Impact Of Nonuniform Land Surface Warming On The Simultaneous Anomalous Extra-tropical Cyclone Activity During Summer Over East Asia

As one of the typical synoptic-scale disturbances, the anomalous extra-tropical cyclones (ECs) activity can exert important impacts on mid-latitude atmospheric circulation through the interaction with the time-mean flow. With global warming, variations in land surface thermal anomalies on the Eurasian continent will certainly affect atmospheric baroclinicity via the meridional temperature gradient, which can potentially alter ECs activity. Taking this as a starting point, we investigated the correlations between the variation in land surface thermal anomaly over the Eurasia and the ECs activity over East Asia and the relevant mechanisms using 1979-2013 ERA-interim reanalysis data.There is a distinct cyclogenesis area in the mid-latitude region of East Asia, the cyclogenesis frequency of this area has significant interdecadal changes. Before 1990, the cyclogenesis frequency is relatively high; in the 1990s to the present day, the cyclone activity is relatively weak.The land surface thermal anomaly has an decadal increasing trend. Because of the nonuniformity of the land surface warming, there is a key region north of 50° N which has a great influence on the cyclone activity of the cyclogenesis area. The decadal warming of the key region makes the meridional gradient of surface soil temperature of the cyclone source region decreased, leading to the weakness of the atmospheric baroclinicity, and the cyclogenesis frequency decreases correspondly.We found that the frequency of extra-tropical cyclogenesis is closely related to the atmospheric baroclinicity, and the time-mean effective potential energy is converted to eddy kinetic energy via the mediating effect of eddy effective potential energy. During years with high frequency of extra-tropical cyclogenesis, the surface soil temperature is relatively low in a key region north of 50°N, leading to an increase in the meridional gradient of surface soil temperature in the southern part of the cyclone source region, and an enhancement in the atmospheric baroclinicity. The associated baroclinic conversion term between the time-mean effective potential energy and the eddy effective potential energy increases, accompanied by an elevation in the eddy effective potential energy. The baroclinic conversion from the eddy effective potential energy to the eddy kinetic energy exhibits a positive anomaly, which increases the energy obtained by the synoptic-scale eddy from the time-mean flow, and favors the extra-tropical cyclogenesis.