南支槽对四川地区降水影响的定量分析

Quantitative Analysis of Influence of South Branch Trough on Precipitation in Sichuan Area

对1981—2017年NCEP/NCAR逐日再分析资料采用客观方法识别南支槽活动,并结合四川地区156个国家观测站的逐日降水资料,统计分析了南支槽的时空分布特征及其对四川地区降水的影响。结果表明:①南支槽平均每年出现47.9次,月分布呈双峰型,1月和5月出现频次最高;②出现最多的区域为孟加拉湾以北、青藏高原南侧的90°E附近,22°～24°N地区;③11月至次年1月为南支槽的增强期,南支槽强度大致上随着经度的增加而减小,但在86°E和96°E附近为增强区;④南支槽活动同期,约73.97%的对应时段四川地区有降水过程,降水频率大值区主要位于盆地西南部和南部;⑤南支槽位置偏西时四川地区更容易出现降水过程,但呈现出较强降水过程对应的南支槽强度较弱的现象。

An objective method is used to identify the Southern Branch Trough(SBT)activity by means of the NCEP/NCAR daily reanalysis dataset from 1981 to 2017.Based on the daily SBT activity and the precipitation data from 156 national observation stations in Sichuan,the temporal and spatial distribution characteristics of SBT and its impact on Sichuan precipitation are investigated.The results show that SBT appears 47.9 times per year and the monthly distribution is bimodal,with the highest frequencies occurring in January and May.The most frequent activitive area is around 90°E and 22°to 24°N,to the south of the Qinghai-Xizang Plateau and north of the Bay of Bengal.SBT usually enhances from November to January.The intensity of SBT generally decreases with increasing longitude,but there are enhanced areas near 86°E and 96°E.About 73.97%of SBT activities will produce precipitation processes in Sichuan,with the high frequency areas located in the southeast and south parts of the basin.When the South Branch is westward,Sichuan is more prone to precipitation.However,precipitation processes with weaker SBT intensity are generally heavier.