Connection Between Spring Land Surface Thermal Anomalies Over West Asia And Early Summer Cold Vortex In Northeast China

The cold vortex index of northeast China is calculated by using the monthly average station temperature data provided by the National Climate Center.North-Eastern cold vortex index's inter annual and decadal change is analyzed using methods such as Mann-Kendall, EOF and calculating coefficient. After calculating correlation coefficient between NECVI and Eurasia land surface thermal factors,significant negative relationship is found. Then the possibly mechanism between NECV and West-Asia thermal factors is analyzed. The results show as follow:(1) The intensity of NECV during 1979-2015 displays a significant decadal fluctuation and an apparent decadal change from a positive-anomaly phase to a negative-anomaly phase around the late 1990s. The circulation background of the first period is in favor of strong intensity of NECV, so does the second one. The same characteristics are found in the land surface thermal factors of the West Asia in spring.The analysis results illustrate that a significantly below-normal (colder) land surface thermal condition corresponds to more intense cold vortex, and for above-normal(warmer) phase the opposite occurs. The possible physical process between them is further to be discussed. Relatively warmer land surface thermal condition is associated with positive geopotential height anomaly that entent from the upper troposphere to the lower level with a stronger wave center. In the spring, the fluctuation transmits to the south of China's northeastern region along the Westerly jet, and in the early summer, it transmits to the northeast of China, finally affects the strength and interdecadal variation of cold vortex in Northeast China(2) The NECV in early summer during 1979-2015 shows a significant inter annual change, which shows a certain degree of cyclical oscillation. The result of correlation coefficient analysis between the inter annual change of NECVI and West-Asia land-surface thermal factors shows that significant negative relationship,which is similar with that of decadal change. The process of land-surface thermal factors impacting NECV in inter-annual time scale is similar with the mechanism of decadal time scale ,but more significant.(3) It shows negative relationship between land-surface thermal factors and precipitation/ soil moisture/ latent heat and positive relationship between thermal factors and sensible heat in spring.On the one hand, because of the decrease of evaporation which is induced by decreased spring precipitation and soil moisture, the latent heat flux decreases,further the land-surface become a heat source causing increased sensible heat flux.On the other hand, the amount of cloud is decreased caused by decrease of soil moisture and evaporation, which increases net solar radiation received by the land and then the thermal factors increase significantly.