华山地区近60 a 6-9月降水特征及环流成因分析

Analysis of precipitation characteristics and causes for its circulation from June to September of recent 60 years in areas around Mount Hua

运用滑动平均、回归分析和Morlet小波分析法,用华山站60 a(1956-2015年)的逐日降水资料,对华山地区降水较多的6-9月的降水进行了不同时间尺度的特征和趋势分析,对可能影响降水的环流因子进行了统计分析.结果表明,华山地区月降水呈单峰分布,降水量、降水日数与最大日降水量的峰值均出现在7月. 6-9月的降水量对年降水量贡献很大,占全年58%以上,其中大雨及以上量级降水出现频次占比超过50%.华山地区降水存在比较明显的周期,年内周期主要表现为在6-9月存在4 d左右的准单周季节内振荡,年降水量在1973-1992年存在5 a左右的显著主周期.影响华山地区6-9月旱涝的环流形势差异较大,在涝年主要表现为高空通常有气流辐散,地面有气流辐合,垂直上升运动更强,西太平洋副热带高压位置更西更北,沿副热带高压西侧到达华山地区的低层水汽条件更好,中低纬度冷空气较弱,冷暖空气在华山地区交汇;旱年形势则大致相反.利用大尺度环流因子定量化指数统计验证发现,对于华山地区6-9月汛期降水影响较大的气候因子主要为北半球副热带高压和西太平洋副热带高压北界及脊、北半球副热带高压强度、印缅槽和北半球极涡中心强度,这些因子与华山汛期降水量的相关系数达到-0.13~0.28,且均通过了0.05的显著性水平检验.

By using statistical methods including moving average, regression analysis and Morlet wavelet analysis etc., the daily precipitation data from the Mount Hua station in the past 60 years(1956-2015)was used to study the characteristics and trends of precipitation from June to September in areas around Mount Hua in different time scales. The circulation factors that might have affected the precipitation were also statistically analyzed. The results showed that the monthly precipitation in areas around Mount Hua was unimodal, and the peaks of precipitation, number of precipitation days and maximum daily precipitation were all in July. The precipitation from June to September contributed the most to the annual precipitation thereof, accounting for more than 58% of the whole year. The proportion of large or above magnitude of precipitation exceeded 50% of the total. There was a relatively obvious cycle of precipitation in those areas. The seasonal cycle was mainly characterized by a quasi-single-week oscillation of about 4 days in the period with more precipitation, while the annual precipitation was mainly in the significant main cycle of about 5 a from 1973 to 1992. The atmospheric circulation affecting the droughts and floods in those areas in the same period was quite different. In the flood years, the main performance was that there was usually wind divergence at high altitudes and wind convergence on the ground, which resulted in the vertical ascending motion being stronger. The position of the western Pacific subtropical high was more to the west and north, producing better conditions in that the lower-level water vapor along the west side of western Pacific subtropical high reached the areas around Mount Hua, while the low and medium latitude cold air was weak. Under this condition, warm and cold air would meet. The situation in the drought years was roughly the opposite to that in flood years. Further analysis by using the large-scale circulation factor quantification index statistical verification showed that the climatic factors having a greater impact on the precipitation in the flood season were mainly the northern boundaries and ridges of northern hemisphere subtropical high and western Pacific subtropical high, India-Burma trough, and the center strength of polar vortex in northern hemisphere. The correlation coefficients between these factors and precipitation of Mount Hua in the flood season reached-0.13 to 0.28, all passing the significance test of 0.05 level.