Summer Precipitation Features and Atmospheric Circulation Anomaly in Baiyin
Based on the observation data of the summer precipitation in Baiyin from 1956 to 2009, the variation features of summer precipitation in Baiyin were analyzed by using linear trend analysis, maximum entropy spectrum and wavelet analysis, and then the average anomaly field features of the summer atmospheric circulation in wet and dry years in Baiyin were comparably analyzed by NCEP/NCAR reanalysis data. Results indicated that, the spatial distribution of summer precipitation was extremely uneven, more in south and less in north, and the rainfall variability was higher in central parts than in south and north. The summer precipitation presented an overall decreasing trend from north to south during the recent 53 years, especially in the recent 10 years. The precipitation showed an unstable periodic variation about every 3 and 8 years, and was at present in the less precipitation period from both the large and small scale. There were significant differences in the average geopotential height anomaly fields between the wet and dry years in summer in Baiyin. The upper troposphere divergence and middle and lower troposphere convergence intensified in the wet years;while the upper troposphere convergence and middle and lower troposphere divergence intensified in dry years. There was strong ascend motion in the upper troposphere and even the whole atmosphere at the wet years, which helped the formation of precipitation; while in the dry years, the ascend motion in the upper troposphere was weak, and the descend motion in middle troposphere was strong, which had negative impact on the formation of precipitation.
Summer precipitationVariation featuresCirculation anomalyBaiyin city
国家科技期刊平台
NSTL
万方数据
维普
