我国华南4、5月份降水年代际变化的特征及其与中西太平洋海温的可能关系

利用1951～2005年华南4、5月份降水资料、NOAA海温资料以及NCEP再分析资料,对华南4、5月份降水年代际变化的特征、及其所对应的大尺度环流以及与中西太平洋海温的关系作了分析。结果表明,华南4、5月份降水均在1970年代初期发生显著的年代际转变,从之前的降水偏少转变为降水偏多。华南4月份降水与前一年7～11月份的中西太平洋海温、华南5月份降水与当年2～5月份的中西太平洋海温有显著的负相关。在4、5月份年代际降水偏少(多)时期,前期中西太平洋海温偏暖(冷);同期亚洲大陆南部及非洲大陆的海平面气压显著偏低(高),北太平洋海区海平面气压偏高(低);我国华南上空存在反气旋性(气旋性)环流异常,我国华南地区北边界存在显著的南(北)风异常,造成华南地区北边界异常水汽输出增强(减弱)。同时,我国大陆对流层中上层大气显著偏暖(冷),东亚高空急流显著偏北(南),副热带高压偏弱(强)偏东(西),向华南地区输送的水汽减少(增加),从而在华南地区形成异常的水汽辐散(辐合),最终导致华南地区4、5月份降水的减少(增加)。

Characteristics of the Interdecadal Variability of Precipitation in April and May over South China and Possible Relationship with the Mid-West Pacific SST

The characteristics of interdecadal variability of precipitation in April and May and the associated atmospheric circulation, as well as the relationship with mid-West Pacific Ocean sea surface temperature (SST) on decadal scale over South China are analyzed by using observational station data, NOAA SST data, and NCEP reanalysis data for the period 1951-2005. The results show that both the April and May precipitation over South China exhibit a notable decadal change in the early 1970s, which experienced a notable low to high transition. The variability of April precipitation has a significant negative correlation with the Mid-West Pacific Ocean SST from July to November in the preceding year, and precipitation in May has a remarkable negative correlation with SST in the Mid-West Pacific Ocean from February to May in the same year. In the decadal period of lower (higher) rainfall in April and May, the Mid-West Pacific Ocean SST is warmer (colder) in the previous time period; the sea level pressure is significantly lower (higher) in southern Asian continent and the African continent at the same period, and the North Pacific Ocean sea level pressure is higher (lower); there appears an anomalous anticyclonic (cyclonic) circulation over South China, accompanied by a significant southerly (northerly) wind anomalies in the northern boundary of South China, causing a strengthened (weakened) of the anomalous water vapor output in the northern boundary of South China. Meanwhile, the middle and upper troposphere air temperature in the mainland of China is significantly warmer (colder), the East Asian jet stream is obviously northward (southward), the western Pacific subtropical high is weaker (stronger) and eastward (westward), so the water vapor transport to South China is weakened (enhanced), which emerges an anomalous divergence (convergence) of water vapor over South China, resulting in a decrease ( an increase) of April and May precipitation over South China.