2010年秋、冬季节华北持续性干旱的气候成因分析

Possible Causes of Persistent Drought Event in North China during the Cold Season of 2010

利用1951～2011年中国台站观测的逐日降水、温度和美国NCEP/NCAR再分析月平均资料,本文分析2010年秋、冬季(11月至次年2月)发生在华北地区持续性干旱的大气环流和海温异常特征,并讨论了北极涛动(AO)和LaNia事件对此次干旱事件的影响。分析表明,2010年发生在华北秋、冬季节的持续性干旱是叠加在降水减少气候趋势之上的一次极端干旱事件,但本次极端干旱事件主要成因是受到同期较强的AO负位相和LaNia事件共同的影响。统计发现:AO的负位相有利于乌拉尔山阻塞高压维持和发展,而贝加尔湖上空出现负位势高度异常,导致东亚中高纬度经向环流加强和冷空气向南侵袭。AO负位相可导致贝加尔湖上空气压场偏低并影响冷空气的路径和强度,进而间接地导致华北地区的干冷气候,而同期LaNia的海温异常分布导致西北太平洋副热带高压偏弱偏南,抑制了西太平洋水汽向华北地区输送,从而直接导致该地区的干旱。由于2010年AO负指数和LaNia事件较历史干旱年份表现出较强和长时间持续性,从而导致了锋面位置位于华北以南和华北本次的持续性干旱事件。

Anomalies in the sea surface temperature（SST） and atmospheric circulation that are linked to the drought event in North China during the cold season spanning 2010-2011 are discussed.The possible impacts of the Arctic Oscillation（AO） and La Ni？a are also addressed in the framework of historical analog analysis based on daily station-observed and NCEP/NCAR reanalyzed data sets.The results suggest that the precipitation in North China exhibits a downward trend over the past decades,however,the extreme drought event occurred during the cold season of 2010 has been mainly affected by the negative phase of the AO and the stronger La Ni？a event.Statistical analysis suggests that during the negative phase of the AO,the geopotential height at 500 hPa decreases around Lake Baikal,the Ural blocking high develops,and meridional circulation anomalies prevail over East Asia.Such high-latitude circulation may enhance the cold surge around Lake Baikal and cause it to shift southward,indirectly causing a cold,dry climate in North China.During La Ni？a years,however,the cooling of the SST in the Ni？o3.4 region weakens the western North Pacific subtropical high and directly blocks the southward moisture flux supply.In contrast to historical drought cases,the stronger and persistent negative phases of the AO and the La Ni？a event pushed the cold front much further south,and the two together caused the persistent drought event in North China during the cold season of 2010.