云南1月降水异常的气候成因分析

在云南旱季降水稀少的气候背景下发生的异常旱涝气候事件是短期气候预测面临的难点之一。开展旱季降水异常的气候成因分析,对于提高气候预测准确率具有重要意义。1月是云南隆冬季节的主要时段,降水变化具有明显的偏态分布特征,年际波动非常显著。云南1月降水偏多年与偏少年大气环流有明显差异,500 hPa高度场上有四个区域位势高度与云南1月降水显著相关,中高纬的三个区域分别与斯堪的纳维亚(SCA)型遥相关的三个活动中心对应,低纬阿拉伯海的高度异常与孟加拉湾印缅槽活动有密切联系。当SCA为正(负)位相且阿拉伯海高度负(正)异常时云南1月降水偏少(多)。海洋上两个显著海温影响区域分别位于东南太平洋和北大西洋中西部,海温异常主要通过影响东亚和南亚地区的环流进而对云南1月降水产生影响。利用高度场和海温场的关键区域的数据分别合成高度场和海温场的组合序列,组合序列与云南1月降水有更高的相关性和更好的距平符号对应关系。在高度场和海温场组合序列的散点图上,近80%的年份位于第一和第三象限,这两个区域高度场和海温场的配置对云南1月降水作用一致,落区位置与降水距平符号对应关系很好;其余约20%的年份位于第二和第四象限,高度场和海温场的作用相反,落区位置与降水距平符号对应关系较差。

Analysis on Climatic Causes of Precipitation Anomaly in Yunnan in January

Under the climatic background of rare precipitation in dry season of Yunnan, the prediction of abnormal drought or flood climate events has been one of the most challenging problems in short term climate prediction. It is of great significance to improve the accuracy of climate prediction by analyzing the climatic causes of abnormal precipitation in dry season. In January, the main period of midwinter, the rainfall in Yunnan is characterized by skewness distribution and the interannual change is very significant. The general circulations between more and less rainfall year in Yunnan in January are quite different. There are four significant impact areas in the 500 hPa field which are closely associated with the rainfall in Yunnan in January. Three of them which are located in the middle or high latitude area respectively correspond to the three centers of Scandinavia Teleconnection Pattern, and the last one lies in low latitude Arab Sea whose geopotential height indicates the intensity of trough in Bengal Bay. When the Scandinavia Teleconnection Pattern is in positive (negative) phase and the geopotential height of Arab Sea is negative (positive), the Yunnan rainfall in January is likely to be less (more). There are two significant impact areas of SST, one is located in the southeast Pacific and the other is in middle west area of North Atlantic. Through affecting the circulations in East Asia and South Asia, the SST has an influence on the precipitation in Yunnan in January. By employing the data of significant impact areas of 500 hPa and SST field, the combined sequences of height field and SST field are synthesized respectively. Both combination sequences have higher correlation coefficients and better corresponding rates of anomaly sign with rainfall in Yunnan in January than those of single impact area data. Based on the combined sequences of 500 hPa and SST field in each year from 1961 to 2017, the scatter graph is drawn. Nearly 80% of the total years is located in the first and third quadrants, where the functions of height field and SST field are consistent with rainfall in Yunnan in January. In this case, the location of the falling zone corresponds well to the anomaly sign of rainfall. The remaining 20% years are located in the second and the fourth quadrants, where the height field and the SST field have opposite functions, and the location of the falling zone corresponds poorly to the anomaly sign of precipitation.