凉山州夏季旱涝急转及典型年份大气环流特征研究

Study on the Sharp Turn of Drought and Flood in Summer and AtmosphericCirculation Characteristics in Typical Years in Liangshan Prefecture

利用1961—2020年凉山州17个站点6—9月的逐月降水资料和NCEP/NCAR再分析月平均格点数据,定义了凉山州夏季长周期旱涝急转指数(LDFAI),并对旱涝急转典型年份的大气环流特征进行分析。结果表明:1961—1970年为明显的LDFAI高值年,旱转涝年多于涝转旱年,且旱转涝强度较强;2001—2010年为明显低值年,旱转涝年少于涝转旱年,前期旱涝急转程度较强,后期旱涝急转程度很弱。涝期,高空西风带强度偏弱,中高纬槽脊更为显著,经向运动较强,有利于冷空气南下,中低纬为多波动纬向环流,凉山州上游短波系统活跃,高原多短波低槽东移影响凉山州,副热带高压位置适中,西脊点位于25°N、120°E附近,有利于孟加拉湾及南海的水汽向凉山州输送,水汽通道条件优于旱期,同时低层辐合、高层辐散的配置更明显,更利于上升运动,旱期则相反。凉山州旱转涝年的前期比涝转旱年的前期下沉运动更强,水汽辐合弱,不易产生降水,而旱转涝年的后期比涝转旱年的后期上升运动更强,水汽辐合强,有利于降水的产生。

Based on the monthly precipitation data of 17 stations in Liangshan Prefecture from June to September from 1961 to 2020 and the monthly average grid data of NCEP/NCAR reanalysis,the long-period drought and flood abrupt change index(LDFAI)in Liangshan Prefecture in summer was defined,and the atmospheric circulation characteristics in typical years of drought and flood abrupt change were analyzed.The results show that from 1961 to 1970,the LDFAI was obviously high,and the years from drought to waterlogging were more than those from waterlogging to drought,and the intensity of drought to waterlogging was stronger.The year from 2001 to 2010 is obviously low-value,and the year from drought to waterlogging is less than that from waterlogging to drought.The degree of drought and waterlogging in the early stage is strong,and the degree of drought and waterlogging in the later stage is very weak.During the waterlogging period,the intensity of the westerly belt in the upper air is weak,and the ridge in the middle and high latitudes is more obvious,and the meridional movement is stronger,which is conducive to the cold air moving southward.The middle and low latitudes are multi-fluctuating zonal circulation,and the short wave system in the upper reaches of Liangshan Prefecture is active.The eastward movement of the plateau multi-short wave trough affects Liangshan Prefecture,and the subtropical high is in a moderate position,and the western ridge point is near 25°N and 120°E,which is beneficial to the transportation of water vapor from the Bay of Bengal and the South China Sea to Liangshan Prefecture,and the water vapor channel conditions are in Liangshan Prefecture,the early period of drought to waterlogging year is stronger than the early period of waterlogging to drought year,and the water vapor convergence is weak,which makes it difficult to produce precipitation,while the late period of drought to waterlogging year is stronger than the late period of waterlogging to drought year,and the water vapor convergence is strong,which is beneficial to the production of precipitation.