Multiscale Diagnosis of the Impact of Low-frequency Oscillation of Summer Eurasian Circulation on Precipitation over Yangtze River Basin,China
The summer precipitation over Yangtze River Basin(YRB)are closely related to the low-frequency oscillations at mid-high latitude over Eurasia,so quantitatively diagnosing the contribution of the circulation anomalies at different scales to precipitation is of great significance in improving the prediction accuracy of droughts and floods.Based on ERA5 daily reanalysis data and CN05.1 daily precipitation data,a circulation index(CI)is defined to classify the summer Eurasian circulation into double-ridge(DR)type and double-trough(DT)type,and the low-frequency oscillation characteristics and the impact of different scales circulation anomalies on precipitation over YRB were investigated.The results show that DR and DT types reflect the different phases of the same low-frequency oscillation cycle of CI,which both have a dominant periodicity of 10-30 days and exert substantial influences on precipitation over YRB.The main results are as follows:① Both two types exhibit a wave train with alternating positive and negative low-frequency height anomalies at 500 hPa over Eurasian mid-high latitude and propagates eastward at the speed of 5°(longitudes)per day;② when DR type reaches the peak phase,the northeastern winds at 850 hPa from the north of low-frequency anticyclone over Okhotsk Sea are conducive to the invasion of dry and cold air from mid-high latitude area to YRB,which converges with the southwestern winds from the west of anticyclone over South China Sea,leading to the transportation of water vapor from South China Sea and Pacific to YRB and the strongest low-frequency precipitation lagging circulation 2 days,which is opposite to the DT type;③ the impact of Eurasian circulation on low-frequency precipitation over YRB is dominated by the background water vapor(greater than 30 days)and low-frequency circulation(10-30 days),followed by the synoptic-scale circulation(less than 10 days)and the background circulation(greater than 30 days),respectively.The contribution of moisture convergence term is about 3 times larger than that of moisture advection term,indicating that the wet advection leads to sufficient moisture conditions,and then precipitation is produced through strong moisture convergence.
anomalous circulationsummer precipitationmultiscale diagnosislow-frequency oscillationpropagation featuremoisture fluxYangtze River Basin
万方数据
维普
