Spatial Heterogeneity of Summer Turbulent Heat Exchange on the Plains of Russia

This work is aimed at analyzing the statistical characteristics of the heat balance of the underlying surface–atmosphere system on the plains of Russia with the identification of natural zones of maximum horizontal gradients, as well as assessing changes in the spatial heterogeneity of heat exchange in various landscape zones against the background of intense warming. Horizontal gradients of turbulent heat exchange are considered on the plains of Russia from the Arctic tundra to dry steppe and semideserts on average for the summer period of 1991–2020. The study involves the parameters of sensible and latent heat flux from the ERA5-Land reanalysis archive with a resolution of 0.1° × 0.1° in longitude and latitude. An analysis of the average, absolute, and relative variability of turbulent heat exchange, as well as their trends with an assessment of significance and horizontal gradients, is performed. Based on the maximum gradients of parameters, the areas of increased horizontal gradients of turbulent heat exchange are identified. In summer, one of the natural boundaries of increased horizontal gradients of heat exchange on the East European Plain and in Western Siberia (WS) is the middle taiga zone with adjacent parts of the northern and southern taiga. The heterogeneity of heat exchange in this area is due to the Arctic Front quasi-stationary secondary branch with an increased frequency of cyclones coming from the Atlantic–European sector and the location of high-altitude frontal zone here, which occurs at the junction of cold and warm air masses. The second natural boundary of increased heterogeneity of heat flows occurs in subboreal landscapes, where increased horizontal gradients of climatic parameters and surface characteristics are also noted. Here, the total radiation flow increases, the soil moisture deficit increases, and the amount of summer precipitation decreases. Spatial heterogeneity of turbulent heat exchange increased at the beginning of 21st century to the north of areas with maximum horizontal gradients of turbulent heat exchange. In the subarctic landscapes of WS, this growth is associated with general positive trends in surface temperature and with more frequent positive anomalies of summer temperature. In subboreal landscapes, a significant increase in heat exchange fluxes is mainly influenced by an increase in summer temperatures and a decrease in humidification with a simultaneous increase in the frequency of atmospheric blockings in the east of the East European Plain and in WS.