1998年长江中下游地区暴雨过程大气低频扰动场分析

摘要

The data of daily precipitation in the mid-lower reaches of the Yangtze River and the reanalysis data of NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research)which have been treated with the physical decomposition on atmospheric variables were used to study the significant char-acteristics of the low-frequency atmospheric disturbances during heavy rainfall events in 1998 based on the methods of Morlet wavelet analysis and Lanczos band-pass filters.The results show that before August it is the precipitation high incidence period,especially for the rainstorms in the mid-lower reaches of the Yangtze River in 1998.There are two kinds of low-frequency oscillations during heavy rainfall events;the 12-24 days low-frequency oscillations (LFO)mainly occur from January to April,and the 30-60 days LFO usually occur from June to August.Heavy rainfall events during January to April in this region are related to the 12-24 days low-frequency disturbed cyclones (or anticyclones)at 850 hPa that move eastward from the Sichuan Basin vicinity in the east side of the Tibetan Plateau,while the heavy rainfall events during May to August are related to the 30-36 days low-frequency disturbed cyclones (or anticyclones)that move westward from the sea surface of the south of the Japan main island.The geopotential height field of the 12-24 days low-frequency disturbances shows a vertical baroclinic structure,and its central axis tilts towards the west,which is different from that of the 30-60 days low-frequency disturbances charac-terized by barotropicity.The strongest signals of 12-24 days low-frequency disturbances that cause the heavy rain-fall from January to April in this region are located around 925-850 hPa and originate from the east side of the Ti-betan Plateau and the mid-high latitudes,respectively.However,the strongest signals of 30-60 days low-frequency disturbances are mostly located around 850-500 hPa and are generated from the eastern and central parts of the Pa-cific Ocean and the near place of the equator,respectively.%利用Morlet小波变换和Lanczos带通滤波对1998年长江中下游地区逐日降水和经大气变量物理分解后的NCEP／NCAR再分析资料进行分析，研究1998年长江流域中下游地区强降水期间大气低频扰动场的显著特征。结果表明：1998年长江中下游地区8月前为降水多发期，更是暴雨频发期，强降水主要存在两种低频振荡，1—4月主要以12—24 d低频振荡为主，6—8月以30—60 d低频振荡为主；850 hPa自青藏高原东部四川盆地附近东移的12—24 d低频扰动气旋或反气旋与1—4月长江中下游地区的强降水有关，而自日本本岛南部海面西移的30—60 d低频扰动气旋或反气旋与长江中下游地区5—8月的强降水有关。12—24 d的低频扰动位势高度场垂直结构具有斜压性，中心轴线向西倾斜；而30—60 d的低频扰动位势高度场垂直结构与其不同，具有正压模态。引发长江中下游地区1—4月强降水的大气低频扰动最强信号位于925—850 hPa附近，分别来自于青藏高原东侧和中高纬地区；而引发5—8月强降水的大气低频扰动最强信号多位于850—500 hPa附近，分别来自太平洋中东部和赤道附近。