1979-2020年西北地区地表风速的年代际变化特征

Decadal Variation Characteristics of Surface Wind Speed in Northwest China during 1979-2020

基于1979-2020年西北地区173个气象站点10 m风速观测资料和ERA-5再分析资料,揭示了西北地区年、各季节风速的年代际变化特征及2003/2004年年代际变化可能的环流背景。结果表明:1979-2020年趋势分布存在显著的区域差异,风速增大区域主要位于甘肃中部和东部、陕西、新疆西南和东北部分地区,其余站点风速大体减小。呈现减小趋势的站点数明显多于增加趋势的站点数,呈现减小趋势站点平均地表风速大于整个西北平均的风速值,呈现增加趋势的站点的平均地表风速小于整个西北平均的风速值,并且在2004年后明显增大。年平均和各季节第一模态的空间分布与1979-2020年趋势分布相似,时间序列的年代际变化发生在2000年前后。年平均和各季节第二模态除宁夏和陕西南部地区为负异常,其余站点大体均为正异常,其时间序列均发生了两次突变,分别发生在1987/1988年和2003/2004年。1987/1988年的西北地区风速变化成因已有大量研究,本研究重点分析了2003/2004年西北风速年代际变化成因的环流因子。从500 hPa位势高度2004-2020年与1988-2003年的合成差图可知,春季环流场呈现中亚-北欧的经向偶极子模态,夏季和秋季呈现为“丝绸之路”模态,冬季呈现“斯堪的纳维亚”模态,年平均呈现为北极涛动负位相。可见,2003/2004年前后四季和年平均环流背景变化都各有特点,它们如何影响中国西北地表风速2003/2004年的年代际变化的物理过程待于进一步深入研究。

Using the observation data of 10 m surface wind speed at 173 meteorological stations in Northwest China from 1979 to 2020 and the ERA-5 reanalysis data,this study investigated the interdecadal variation characteristics of annual and seasonal surface wind speed in Northwest China and displayed the background circulation changes of interdecadal variation in 2003/2004.There are significant regional differences in the trend distribution of surface wind speed during 1979-2020.The stations of the wind speed with increasing trend were mainly located in central and eastern Gansu,Shaanxi,southwest and northeastern parts of Xinjiang.The others stations generally showed the negative trends of wind speed.The number of the stations with decreasing trends of surface wind speed were obvious larger than that with decreasing trends.The average surface wind speed in the stations with decreasing(increasing)trends were larger(smaller)than that in whole northwest China.The distribution of the annual and four-season leading mode of surface wind speed were generally opposite to the trend distribution from 1979 to 2020.All the PC1s experienced the decadal shift around 2000.The second mode showed positive anomalies over the Ningxia Province and southern Shaanxi Province and negative over others regions.The PC2s both witnessed the decadal shifts in 1987/1988 and 2003/2004.Numerical studies investigated the decadal shift of surface wind speed northwest China in 1987/1988.Therefore,this study focuses on analyzing the possible circulation background of the decadal shift of northwest wind speed in 2003/2004.The composite difference of 500 hPa and 200 hPa geopotential heights between 2004-2020 and 1988-2003 presents the meridional dipole mode of Central Asia-Northern Europe in spring,the"Silk Road Pattern"in summer and autumn,the"Scandinavian"mode in winter,and the negative phase of the Arctic Oscillation in annual field.The circulation changes in four seasons and annual averages have their own characteristics.It needs further studies of the physical process of the influences of these circulation factors on the decadal shift of the surface wind speed in northwest China in 2003/2004.