Relationship Between Land Surface Thermal Anomalies Over The Eurasian Continent And Winter Atmospheric General Circulation Anomalies In Mid-high Latitudes And Possible Mechanisms

Based on ERA40monthly reanalysis data, the features of the land surface thermal anomalies over the mid-high latitudes of the Eurasian Continent during1958-2001were investigated, and the possible linkage between the land surface thermal anomalies and the atmospheric general circulation was further explored. Results show that:(1) The annual variability of surface soil temperature in north of the Lake Baikal is higher than other regions in the mid-high latitude of the Eurasian continent. We performed empirical orthogonal function (EOF) analysis on the surface soil temperature over the mid-high latitude of the Eurasian continent. The first EOF mode is mainly characterized by consistent variation of the land surface thermal conditions over the whole continent, while the second mode shows a north-south dipole with the positive center happens over the higher latitude but negative center appears in the lower latitude.(2) The meridional gradients of the surface soil temperature in the Mongolia and its surrounding regions locate in the south of the Lake Baikal, exhibit significant positive correlation with the zonal flows in the mid-high latitude of the Northern Hemisphere. Increased (decreased) meridional gradient of the surface soil temperature tends to increase (decrease) the meridional gradients of both the surface air temperature and the air temperature in the lower atmosphere. According to thermal wind theory, increased (decreased) meridional temperature gradient will result in the increase (decrease) of the atmospheric baroclinicity. Meanwhile the gradient of low level troposphere temperature, the vertical shear of zonal wind and zonal wind itself will be increased (decreased). Such a process may be associated with the inhomogeneity of the global warming. Larger warming amplitude of the surface soil temperature over the higher latitude than that in the lower latitude of the Eurasian continent is responsible for the evident decrease in the meridional gradient of the surface soil temperature, which may be an important reason for the weakened zonal flows over the mid-high latitude during recent years.(3) The strong persistence in soil thermal anomaly in autumn in high latitudes area has been extended to the winter, resulting in winter thermal anomalies in high latitudes area. The land surface thermal anomalies in winter in high latitudes area enhanced the thermal gradient through the East Asia, according to earlier research, the increasing gradient enhanced westerly circulation. The enhanced westerly circulation blocked the cold air from move southward, resulting in a warmer temperature in southern East Asia, increasing the thermal gradient from north to south, forming a feedback mechanism.