关键词: 黄土高原, 春季透雨, 变化特征, 高空环流, 相关分析

Abstract: Data of saturating rain date during 1971-2000 from 67 metrological stations in loess plateau of Gansu and south-middle part of Ningxia, and data of American NCEP/NCAR upper air and OLR information were used to analyzed the spatial-temporal characters of the first saturating rain date in spring by method of EOF and REOF. Especially, the characters of upper air circulation and OLR in typical year with early or late saturating rain date were analyzed. Results showed that the average saturating rain date in the north of study region is in the last ten days of May, and the date in the south is in the middle ten days of April; the date in 1970s was later, in 1980s was earlier and in 1990s was later. In typical year with early saturating rain date, the 500 hPa average height anomaly in April appeared positive in east and negative in west; the average flow fields of 500 hPa and 700 hPa converged on Qinghai-Xizang plateau and in the west of China; the centers of 500 hPa and 700 hPa average humidity positive anomaly situated in the northwest of China; the average OLR negative anomaly distributed along E-W direction in mid-latitude and the center appeared in the east of Qinghai-Xizang plateau. In typical year with late saturating rain date, the 500 hPa average height anomaly in April appeared positive in west and negative in east; the average flow fields of 500 hPa and 700 hPa were predominated by west-leaned air on Qinghai-Xizang plateau; the centers of 500 hPa and 700 hPa average humidity positive anomaly situated in the south of China, about 10 latitude from the place of that in the year with early saturating rain date; the average OLR negative anomaly decreased distinctively.

Key words: Loess plateau, spring saturating rain, variation character, upper air circulation, correlation analysis