东亚中纬度夏季陆面增暖与土壤湿度异常的联系

Linkage between summer land surface warming in mid-latitude of East Asia and soil moisture anomalies

利用1979—2015年ERA-Interim再分析土壤湿度、云量资料,NCEP/NCAR再分析环流资料和CPC土壤湿度资料,分析了东亚中纬度夏季陆面热力异常的时空分布特征及其与前期春季土壤湿度异常的联系,探讨了前期春季土壤湿度影响东亚中纬度夏季陆面增暖的可能途径。结果表明,东亚中纬度夏季土壤表层温度呈全区一致增暖趋势,其中贝加尔湖及以南地区温度变化最剧烈、增暖最迅速,且1990年代中期前后存在一个明显由冷向暖的年代际转变。进一步分析发现,春、夏季西西伯利亚到贝加尔湖北部地区的土壤湿度与夏季贝加尔湖及以南地区的土壤表层温度在年代际和年际尺度上均存在紧密联系:西西伯利亚到贝加尔湖北部地区土壤湿度异常偏高,通常对应贝加尔湖及南部地区夏季土壤表层温度偏高。西西伯利亚到贝加尔湖北部地区春、夏土壤湿度异常可以引起夏季大气环流异常,从而对东亚夏季中纬度陆面热力异常产生影响:春、夏土壤湿度偏高时,贝加尔湖及其南部地区上空位势高度为正异常,对应为反气旋性异常环流,云量减少,有利于东亚中纬度陆面增暖;反之,则对应为气旋性异常环流,不利于陆面增暖。

Based on the ERA-Interim NCEP/NCAP reanalysis data and CPC soil moisture data during 1979—2015,this paper investigated the temporal and spatial distribution characteristics of land surface heat in mid-latitude of East Asia in summer and the linkage between soil moisture anomalies in early spring and anomalous land surface warming in mid-latitude of East Asia,and discussed the possible mechanisms of the influence of soil moisture in early spring on the land surface heat warming in mid-latitude of East Asia in summer.Results show that there is a significant warming trend of summer land surface in mid-latitude of East Asia with the most rapid and strongest warming happened in the Lake Baikal and its south.Meanwhile,there is an evident interdecadal transition from cold to warm around the middle of 1990s.Further analysis suggests that there are close relationships between spring and summer soil moisture anomalies over regions from the West Siberia to the north of the Lake Baikal and summer soil surface temperature in the Lake Baikal and its south at both interdecadal and interannual scales.Increased spring and summer soil moisture over regions from the West Siberia to the north of the Lake Baikal is usually related to summer land surface warming in the Lake Baikal and its south.The anomalous soil moisture can alter the general circulation anomalies in summer,thus affect the land surface thermal anomalies in mid-latitude of East Asia in summer.Increased spring and summer soil moisture tends to induce positive geopotential height anomalies and anticyclonic anomalous circulation in the Lake Baikal and its south,which can further reduce summer cloud amount over the region and result in significant land surface warming in mid-latitude of East Asia.On the contrary,decreased spring and summer soil moisture usually produces cyclonic anomalous circulation and increases summer cloud amount,which is not conducive to land surface warming over the region.