我国华南3月份降水异常的可能影响因子分析

利用1951～2005年华南地区3月份的降水资料、NOAA海温资料、Ni?o3.4指数和NCEP再分析资料,分析了华南3月份降水异常与同期环流场、全球海温场的关系,从环流和海温的角度揭示了华南3月份降水异常的可能原因。结果表明,当华南3月份降水偏多(少)时,在对流层中低层,北太平洋海区存在气旋(反气旋)性环流异常,西太平洋及南海海面上存在反气旋(气旋)性环流异常,这样的环流异常有利(不利)于东南暖湿气流与北方东部异常冷空气在华南地区形成水汽辐合,导致降水显著增多(减少)。进一步的分析表明,ENSO和北印度洋及南海附近海温是影响华南3月份降水异常的重要外强迫因子,ENSO对华南3月降水异常的影响是通过影响春季西太平洋副热带高压和低层风场异常实现的,而北印度洋及南海附近海温对华南3月降水异常的影响则是通过垂直环流场异常和低层风场以及西太平洋副热带高压异常来实现的。

Analysis of the Possible Factors that Influence March Precipitation Anomalies over South China

The relationships of the March precipitation anomalies over South China with the associated circulation and the global sea surface temperature (SST) field are analyzed by using observations of March rainfall over South China, NOAA SST data,Niño3.4 index, and NCEP reanalysis data for the period 1951-2005. The possible causes of the March precipitation anomalies over South China were revealed from the point of view of the atmospheric circulation and SST field. The results show that when March rainfall over South China is above (below) normal, a cyclonic circulation (an anticyclonic) anomaly exists in the middle-low-level of the troposphere over the North Pacific Ocean, and an anticyclonic (a cyclonic) circulation anomaly appears over the western Pacific Ocean and the South China Sea. These circulation anomalies are favorable (unfavorable) to the southeast warm-moist air flow and the abnormal cold air in the east of northern China which form a water vapor convergence over South China, leading to a significant increase (decrease) of precipitation. Further analysis showed that the El Niño-Southern Oscillation (ENSO) and North Indian Ocean and South China Sea SST are important external factors that influence the March precipitation anomalies over South China. The influence of ENSO on the March precipitation anomalies over South China is through the western Pacific subtropical high and low-level wind field anomalies, and the influence of the North Indian Ocean and South China Sea SST on the March precipitation anomalies over South China is affected by the vertical circulation and low-level wind field anomalies, as well as the abnormal western Pacific subtropical high.