近50 a华南盛夏降水的季节内差异及大气环流异常特征分析

基于CRU、CMAP、PREC/L、CN05.1、NCEP/NCAR以及全国160个台站的月降水资料,采用经验正交函数(EOF)分解、依赖于季节的经验正交函数(SEOF)分解、滑动平均、空间相关、回归以及合成分析等多元统计方法研究了近50 a华南盛夏降水异常的基本特征及其季节内差异,并讨论了其大气环流异常。结果表明:(1)盛夏7、8月华南降水异常的空间分布都表现为区域一致性,即整个华南地区都为正(负)异常。(2)华南盛夏降水异常在月季变化的时间尺度上存在着同位相和反位相演变,1963—1993年,华南7、8月降水大致为反相演变,即7月华南全区一致偏涝(旱)而8月一致偏旱(涝);1994—2015年,二者总体表现为同相演变,即7月华南全区降水一致偏涝(旱)时8月亦一致偏涝(旱)。(3)大气遥相关型的变化是同相和反相两种演变模态产生的主要原因,同相期间对流层中层7月表现为欧亚遥相关(EU)和东亚太平洋遥相关(EAP)相互配置,8月表现为类似EU和太平洋北美遥相关(PNA)型;反相期间对流层中层7月表现为类似北美东西遥相关(NAEW)型,8月表现为类似EAP型。(4)西太平洋副热带高压的变化与华南盛夏降水季节内差异密切相关。反相期间7月与8月西太平洋副热带高压的差异主要体现在东西位置变化较大,而同相期间变化不大。

Intraseasonal variation of midsummer precipitation anomaly in South China and its related atmospheric circulation anomalies

Based on monthly mean precipitation data from CRU,CMAP,PREC/L,CN05.1, NCEP/NCAR and 160 meteorological stations in China, the intraseasonal variation of the midsummer precipitation in South China and its related atmospheric circulations in recent 50 years were investigated by using the multi-variables statistic methods, including Empirical Orthogonal Function (EOF) decomposition, Season-Reliant EOF (SEOF), moving average, spatial correlation, regression analysis and composite analysis. Results show that the precipitation anomalies in both July and August exhibit consistent spatial variations. There are evident intraseasonal variations in midsummer precipitation over South China. During 1963-1993, there was an out-of-phase evolution of precipitation anomaly in July and August, which implys that more (less) rain in July almost corresponds to less (more) rain in August. However, there was an in-phase relationship in precipitation between July and August during 1994-2015, which presents more/less rainfall in August is generally accompanied by more/less precipitation in July. Further analysis suggests that the anomalous atmospheric teleconnection patterns play dominant roles in the two intraseasonal modes of the rainfall. For in-phase case, the anomalous circulation of the middle troposphere in July is mainly featured by typical Eurasian (EU) and East Asian/Pacific (EAP) teleconnection patterns, while it is related to the EU and Pacific/North American (PNA) teleconnection patterns in August. For out-of-phase case, the spatial pattern of circulation anomaly is similar to the North American East/West (NAEW) teleconnection pattern in July and the EAP teleconnection pattern in August. Meanwhile, the variation of the Western Pacific Subtropical High (WPSH) in July and August is closely related to the intraseasonal variation. In out-of-phase years, the east-west position of the WPSH changes evidently from July to August, while no significant change has been detected for in-phase years.