Relationship Of Eurasian Snow Depth With Autumn Arctic Sea Ice Anomalies And Its Possible Impact On East Asian Summer Climate

The Arctic sea ice plays a fundamental role in the climate system and has shown significant effect on the climate change.In the context of global warming,the effect of sea ice loss has become one of hot issues in the researches of climate change.However,the effects of sea ice anomaly on the atmospheric circulation and climate condition have not been fully demonstrated yet,the relevant mechanisms have not been formed a relatively consistent understanding.The autumn sea ice exhibits evident year-to-year variation,which exists significant effect on atmospheric temperature and circulation pattern.These changes will affect the terrestrial climate over Eurasia,e.g.,snow depth is vulnerable to these changes.Snow cover is a special and important underlying forcing factor,and anomalous snow cover can usually affect the climate,especially regional climate.Using the snow depth from different datasets,the reliability and accuracy of these datasets are assessed firstly.Then,linkages between changes in Arctic sea ice and Eurasian snow cover anomaly are explored,and physical mechanisms have been also discussed in detail.Finally,the physical processes of snow hydrological effect on East Asia Summer Monsoon and summer precipitation are evaluated.The main results of this study are as follows:(1)Results show that the Glob Snow dataset provided by the Finnish Meteorological Institute(SWEGS)and the Japanese 55-year Reanalysis data(JRA-55)supplied by Japan Meteorological Agency(JMA)can describe the temporal-spatial features of winter snow depth in mid-high latitudes of Eurasia,which are the best consistency with station observations.Two satellite-derived products that cover Eurasia from 1979-2006,i.e.,the snow water equivalent(SWE)data provided by the National Snow and Ice Data Center(NSIDC;SWENSIDC)and the SWEGS,are selected for examination in the present study.The performances of these datasets in representing snowpack conditions are evaluated by comparing the datasets with the observations of snow depth recorded in the Historical Soviet Daily Snow Depth(HSDSD;SDHSDSD)dataset.The results indicate that the SWEGS dataset is more consistent with the SDHSDSD dataset over northern Eurasia than the SWENSIDC dataset.In particular,the SWENSIDC dataset exhibits large discrepancies in northern Europe and western Siberia(NEWS),indicating problems or even errors in the SWENSIDC dataset.Based on three current widely used reanalysis data: the Twentieth Century Reanalysis(NCAR-20 th Century Reanalysis)datasets supplied by U.S.National Oceanic and Atmospheric Administration(NOAA),the ERA-Interim data supplied by the European Centre for mediumrange weather forecasts(ECMWF),and the Japanese 55-year Reanalysis data(JRA-55)supplied by Japan Meteorological Agency(JMA),the applicability for three reanalysis datasets are evaluated using the Historical Soviet Daily Snow Depth.Results show that these three reanalysis datasets can describe the temporal-spatial features of winter snow depth in mid-high latitudes of Eurasia,especially the JRA-55 dataset.The consistency for JRA-55 dataset with station observation(174 stations)is 90%,while for NCAR-20 th Century Reanalysis is 76%,and for ERA-Interim is only 50%.Even for regional scale,JRA-55 exhibits a higher consistency with the stations in Europe and southern Siberia during 1961-1990,and the positive correlation coefficients in the two areas are 0.91 and 0.87,respectively.While the correlation coefficients for NCAR-20 th Century Reanalysis with stations in the two areas are 0.77 and 0.32.(2)With decreasing sea ice in the Barents and Kara Seas(BKS)region,the snow depth exhibits evident regional responses,which are featured by decreased and increased snow depth in the North Eurasia and central Europe,respectively.Further analysis suggests that the Arctic Oscillation(AO)is an important connection between the BKS sea ice and anomalous winter snow depth,which affect both the temperature and the precipitation in winter over the Eurasia.The regional difference mainly comes from significant differences in regional atmospheric general circulation anomalies as well as the various controlling factors affecting the formation of the snowfall.In North Eurasia,water vapor plays a decisive role in the formation of the winter snowfall and further the winter snow depth.Positive(negative)BKS sea ice anomaly generally induces positive(negative)AO pattern,which can enhance(weaken)the zonal wind and increase(decrease)water vapor transportation to the North Eurasia,causing increased(decreased)winter snow depth.In contrast,in Europe,temperature is the dominant factor affecting the formation of the snowfall and the snow depth.Positive(negative)AO pattern,enhances(weakens)the warm moist advection and thus leads to increased(decreased)temperatures in the Europe,consequently resulting in reduced(increased)winter snow depth.(3)Results show that spring snowmelt over Eurasia exists a significant connection with the East Asia Summer Monsoon(EASM),which is also strongly linked to the meridional dipole-distributed summer precipitation in China.It is assumed that soil moisture anomaly induced by the hydrological effect of snowmelt plays a key role connecting the snow cover and the EASM.Corresponding to more snowmelt,soil moisture memory is strengthened and its anomaly persists to summer.The increased soil moisture can continuously cool the atmosphere and lower the temperature.Such a cooling effect leads to a weakened meridional temperature gradient and a decreased baroclinicity between northern Eurasia and the Arctic Ocean.Then,the variation in the atmospheric baroclinicity induced by the nonuniform heating of the land surface exhibits a significant impact on the synoptic eddy.The eddy forcing,similar to the pattern of the geopotential height,plays a positive feedback in intensifying the wave train over northern Eurasia.Consequently,these anomalous circulation patterns ultimately weaken the EASM and influence the summer precipitation over China,with excessive precipitation over the most regions of South China,and deficient precipitation over Northeast China and North China.Conversely,when the snowmelt over Eurasia is less,the East Asian summer monsoon activity is stronger.