江西汛期典型旱涝年大气低频振荡特征分析

Analysis on Low-frequency Circulation Characteristics of Typical Drought and Flood Years for Jiangxi Flood Season

利用NCEP/NCAR再分析资料以及江西省83个台站逐日降水资料,应用小波分析、Butterworth带通滤波器分析了江西汛期典型旱涝年降水和大气的低频振荡特征。结果表明:1)江西汛期降水涝年、旱年都存在30—60 d的主要周期,涝年低频振荡的强度较旱年更强。2)涝年、旱年低频周期的峰值位相环流存在显著差异:涝年,对流层低层西太平洋副热带地区存在的低频反气旋使西南气流有利于水汽向北输送,在对流层高层中纬度地区存在低频气旋和低频反气旋对,南亚高压脊线位置偏南,对应在江西地区的整个对流层垂直方向上有低频的上升运动;旱年滤波场上形势与涝年有明显的差异。3)典型涝年、旱年低频振荡的传播特征存在差异:旱年最明显振荡中心位置较涝年偏北,且振幅较涝年偏小;涝年、旱年低频涡度都存在西传特征,但旱年西传区域仅局限于115°E以东区域,而涝年则可以西传至100°E附近区域。4)涝年汛期有明显的水汽低频波列活动过程,而旱年未出现明显的水汽低频振荡传播。

Based on the daily NCEP/NCAR reanalysis data and observed daily precipitation from gauge stations during 1960-2015,the low-frequency characteristics of Jiangxi typical drought and flood years are analyzed using Morlet wavelet analysis and Butterworth filter.The study shows that：1）The precipitation in flood season of the flood and drought year has characteristics of 30-60 days low-frequency variation,and the cycle during flood year is more significant than that in drought year.2）From low-frequency circulation characteristics corresponding to peak phases of 30-60 days filter rainfall,there are great differences between drought and flood years in high and low levels.In the low level of flood years,a low-frequency anticyclone over the northwestern Pacific subtropical high regions enhances the water vapor flux significantly.At the same time,there is a low-frequency anticyclone and cyclone in the high level of middle-latitude areas,causing the South Asia high to extend southward with its ridge line,with low-frequency upward in the whole troposphere over the Jiangxi.Corresponding to typical flood years,there are distinct differences in the low-frequency circulation fields of the drought years.3）The are also great differences in propagation characteristics：in drought years,the center of significant oscillation is extended northward with smaller amplitude;westward low-frequency propagation characteristics exist in both flood and drought years,but only limiting in areas east of 115°E in drought years,and limiting in areas east of 100°E in flood years.4）The obvious low-frequency oscillation for moisture trans-port exists in Jiangxi region during flood year while that during drought year is unnoticeable.