Possible Linkage Between Spring Extreme Climate Over Fast China And Surface Sensible Heat Flux Over The Eurasian Continent

Based on daily precipitation and temperature observation data provided by National Climate Center, spring extreme precipitation and temperature indices are calculated using RClimDex to show the spatial and temporal distribution of spring extreme precipitation and temperature events over east China. Further, the possible linkage between spring extreme weather over east China and surface sensible heat flux over the Eurasian Continent and the possible influencing path are researched using ERA-20C reanalysis data. Results suggest that:(1) The spatial distribution of spring extreme precipitation over east China shows gradual increase from north to south. The spring extreme precipitation is increasing in the middle and lower reaches of the Yangtze River, while the northeastern region and the northern part of China show a decreasing trend. The spring extreme precipitation increases first and then decreases. The spatial distribution of spring extreme temperature over east China shows that there are more cold nights in northeast and southwest regions and there are more cold days in the Jianghuai region. There are more cold warm nights in the north of Northeastern region and in the southeast of the coastal area. There are more warm days in the southeast of the coastal area. The cold night frequencies and the cold day frequencies show decreasing trend, while the warm night frequencies and the warm day frequencies show increasing trend over east China.(2) When weakened (intensified) spring surface sensible heat flux occurs in the middle latitude of the Eurasian continent (i.e., regions to the west of Lake Balkhash and to the north of Lake Baikal) but intensified (weakened) sensible heat happens in east China, the spring extreme precipitation is usually more (less) over north China but less (more) over south China. Further analysis suggest that weakened sensible heat in the middle latitude but intensified sensible heat in the lower latitude tends to weaken spring subtropical westerly and shift it northward, which benefits enhanced convective and baoclinic instabilities, causing more extreme precipitation in North China, however, decreased baroclinic and convective instabilities together with less extreme precipitation in South China. On the contrary, intensified sensible heat in the middle latitude but weakened sensible heat in the lower latitude tends to produce almost opposite results.(3) The latent heat flux over the Eurasian continent has a significant effect on the spring extreme cold events over east China. When the winter surface sensible heat flux of the regions to the eastern of Lake Baikal and to the north of the Okhotsk Sea is weak, the distribution of surface sea level pressure related with the sensible heat flux anomaly shows the negative phase of NAM, which is conducive to the occurrence of extreme low temperature over east China. The 500hPa geopotential height associated with the thermal anomaly shows deepened East Asian trough,strengthened meridian circulation, and strengthened block high, is conducive to a wide range of cold air south into the eastern region of China providing a large background field for the occurrence of extreme low temperature events .