1961—2012年6—8月内蒙古降水异常及环流特征分析

Abnormal precipitation and its circulation characteristics during June to August from 1961 to 2012 in Inner Mongolia Autonomous Region

利用1961—2012年6—8月内蒙古自治区100个站各月降水量资料,以降水距平百分率划分了单站和全区各月的多、少雨年份,分析6—8月全区多雨和少雨站点百分率变化特征,针对全区夏季各月异常多雨和异常少雨年份,分析了同期北半球欧亚地区大气环流的分布特征。8月降水存在减少趋势,6月和7月则主要表现为阶段性多(少)雨,且少雨年多于多雨年。结果表明:在多雨月份,100 hPa高度场上,欧亚中高纬度呈径向环流分布,极涡较弱。其中,6月为两槽一脊型,内蒙古位于高压脊区前部,7—8月为两脊一槽型,内蒙古位于高压脊区后部;500 hPa高度场上,6月亚洲区主要表现为变形场,内蒙古处于锋生区,或是亚洲中高纬度环流为两脊一槽型,内蒙古处于两高之间的宽广低槽中,7—8月欧亚中高纬度环流主要表现为东高西低,内蒙古自治区位于低压槽区中;850 hPa流场图上内蒙古为气旋性切变区域或为风场辐合区域控制。在少雨月份,100hPa和500 hPa高度场上,欧亚中高纬度呈纬向环流分布,极涡较强,内蒙古位于南亚高压北边的正距平区域;850 hPa流场图上表现为弱的风场特征,无明显的水汽输送。

Based on the monthly precipitation data in 100 weather stations during June to August from 1961 to 2012 in Inner Mongolia, years with abundant and scarce rainfall at a single station and in the study area were classified according to the precipitation anomaly percentage and their characteristics were analyzed. Aiming at the years with abnormally abundant or scarce rainfall, the distribution characteristics of the atmospheric circulation over the north- ern hemisphere in the corresponding period were discussed. The results show that rainfall is in a decreasing trend in August, while it is periodically abundant（scarce） in June and July and years with scarce rainfall are great than that with abundant rainfall. For the years with abundant rainfall, the circulation distribution in the middle and upper lati- tude is radial at 100 hPa height field over the Euope-Asia area,and the polar vortex is weak. The circulation situa- tion is two troughs and one ridge in June and Inner Mongoha is located in the front of high ridge, while it is two ridges and one trough in July and August and Inner Mongolia is located in the back of high ridge. The deformation frontogenesis at 500 hPa in Asia is the main circulation causing the abnormally abundant rainfall in June. Mean- while, the circulation situation in the middle and upper latitude is two ridges and one trough and Inner Mongolia is located in the wide low trough between two ridges in June, while that is high in the east and low in the west and Inner Mongolia is located in the low trough in July and August. It is controlled by cyclonic shear zone or wind convergence zone over Inner Mongolia at 850 hPa contour chart. On the other hand, for years with scarce rainfall, the circulation distribution in the middle and upper latitude is latitudinal, and the polar vortex is strong at 100 hPa and 500 hPa. Inner Mongolia is located in the positive anomaly area of north high pressure in south Asia. Wind field at 850 hPa chart is weak without obvious water vapor transport.