西南秋季降水及其影响要素的气候变化特征

利用西南片区1960—2009年50个气象站的逐日降水和NCEP/NCAR再分析资料,采用谐波分析、双谐样条插值和相关分析等方法,分析该地区近50a秋季降水及其影响因素的气候变化特征.分析结果表明:西南片区秋季降水量呈现减少的趋势,其中降水的年际变化占主要地位,2009年秋季降水量达到50a以来最小值,是线性减少趋势、年际和年代际变化共同作用的结果;各影响因素在不同层次上的气候变化及其与降水的相关性程度各不相同;西南片区秋季地面气温具有显著的增暖趋势,其序列与降水的相关性不显著;对流层中层气压500hPa的秋季温度没有增暖的趋势,与降水的相关性很好,呈显著的负相关,相关系数达到-0.34;气压600hPa的比湿具有线性减少的趋势,与降水呈正相关性,相关系数为0.30;气压700hPa的水平散度没有线性趋势变化,与降水存在显著的负相关.西南片区2009年秋季降水异常空间型与气压500hPa的温度异常偏高型、气压600hPa的比湿异常偏小型和气压700hPa水平散度异常偏强型的相似系数分别为-0.95,0.85和-0.46.该地区2009年秋季降水异常偏少是热力和动力因素共同作用的结果,但热力因素的影响大于动力因素的影响.

Characteristics of autumn rainfall with climate change and its impact factors in Southwest China

Based on daily precipitation data from 50 meteorological stations in Southwest China(including Yunnan,Guizhou,Guangxi,Sichuan,and Chongqing) from 1960 to 2009 and NCEP/NCAR reanalysis data,harmonics analysis,biharmonic spline interpolation,and correlation methods were used to analyze the characteristics of autumn rainfall with climate change and its impact factors in the study area over the last 50 years.The results show the following: Autumn rainfall in Southwest China is declining,and the inter-annual variation of rainfall is predominant.Rainfall in the autumn of 2009 was the minimum amount for the last 50 years,due to a linear decreasing trend,and inter-annual and inter-decadal variations.The changes of the impact factors due to climate change,and their correlation with rainfall varied with different atmospheric layers.The surface air temperature in autumn in Southwest China showed a significant warming trend,and had an insignificant correlation with rainfall.The autumn temperature had no warming trend in the middle troposphere of 500 hPa,and had a significant negative correlation with rainfall,with a correlation coefficient of-0.34.The specific humidity at 600 hPa had a linearly decreasing trend,and a positive correlation with rainfall,with a correlation coefficient of 0.30.The horizontal divergence at 700 hPa had no linear trend,and a significant negative correlation with rainfall.The coefficients of similarity between the anomalous spatial distribution of autumn rainfall in Southwest China in 2009 and the anomalously high temperature at 500 hPa,the anomalously small specific humidity at 600 hPa,and the anomalously high horizontal divergence at 700 hPa were-0.95,0.85,and-0.46,respectively.The anomalous decrease of autumn rainfall in the study area in 2009 was caused by the coaction of thermodynamic and kinetic factors,of which the thermodynamic factors had more significant effects.