Variation Of Seasonal Frozen Soil In East China And Their Association With Monsoon Activity

Using1962-2001monthly soil temperature data, air temperature at observational stations of China, and the EC WMF reanalysis data, first obtaining the depth of0℃isotherm with Lagrange interpolation method which is used to express the frozen soil depth, it is investigated the spatial and temporal variations of the frozen soil depth in East China under the background of global warming and its association with climate change and winter monsoon activity. The results suggest that:(1) In general, the seasonal frozen soil depth in East China is deeper in the north part and shallower in the south part, also thicker in the west part than that in east part, which is associated with the geography and climate characteristics in this regional. Meanwhile, the frozen soil depth exhibts evident regional difference, and the most significant regional is located in the eastern Inner Mongolia and Yellow River downstream, which is correspondence with two predominant braches of cold air flow impacting East China.(2) In the last40years, the frozen soil depth becomes shallower with its south edge retreating northward since1980s under the background of global warming, which indicates a significant degrading trend of the seasonal frozen soil. The results show that, the abrupt changes of frozen soil depth occur in1987, and the depth reduction rate is most severe in the1980s.(3) The frozen soil depth change has much in touch with air temperature, especially the maximum temperature. In addition, there also exhibts evident regional differences, and the closest regional are in North China. It is revealed that the frozen soil depth is not related with northeast China closely, it may be associated with the snow cover in winter. Furthermore, the south edge of the frozen soil depth is familiar with the0℃isotherm of the air temperature.(4) Variations of seasonal frozen soil have close relationship with East Asia winter monsoon. It is revealed that the cold air flow impacting East China will become stronger(weaker) in the strong (weak) winter monsoon years, causing the air temperature lower(higher), which is lead to the frozen soil depth become thicker(thinner), especially the cold air of the eastern road and the northwestern road invading East China. In addition, the south edge of the frozen soil depth experiences a southward (northward) movement, it is more sensitive to the anomalous activity of East Asia winter monsoon.