The Nonstationary Connection Between The Tibetan Plateau Snow Cover And The Northem Hemisphere Mid-high Latitude Atmospheric Dominant Modes And Its Physical Mechanism

The Tibetan Plateau(TP)is the largest,highest and most complex plateau in the world,whose characteristics of being a cold source in winter and a heat source in summer make it be a crucial role in the modulation of global climate change and severe weather.As the underlying surface of an uplifted plateau on the earth,the Tibetan Plateau Snow Cover(TPSC)can affect the mid-tropospheric atmosphere directly,causing its signal to spread farther and interact with the global atmospheric circulation.In this paper,the interactions and corresponding physical mechanisms between the TPSC and the major modes of mid-high latitude atmospheric circulation in the Northern Hemisphere are discussed by using satellite data.Before studying the TPSC's climatic effects,we first clarified the spatial and temporal distribution characteristics of four seasons of the satellite TPSC data through quantitative statistical analysis,station data comparison and EOF modal analysis.Based on it,we find that the max value centers of the summer TPSC's climatology and inter-annual variability are mainly located in the PamirTienshan(PT)area.Then the possible relationship,its decadal variation and the corresponding physical mechanism between the summer PTSC and the upstream North Atlantic Oscillation(NAO)are discussed.However,in winter,the overall snow cover on the TP is relatively large,and the area with large inter-annual variability is located at the eastern part of the plateau.Therefore,we find the possible association and its decadal variation between the eastern winter TPSC and the downstream Western Pacific teleconnection(WP),and explain the possible physical mechanism.The specific conclusions are as follows:(1)During the four seasons from 1972 to 2007,the max value centers of TPSC's climatology are mainly located at the PT and the eastern TP areas and the former only has a strong inter-annual variability in summer,while the latter has the strongest inter-annual variability in winter.It is found that the spatial-temporal characteristics of the winter SC on the eastern TP and the PTSC are relatively similar by the comparison of the satellite and station data.which confirms the ability of the satellite data to reflect the spatial-temporal distribution of TPSC,and further confirms its spatial-temporal distribution characteristics.The EOF analyses of the TPSC show that the max value centers of the winter/summer TPSC dominate modes are consistent with the centers of the inter-annual variability,and there are significant 2-year and 5-year inter-annual cycles.Besides,the time series of the four season dominate modes all show inter-decadal variation characteristics.(2)The spring NAO has a significant positive correlation with the summer PTSC in the period 1967-1981,but such connection weakens after 1981.According to our analyses,the spring NAO has a decadal variation on its own spatial characteristic around 1981,and its northern center moved westwards significantly.Through the wind-evaporation-SST feedback,the corresponding spring North Atlantic tri-pole SST anomalies(Tri-SSTAs)are changed.Different Tri-SSTAs during the two epochs can both persist into ensuing summer but excite significantly different downstream Rossby wave trains.During the 1967-1981 period,the positive phase NAO corresponds to the anticyclonic anomaly in the East European Plain and East Asia,and the cyclonic anomaly in the Iceland and PT.The latter will lead the low temperature and more precipitation in the PT area,which is conductive to the maintenance of snow cover,and vice versa.In the latter period,such teleconnection can only reach Black SeaCaspian Sea and cannot affect the PTSC.(3)The winter(January)eastern TPSC has a significant negative correlation with the early spring(March)WP in the period 1968-1990,but such connection weakens after 1990.According to our analyses,during the early period,the excessive TPSC corresponds to the upstream anticyclonic anomaly and its northern westerly anomaly is in favor of the stratospheric polar vortex extending to the Atlantic and Eurasia region and the entire layer of anticyclonic anomaly over the polar region of the North America.The southern easterly anomaly of the latter can generate the Northeastern Pacific negative SST anomaly(NEP-SSTA).Such “Ocean bridge”can modulate the above “Atmosphere bridge” through the local cyclonic anomaly and then maintain the TPSC by the anticyclonic anomaly on the northern TP,which triggers Snow coverAtmosphere-Ocean positive feedback so that both of them can be maintained until March.The NEP-SSTA further affects the WP southern center.However,in the latter period,the atmospheric circulation anomalies related to the winter TPSC cannot influence the SST in the key areas.