Analysis On Characters And Causes Of Spring Precipitation In Shandong Province

By using the monthly averaged NCEP/NCAR reanalysis data of atmospheric circulation and the data of spring precipitation in 81 meteorological stations in Shandong province from 1961 to 1998, spatial and temporal characteristics of spring precipitation are analysed, and the relations between the atmospheric circulation and rainfall patterns are discussed. It is found that the geopotential height above Korea-Japan area is a "key region" which has the most important influence on spring precipitation in Shandong.The spring precipitation is degressive from southeast to northwest of the province. The difference of precipitation between the south and the north is obvious. The maximum of precipitation in the southeast is nearly twice the minimum of precipitation in the northwest. The precipitation tends to increase gradually from March to May. The contributions of each month to the total seasonal precipitation are 17 percent , 36 percent and 47 percent respectively . The: greatest interannual precipitation variability is found in the southeast and the smallest one in the northwest of the province. The basic precipitation pattern is in phase with each part of the whole province. Drought easily occurs in Shandong in spring. There are obvious interannual variations in spring precipitation in Shandong province, and the oscillation period is about 4. 8-6 year.The precipitation data from 81 gauge stations are analyzed by means of EOF. Since the first three principal components can account for 81% of the total variance, the three corresponding fields should be able to represent the main characters of the spring precipitation. They are: synchronized in the whole area of the province (63% of the total variance), out of phase with southeastern part and northwestern part (11% of the total variance), and out of phase with southwestern part and northeastern part (7% of the total variance). Accordingly, four precipitation subdivisionsare put forward: I (south area including Rizhao, Linyi, Zaozhuang and Jining), II ( east area including Yantai, Weihai, Qirgdao and the east of Weifang), III( north area including Heze and Liaocheng) and IV ( north area including Dezhou,Binzhou,Dongying, Jinan,Taian, Laiwu, Zibo and the west of Weifang). The synchronization pattern is the basic one in each month of the season.The relation between the atmospheric circulation and rainfall patterns during spring in Shandong province is discussed. Longitude circulations exist in the SOOhPa height fields in wet. springs and latitude circulations exist in dry springs. The composite: differences of the atmospheric circulation exist in wet springs and dry springs, which appears to be the EU teleconnection pattern of the general circulation. The Korea-Japan area is also in an active center of the pattern, which is a "key region" where the 500hPa height field influences the spring precipitation of Shandong province. The weaker trough in East Asia and the distinctly lowered geopotential height of Ural area are the main causes of the heavy precipitation during spring in Shandong province, and the vapor transfer from gulf of Bengal is favorableness for precipitation during spring in Shandong province.Using the singular value decomposition (SVD) technique, the relationship between 500hPa height fields and spring precipitation in Shandong Province is studied. The result shows that the Korea-Japan area is a "key region" where the 500hPa height field influences the spring precipitation of Shandong province. The atmospheric circulation pattern of Higher in the east and lower in the west causes mucn spring precipitation in Shandong Province, and on the other hand the pattern of higher in the west and lower in the east causes little spring precipitation. The matters of spring precipitation on each month in Shandong province are not entirely homologous, so "key regions" on each month is not. The northeast Japan is the "key region" in which the SOOhPa height fields of the preceding winter influence spring rainfall in the south Shandong Province, hence it can...