中国东部夏季降水异常与青藏高原冬季积雪的关系

Relation between summer precipitation anomaly in eastern China and winter snow in Tibetan Plateau

基于中国740站月降水、积雪、地温资料和NCEP/NCAR再分析月资料,采用相关分析、合成分析和最大协方差法,研究了1979—2008年青藏高原冬季积雪异常与长江中下游夏季降水的关系及其可能的影响机制。结果表明:(1)在年际时间尺度上,青藏高原中北部12月—翌年1月积雪指数与长江中下游夏季降水呈显著正相关。在年代际时间尺度上,1990s—2000s的高原积雪指数与长江中下游夏季降水具有较好的同位相变化特征。表明高原中北部12月—翌年1月积雪指数对长江中下游夏季降水异常具有较好的指示意义,可作为预测长江中下游夏季降水年际年代变化的依据。(2)高原12月—翌年1月积雪异常偏多,是长江中下游夏季洪涝的一个强信号,12月—翌年1月积雪指数正异常年与长江中下游夏季降水正异常年有很好的一致性。(3)高原冬季积雪异常影响长江中下游夏季降水的可能途径是:高原冬季积雪异常通过影响同期及其后春季地温,再由春季地温以某种方式把异常信号维持到夏季。之后,地温异常又改变了局地地气热量交换,导致周围大气环流异常,从而影响到其下游的降水过程。

Based on the rainfall,snow,ground temperature monthly observation data from 740 stations and NCEP/NCAR reanalysis monthly data from 1979 to 2008,the relationship between winter snow anomaly in Tibetan Plateau （TP） and summer rainfall in the middle and lower reaches of the Yangtze River （MLYR） as well as its possible influencing mechnism are investigated with correlation,composition and maximum covariance analysis methods.The results show as follows：（1） For the interannual time scale,a significant positive correlation exists between snow index during Dec-Jan in the central and northern TP and summer rainfall in the MLYR,whose spatial distribution in Dec-Jan is different.For the interdecadal time scale,snow index from 1900s to 2000s in TP has the in-phase variation characteristics with summer precipitation in the MLYR,Which means snow index in Dec-Jan in the central and northern TP is an important indicator to the summer precipitation anomaly（SPA） and the basis for the interannual variation of summer rainfall in the MLYR.（2） Snow index anomaly（SIA） in Dec-Jan in TP and SPA in the MLYR are in a good consistency,which means the positive SIA in Dec-Jan in the central and northern TP reveals the summer floods in the MLYR quite well but it is poor for the droughts.（3） The possible way,in which SIA in Dec-Jan in the TP affects SPA in the MLYR,is that snow abnormal signal first influences soil surface temperature in subsequent 2-3 months through heat exchange and maintains the effect under the soil in some way until next summer,so as to impacts the weather and climate in downstream of TP.