孟加拉湾风暴Mala结构及对云南强降水的影响

基于南海海域西沙永兴岛近56 a逐日降水量和雨日资料，采用Morlet小波分析方法对西沙永兴岛降水量和雨日的演变趋势、周期变化等进行全面分析。结果表明：(1)西沙永兴岛降水量和雨日有明显的季节变化，夏秋季偏高，冬春季偏低。(2)年降水量和雨日的年际变化并不一致，降水量有显著的年际和年代际变化，而雨日在近56 a来则呈现显著的下降趋势。(3)小波分析表明年降水量在22~24 a时间尺度上周期振荡较为明显，而雨日的显著周期振荡主要出现在3~6 a的短时间尺度上。(4)不同季节降水量和雨日的年际变化也不同，春季降水量主要呈上升趋势，而夏季呈下降趋势。秋季和冬季雨日下降显著。春季降水量20世纪90年代以后，在4~6 a的短时间尺度上周期振荡强度较强，而夏季雨日强度最大的周期振荡频率位于8~12 a。

The change of precipitation and rainy days in Xisha Waters of South China

Based on the daily precipitation and rainy days data at Yongxing island, Xisha waters, in this study we analyzed the changing trend and periodicity characteristics using the Morlet wavelet method. The results shows that: (1) There is a significant seasonal variation of precipitation and rainy days, which is larger in summer and autumn, and lower in winter and spring. (2) Variation of precipitation in Xisha Yongxing Island is dissimilar to that of rainy days. That is, there is a significant decadal variability of precipitation, while rainy days showed an obvious downward trend during the past 56 years. (3) Precipitation had an obvious large time scale (22-24 a) periodic oscillation. However, rainy days had obvious mid-short period (less 15 years) of periodic oscillations. (4) Seasonal variation of precipitation and rainy days are also different. Precipitation in spring shows an upward trend, but declines in summer. In addition, rainy days show an obvious decrease trend in autumn and winter. Precipitation in spring had an stronger short time scale (4-6 a) periodic oscillation after the 1990s, while the maximum periodic oscillation frequency of the rainy days in summer appeared in a time scale of 8-12 a.