斗门前后汛期极端降雨趋势及其差异成因分析

Analysis of the Tendency and Difference Causation of Extreme Rains in the Annually First and Second Rainy Seasons of Doumen

利用斗门1979—2016年逐日降雨资料,采用百分位法计算得到斗门前后汛期极端降雨总量和极端降雨强度,运用小波分析对极端降雨强度进行分析,并划分正负异常年对大气环流和海表温度异常进行合成分析,结果表明:近38年来,斗门前后汛期极端降雨总量和强度都有明显的年际变化,前汛期极端降雨总量和强度呈小幅上升趋势,极端降雨强度具有3~5年显著的变化周期;后汛期极端降雨总量维持平稳,强度呈下降趋势,且具有1~3年显著的变化周期。前汛期极端降雨偏多的原因主要是西太平洋副热带高压偏西偏强,珠三角以西为显著的辐合区域,有利于上升运动,北方冷高压加强有利于冷空气南下,南北气流在广东沿海交汇,有利于中尺度对流的生成和活跃,从而导致极端降雨事件的增多。后汛期极端降雨偏多的原因主要是珠三角以西为显著的水汽辐合区域,华北为显著的正高压异常,有利于冷空气堆积南下,西北太平洋为广阔的正海温异常,激发的气旋性环流异常,为该区热带气旋等对流系统的发生发展创造了有利条件,易发生极端降雨事件。

Using the data of daily rainfall of Doumen from 1979 to 2016 and the method of percentile, the total rain amount and rain rate of extreme rains in the annually first and second rainy seasons are determined, the rain rate is analyzed with the wavelet analysis, and a composite analysis of the anomalies of general circulation and sea surface temperature is conducted by classifying positively and negatively anomalous years. The result is shown as follows. Over the 38 years, significant annual variations are observed in the total amount and intensity of extreme rain in both the rainy seasons of Doumen;they showed mildly increasing trends in the annually first rainy season, and the rain rate was marked with significant periods of 3 to 5 years, while in the annually second rainy season, the total amount stayed at a stable level but the intensity tended to drop, changing at significant periods of 1 to 3 years. The main reason for more extreme rain in the annually first rainy season is that a subtropical high in the west Pacific is more to the west and stronger than usual and the area to the west of the Pearl River delta is one of significant convergence, being conducive to ascending motion, and a cold high strengthened in the north, favorable for the southward transportation of cold air to meet northward-going air currents on the coast of Guangdong, making it easy for mesoscale convection to generate and develop to increase the extreme rainfall events. As for the annually second rainy season, the main reason for more extreme rain is that the area west of the Pearl River delta is where water vapor is significantly convergent, the north of China is of significantly positive pressure anomalies which helps the cold air to accumulate and progress southward, the west Pacific is covered with widespread positive sea surface temperature anomalies which trigger cyclonic circulation anomalies. They are favorable conditions for tropical cyclones and other convective systems to generate and develop so that extreme rain events are likely to happen.