广东省汛期旱涝成因和前期影响因子探讨

FORMATION REASONS OF DROUGHT AND FLOOD IN THE RAIN SEASON OF GUANGDONG AND PRECEDING IMPACT FACTORS

根据广东省86个气象站降水量资料,用正态化Z指数对前、后汛期旱涝等级进行了划分。前汛期旱涝年对比分析表明:西太平洋副高造成的南海地区较强偏南风和较强东亚大槽以及较强南支西风急流(有利于中纬度冷空气南侵)之间的相互作用是影响广东前汛期降水偏多的直接原因。广东前汛期偏旱的主要原因是冷空气偏弱。西太平洋暖池海温变化是这种相互作用的重要影响因子,暖池海温偏高(低),广东前汛期正常偏旱(涝)。前期12～2月西太平洋暖池海温是前汛期旱涝变化的重要强信号之一;预测前汛期旱涝时应特别关注两极极涡的强度变化和中纬度地区位势高度变化。后汛期旱涝年份对比分析表明:亚洲夏季风系统偏强(弱)是造成广东省后汛期偏涝(旱)的最重要因素,登陆广东的热带气旋个数对后汛期降水的影响也比较大。还探讨了后汛期旱涝的预测问题,提出前期5月份北太平洋东部地区500 hPa位势高度距平是预测后汛期旱涝的重要强信号,其位势高度为正距平,则广东后汛期偏旱,负距平则偏涝。南半球中高纬地区大气环流变化通过对印度夏季风的影响从而影响后汛期旱涝的变化。

With the rainfall data in Guangdong, the grades of drought and flood in both first stage (Apr.～June) and second stage (Jul.～Sep.) of rain season in Guangdong have been partitioned with Z-index. The grade series in the first stage have 24 years, 6～8 years and 3～4 years cycle. The grade series in the second stage have a 10-year cycle, which have been found by Morlet wavelet transform. With compariton between drier and wetter years in the first stage, it has been found that the major reason of rainfall more than normal is the interaction between the stronger southerly in South China Sea and deeper East Asia trough and stronger high jet in East Asia. The major reason for less-than-normal rainfall is that cold air is weaker. The SST in warm pool of western Pacific has an important impact on that interaction. The warmer the SST, the less the rainfall will be in Guangdong. In the paper, we also discuss the forecast technology. It suggests that SST in the warm pool may play as a significant signal for forecasting the drought and flood in the first stage. The atmospheric circulation anomalies in the middle and higher latitude of both Hemispheres shall be taken more notice for forecasting the drought and flood. With compariton between drier and wetter years in the second stage, it has been found that the stronger (weaker) Asia summer monsoon system is a most important factor for the wetter (drier) and the number of landing typhoon is also another influencing factor. It suggests that the height anomalies of preceding May at 500 hPa in (40～50 癗,160～140 癢) may play as an significant signal for forecasting the drought and flood in the second stage. The atmospheric circulation anomalies in the middle and higher latitude of Southern Hemisphere can affect the drought and flood through their impact on the Indian summer monsoon.