peninsula in late June, and south and mid-China, and mid-Korean peninsula at July. The rain band weakens at the continent of China but a monsoon builds up at south China in August. The second Changma tends to start again in mid-August, and the precipitation at this time contribute to increasing the precipitation in late August. The seasonal variation of heat effect from heat source at the Tibetan plateau simultaneously occurs with variation of atmospheric circulation, and correlates to the summer climate in the east Asian region. Because of so much snow distribution area at the Tibetan plateau in spring, this partially induces the weakened high pressure which correlates to extreme low temperatures and rainy phenomena in the Korean peninsula during the summer season. The positive snow distribution deviation at Tibetan plateau in spring delays the Tibetan high development and induces the continued stationary trough developed at the East Asian area. Frequent rain occurs by the upper cold air break in Korea, but the North Pacific high weakens and strengthens the Okhotsk high which tend to bring the low temperature and much rain in East Asia in summer. Concerning the variation of summer heat effect by snow distribution area at the Tibetan plateau, more research is required on the correlation of summer season precipitation and the increasing amount and intensity of precipitation post-Changma in the East Asia area, including Korea which correlates to the increasing trend of temperature in the Korean peninsula in relations to global warming.