凉山州夏季旱涝急转及典型年份大气环流特征研究

摘要：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。

Study on the sharp turn of drought and flood in summer and atmospheric circulation characteristics in typical years in Liangshan Prefecture

Abstract: Based on the monthly precipitation data of 17 stations in Liangshan Prefecture from June to September from 1961 to 2020 and NCEP/NCAR reanalysis monthly average grid data, the long-period drought-flood sharp turn index (LDFAI) in Liangshan Prefecture in summer was defined, and the atmospheric circulation characteristics in typical years of drought-flood sharp turn were analyzed. The results show that: from 1961 to 1970, LDFAI is obviously a high value year, and the number of years from drought to waterlogging is more than that from waterlogging to drought, and the intensity of drought to waterlogging is strong; From 2001 to 2010, it was an obvious low-value year, with less drought-to-flood than the drought-to-drought year, with a strong degree of drought and flood in the early stage and a weak degree of drought and flood in the later stage. During the flood period, the westerly belt in the high altitude is weak, the trough ridges in the middle and high latitudes are more obvious, and the meridional movement is strong, which is beneficial to the cold air going south. 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 multi-short-waves and low troughs in the plateau affects Liangshan Prefecture. The subtropical high is in a moderate position, and the west ridge point is located near 25°N and 120°E, which is beneficial to the water vapor transportation from the Bay of Bengal and the South China Sea to Liangshan Prefecture. The water vapor The early period of drought-to-flood year in Liangshan Prefecture is stronger than that of flood-to-drought year, and the water vapor convergence is weak, so it is not easy to produce.