Temporal And Spatial Variation Of Snow Cover Over The Tibetan Plateau And Its Circulation Background

Snow cover is an important component of cryosphere.It can significantly change the characteristics of underlying surface because of its high albedo and low thermal conductivity,and affect the energy balance and water cycle in the climate system.Snow cover over the Tibetan Plateau(TP),which plays as a sensitive indicator of climate change,exerts a profound impact on regional and even global hydrology and climate.Therefore,in the context of climate warming,it is of great theoretical and practical significance to study the temporal and spatial variation and the causes and mechanisms of snow cover over the Tibetan Plateau.MODIS 8-day snow cover extent products and ERA-Interim reanalysis data were employed to study the spatial and temporal variability of the snow cover over the.TP and its relation to large-scale circulation anomaly by climatological statistical diagnosis.The spatial distribution of snow cover over the TP is far from uniformity,with high snow cover fractions(SCF)at the western edge and the southeast part of the TP but scarce snow at the northem part and in the center.Rich snow over the Bayankela mountains in the eastern TP and the Nyenchen Tanglha mountains in the southeastern TP is characterized by large interannual variability.While the snow cover over the Karakoram and its surrounding areas in the western TP is relatively stable even though its high value of SCF.The snow over the TP mainly happens in winter and spring.The annual variation curve of the average snow cover over the TP shows a distribution characteristic of multi peak.In late October to late March,the average snow cover over the TP is with high value of SCF and large interannual fluctuations,indicating that snow cover is active during this period.Snow cover over the entire TP decreased slightly but for those over the Tanggula mountains and along the Himalaya.It's found that the winter SCF is out of phase between the eastern and western part of the TP with respect to the leading mode of empirical orthogonal functions(EOF1).Namely,the positive(negative)anomalies in SCF over the eastern part of the TP are associated,with negative(positive)anomalies in SCF over the western part.This pattern is positively correlated with AO.During the positive AO phase,the East Asian Through weakens,together with intensive Southern Branch Trough.The warm moist flows easily lift to the eastern part of the TP because of intensive Subtropical High over the Western Pacific and result in excessive snowfall.While an anomalous anticyclone with its center to the southwest of the plateau leads to sinking dry air flows over the western part of the TP,wthich is not in favor of snowfall,and the corresponding higher surface temperature also against maintaining the snow cover.During the negative AO phase,the East Asian Through strengthens and so does the East Asian winter monsoon,with dry cold air flows over the eastern part of the TP,leading to less snowfall.On the other hand,an anomalous cyclone centered to the southwest of the plateau makes it easier for the warm moist flows from the Bay of Bengal and Arabian Sea to lift to the western part of the TP and meet the cold air from Siberia,prompting more snowfall over the western part of the TP.