一种改进的高原季风指数及其与四川春旱的关系
An Improved Plateau Monsoon Index and Its Relation with Spring Drought of Sichuan Province
中文摘要：
利用1961—2016年四川150个气象站的春旱日数资料和NCEP再分析资料，采用相关分析、小波分析，以及合成分析等方法，通过对Div_PMI的改进定义了一个新的高原季风指数Div_PMI2，并分析了高原冬季风异常造成四川春旱异常的可能原因。结果表明，四川大部地区春旱日数呈弱的减少趋势，但春旱常发区（四川盆地西部和南部及川西南山地）呈显著增加趋势；与几种代表性高原季风指数比较，Div_PMI2能够更好地反映高原冬夏季风的转换时间和相对强弱，56年内该指数冬（夏）季均为正（负）值，没有出现相反的情况，并且与四川平均春旱日数有更高的相关性和更为相似的周期振荡特征；环流分析表明，当高原冬季风偏强时，春季西伯利亚高压偏弱、孟加拉湾和高原高度场偏高、西太平洋副高偏东，导致北方冷空气偏弱、高原低值系统发展受阻、西南暖湿气流不能输送到四川，加之对流层中层被下沉气流所控制，水汽向外辐散，由此导致该地区出现晴朗少雨天气，发生春旱。
中文关键词：
高原季风，四川，春旱
KeyWords：
plateau monsoon, Sichuan, spring drought
Abstract：
By using the data from 150 meteorological stations in Sichuan and the NCEP reanalysis data, and the methods of correlation, wavelet and synthetic analysis, a new plateau monsoon index (Div_PMI2) was constructed by improving the Div_PMI.The possible reasons for the abnormal spring drought caused by the plateau winter monsoon were analyzed. The results showedthat in most areas of Sichuan Province, the number of spring drought days tended to decrease weakly, but the spring drought-proneareas (western and southern Sichuan Basin and mountainous areas in southwestern Sichuan) tended to increase significantly. The Div_PMI2 was always positive (negative) in winter (summer) from 1961 to 2016. Therefore, the new index can better characterize the transition time and relative strength of the plateau monsoon compared to several typical plateau monsoon indices. The Div_PMI2 index has higher correlation and more similar periodic oscillation characteristics with the average spring drought days than other indices in Sichuan province. The analyses of circulation showed that the Siberian high was weakened and the height field in the bay of Bengal and the plateau was positive anomaly when the plateau winter monsoon was strong. As a result, the cold air in the north was weak, the development of low-value system in plateau was hindered, and the southwest warm and humid air flow could not be transported to Sichuan. In addition, the middle troposphere was controlled by subsidence airflow, and water vapor diverged outward, which led to sunny and rainless weather and spring drought in this area.