江门前汛期不同降水时段特征

通过对江门地区1971～2007年3—6月候雨量、日雨量，2003～2007年南海和华南地区低层（850hPa）风场、向外长波辐射（OLR）场和水汽场在南海夏季风爆发前后差异的比较分析，发现：江门前汛期降水由锋面降水和夏季风降水2个时段组成，降水集中期分别为5月第2候和6月第2候。南海夏季风爆发后，江门第1次出现的降水可看作是夏季风降水的开始，南海夏季风的不同爆发类型对江门夏季风降水的开始时间有不同影响。江门前汛期的锋面降水为大尺度抬升凝结降水，而具有热带性质的夏季风降水为对流性降水；由于降水性质的不同，导致两者在降水持续时间、降水形式等方面表现出差异。

Precipitation Characteristics of Different Periods during the Pre-rainy Season in Jiangmen

The changes of daily and pentad precipitation in Jiangmen area from March to June during 1971-2007 and the differences of 850 hPa wind,OLR and 850 hPa moist transportation around the onset of South China Sea Summen Monsoon(SCSSM) are Investigated.The main results are obtained as follow: the pre-rainy season in Jiangmen area is composed of the frontal precipitation period and the summer monsoon precipitation period.The tight precipitation period of the former mainly appears in the 2nd pentad of May,the other in the 2nd pentad of June.After the onset of SCSSM,the first rainfall in Jiangmen area could be regarded as the beginning of the summer monsoon precipitation.Types of the onset of SCSSM have effects on the begin time of the summer monsoon precipitation in Jiangmen area.due to different mechanisms of the frontal precipitation and the summer monsoon precipitation,the duration and pattern of them differ a lot.