Influence of Land-Atmosphere Coupling on Low Temperature Extremes Over Southern Eurasia

Land-atmosphere coupling is a crucial factor influencing extreme weather and climate. Based on the ERA5-Land reanalysis data set and sensitivity experiments with the CESM1.2.2 model, this study investigated the possible impacts of land-atmosphere coupling on low temperature extremes (LTEs) during fall and winter over southern Eurasia (SEA). The results suggested that LTEs show evident interdecadal variations in recent 60 years (1958-2017) and exhibit significant positive correlations with soil moisture anomalies based on the ERA5-Land data set. Numerical simulations (the control run and sensitivity run with prescribed climatological soil moisture) isolated the effects of soil moisture-related land surface processes and demonstrated that land-atmosphere coupling explains around 70% of temperature variability, increases the near-surface air temperature by 0.81 K, and favors the reduction of LTEs by 8.20 d.yr(-1). In the perturbation scenarios, the impacts of coupling on the frequency and spatial coverage of LTEs are more prominent. Further analysis revealed that the thermal cooling anomalies induced by the coupling could alter the atmospheric circulation, thereby affecting the frequency and intensity of LTEs. When the land-atmosphere interactions are weakened, the surface latent heat flux increases accompanied by intense evapotranspiration, while the sensible heat flux and net infrared radiation decrease. Land surface cooling is apparent, and it weakens with increasing altitude, along with geopotential height anomalies that are positive in the lower troposphere and weaker at higher altitudes. The northeasterly wind anomalies over the East European Plain facilitate the development of cold advection, providing a favorable circulation background for the generation of LTEs over SEA.

Automated summary

Land-atmosphere coupling has a significant impact on low temperature extremes during fall and winter over southern Eurasia. It explains around 70% of temperature variability, increases near-surface air temperature, and reduces the frequency of LTEs. The coupling also alters atmospheric circulation, affecting the frequency and intensity of LTEs.