Influence Of Eurasian Snow Variability On Climate Change In East Asia

First,the relationships between spring Eurasian snowmelt and East Asian summermonsoon(EASM)dominant mode as well as February-April Eurasian snow anomalies andMay-June rainfall in China of2010had been investigated by using EOF,SVD and linearregression analysis,based on the datasets of snow water equivalent(SWE),snow cover,andsnow depth,stations precipitation observations and atmospheric circulation variables in theNCEP/NCAR reanalysis.Then,based on the statistical linkage,this study simulated the impact of anomalous snowpattern on rainfall in South China,the snow albedo and hydrological effects on the precipitationin China,and the transient atmospheric circulation response to Eurasian snow anomalies byusing CAM3.1. The major conclusions are as follows:(1)The leading EOF mode of spring Eurasian snowmelt showeddecadalvariation,which has good agreement with the EASM interdecadal transition as well as Chinese summerrainfall. The second mode of the snowmelt variability is correlated positively to the EASMvariability as well. When the snowmelt of East Siberian and near Balkhash Lake becomes morein spring,the East Asian tends to appear "negative-positive-negative" meridional wave trainstructure from high latitudes to low latitudes in the summer. Whereas snowmelt becomes less,the conditions favor opposite situation. It may be due to the positive feedback betweenabnormal snow and the atmospheric thickness anomalies in the same areas over the sameperiod,which promotes two high-pressure. Subsequently,the Balkhash Lake high pressuredevelops eastward and part of the East Siberian high pressure moves to low-latitude. As aresult,atmospheric circulations in East Asian formed meridional wave train structure insummer,which may lead to an anomalous change in East Asian summer weather and climate.(2)ThesecondSVDmodeproperlyrepresentsthetimeandspacecharacteristicsofsnowcover and rainfall in2010,whether by using of snow cover or snow depth. Excessive snowcover in Europe,eastern Tibetan plateau and East Asia tend to be associated with increasedprecipitation in South China and decreased precipitation in Central China. Whereas snow coverbecomes less,the conditions favor opposite situation. When less snow depth in Eurasian north of60°N and excessive snow depth in the areas south of60°N,corresponding increased rainfallin South China,whereas decreased in East China,Central China,and Southwest China. Tworesults are not contradictory,that both showed a positive correlation between snow Snow coverin western and eastern Eurasian and succeeding precipitation in South China.(3)The result of numerical experiment consists with thestatistical linkage. The physicalmechanism between Eurasian snow anomalies and rainfall in China is due to the albedo andhydrology action of snow,changing the thermal condition,which can modify the atmosphericgeneral circulation and result in the abnormal rainfall of South China. Eurasian snow anomaliesmay be a major factor which forces late-spring and early-summer rainstorm in South China of2010.(4)The results of numerical experiments indicate that both these effects could haveimpacts on the South China rainfall. However,there are great differences in amplitudes andranges of abnormities induced by those three simulations. The magnitude of abnormities causedby the snow albedo effect is larger than that by the hydrological effect. When those two effectswork together,the result agrees well with observations and the magnitude is the largest.However,the magnitude is not equal to the sum of that caused by the snow albedo andhydrological effects respectively.(5)ThetransientevolutionoftheatmosphericcirculationresponsetoimposedpatternsofEurasian snow anomalies performance as follows:The initial adjustment of the atmosphericcirculation is characterized by an out-of-phase relationship between geopotential heightanomalies in the lower and upper troposphere localized to the vicinity of the forcing. Followingthe initial baroclinic stage of adjustment,the response becomes progressively more barotropicand increases in both spatial extent and magnitude. The equilibrium stage of adjustment isreached in1month,and is characterized by an equivalent barotropic structure accompanying bylocal baroclinic disturbances which can persists for the end of June.