The influences of the Arctic troposphere on the midlatitude climate variability and the recent Eurasian cooling

Understanding the influence of the Arctic troposphere on the climate at midlatitudes is critical for projecting the impacts of ongoing and anticipated Arctic changes such as Arctic amplification and rapid sea ice decline over the Northern Hemisphere. In this study, we analyze a suite of atmospheric model experiments, with and without atmospheric relaxation toward reanalysis data, to study the impacts of the Arctic troposphere on the midlatitude atmospheric circulation and climate variability. The Arctic troposphere is found to strongly impact the interannual variability of the atmospheric circulation and temperature over the midlatitude continents. The major mechanisms for the impacts of Arctic troposphere include the modulation of the large-scale atmospheric circulation, the associated heat transport over the continents, and the impacts on synoptic variations in the North Atlantic-European sector. The impact of the Arctic troposphere on the intensity of the Siberian High is an important factor for how the Arctic can influence temperature variability in south Siberia and East Asia. The trends in the Arctic troposphere in recent decades are closely linked to the recent winter cooling in Northern Eurasia. These recent cooling trends are not driven by the trends in sea surface temperature/sea ice, tropical atmosphere, and the stratosphere. It is argued that the temperature trend pattern of warm Arctic-cold Eurasia is a manifestation of two possibly independent phenomena and the cooling trend is contributed to by the Arctic troposphere through impacting the large-scale atmospheric circulation, the atmospheric blocking frequency, and the intensity of the Siberian High.