Relationship of Arctic Sea Ice Coverage Anomalies in Summer-Autumn and Extreme Cold Days over the Tibetan Plateau in Autumn-Winter and the Mechanism

In this paper, daily maximum and minimum temperature data (1979-2012) collected at 125 stations in the Tibetan Plateau are used. The observed monthly sea ice concentration field is extracted from the Hadley Centre sea ice data set (1°×1°, 1979-2012). Air temperature, geopotential height, and wind (monthly) fields are obtained from the latest reanalysis of the European Centre for Medium Range Weather Forecasts (ERA-Interim, 1°×1°, 1979-2012). Based on statistical analysis and synthesis analysis, the relationships between the numbers of cold days and cold nights in the Tibetan Plateau region and the key area sea ice fraction in the Arctic are systematically analyzed. The results show that extreme cold days in the Tibetan Plateau in autumn-winter become more frequent in the years when sea ice fraction is low in the key region in summer-autumn. It can be seen that 500 hPa geopotential height in the Arctic is positively correlated that in the Siberia but negatively correlated with that in the Tibetan Plateau. From the polar region to the Tibetan Plateau, there is an obvious flux fluctuation from north to south while the high pressure and anticyclone above the Siberia area become stronger. The Tibetan Plateau is mainly under the control of northerly flows. In the years with low sea ice fraction, the Rossby wave presents a fluctuation pattern from north to south over the Tibetan Plateau and to the north of the Tibetan Plateau, which makes the cold airmass easy to reach the Tibetan Plateau and results in more extreme cold weather days in the region.