Effects Of Wet Isentropic Atmospheric Mass Circulation On Mid-high Latitude Surface Temperature In Winter

The Arctic experiences the most rapid increase of surface temperature in response to global warming,and the Arctic surface warming is often closely related to mid-latitude cooling in winter.However,there are still exceptions for the out-of-phase variations between the surface temperatures in mid-and high-latitudes,thus it is necessary to study the physical processes and mechanisms in depth.Using the latest ERA5 reanalysis data derived from the Interim European Centre for Medium-Range Weather Forecasts(ECMWF),this paper developed a transformed method to separate the dry and moist components of moist isentropic mass circulation(MIMC)based on the framework of MIMC,and revealed the respective roles of the dry and moist components of the MIMC in contributing to the daily changes in the extratropical surface temperature in winter.The main conclusions are as follows:The WB?M and WB?D indices are defined to measure the intensity of the moist and dry components,respectively,of the warm branch at 50°N-70°N,and WB?M is a better precursory indicator of Arctic surface warming,whereas WB?D is a better precursory indicator of surface cooling in mid-latitudes.This explains why the out-of-phase pattern of changes of the surface temperature in the polar region and at mid-latitudes is not always observed and provides new indicators for temperature changes in the Arctic and mid-latitude regions,respectively.The dynamical role of the MIMC in modifying downward longwave radiation through changing both the humidity of the Arctic air and the liquid water content of clouds leads to much more significant warming of the Arctic surface than the dynamical role of direct heat and energy transport,however,the dynamic process of the plenty of warm air transporting into polar region is accompanied by the negative phase of the Arctic Oscillation(AO)and the cold air pushed out of the Arctic due to mass continuity,thus has a better relationship with the mid-latitude surface cooling.There are also significant differences in the relationship between the dry and moist components of MIMC and the dominant mode of mid-latitude continental surface temperature anomalies.The Barents Sea-Northern Eurasian oscillation mode of the spatial distribution of surface temperature anomalies has a better relationship with the intensity of dry component of the warm branch at 70°N-75°N,while the Bering Sea-North America oscillation mode of the spatial distribution of surface temperature anomalies has a better relationship with the intensity of moist component of the warm branch at 60°N.The dry and moist components of MIMC regulate 200 h Pa jet streams,500 h Pa grooves and ridges,and surface weather systems in midhigh latitudes by affecting transport path of cold and warm air,thus affect the spatial distribution of surface temperature anomalies.