南海夏季风爆发前后华南前汛期降水日变化对比分析

利用华南地区248个国家级地面气象站逐小时降水数据和14个探空站数据，分析了2003—2016年4—6月华南前汛期降水日变化特征。据南海夏季风爆发时间，将降水分为爆发前后两个时段。华南地区主要存在两条大雨带，一个位于云贵高原至南岭山脉以南，另一个位于广东沿海地区。偏北雨带集中发生在后半夜至清晨时段，偏南雨带集中发生在中午至下午时段。南海夏季风爆发前后，降水量不存在明显相关性，相关系数较大时次位于中午至下午时段。前后期年降水标准差在0.5附近，变化幅度明显时段主要集中于凌晨至清晨。午后出现3 h多年降水量变化幅度最大值，最小时段为中午12时。降水量、降水频率和降水强度的经向分布特征明显且相似:降水量和降水频率在112 °E附近出现日变化转折，以西多出现不稳定夜雨，以东白天降水波动较大。在南海夏季风爆发前，降水特征主要表现为西部高频、南部高强，在清晨更多作用于对暴雨系统的增长；季风爆发后则表现为西北-东南南的高频率高强度降水形态，在傍晚更多作用于增加降水发生频率。 

A COMPARATIVE STUDY OF THE DIURNAL VARIATIONS OF ANNUALLY FIRST RAINY SEASON RAINFALL IN SOUTH CHINA BEFORE AND AFTER THE ONSET OF THE SOUTH CHINA SEA SUMMER MONSOON

In this paper, national hourly precipitation data set from 248 stations in southern China and L-band data extracted from 14 stations were selected to analyze the diurnal variation of annually first rainy season (AFRS) rainfall from April to June in 2003—2016. Based on the onset pentad of South China Sea Summer Monsoon, the AFRS is divided into pre- and post-monsoon-onset periods. There are two major rain bands in southern China: one is located at the south of the Yunnan-Guizhou Plateau and the Nanling Mountains, and the other is around the coastal areas of Guangdong. The northern rain belt mainly occurs from midnight to early morning, and the southern rain belt is concentrated from noon to afternoon. There is no obvious correlation of precipitation around the onset of the monsoon. While relatively large correlation is mainly from noon to afternoon, there are even negative correlation coefficients. Standard deviations are mainly around 0.5 and change the most at early morning while the smallest change is at noon. Longitudinal distributions of rainfall amount, frequency and intensity are similar: 112 °E is the longitude where transition happens. Unstable nighttime rain mostly occurs to its west while fluctuating rain happens to its east. In the pre-monsoon-onset period, the rainfall pattern is of high frequency in the west and of large intensity in the south. The major influence of the monsoon is more clearly shown in the strengthening of the intensity of heavy rain. In the post-monsoon-onset period, however, the rainfall pattern is of west, north-east through southeast, south with high frequency and intensity. The monsoon mostly plays a role in increasing the frequency.