The relationship between atmospheric blocking and Arctic-midlatitude thermal gradient

Atmospheric blocking is known to be one of the most important drivers of large-scale atmospheric variability at mid-high latitudes. Blocking events consist of a disruption and/or deceleration of the mean westerly circumpolar flow, and are generally associated with large-scale high-pressure patterns, which may be connected with the occurrence of climate extremes, such as heat waves and cold spells. Atmospheric dynamics in the Arctic region may be very important in shaping the spatial and temporal patterns of blocking at mid-high latitudes in the Northern Hemisphere, and consequently the occurrence of associated climate extremes. In particular, the difference between Arctic and mid-latitude temperatures is tightly associated with the Ural blocking (UB) activity. A causation relationship has been identified, with the UB triggering Arctic warming and Eurasian cold spells, and in turn leading to a weaker Arctic-midlatitudes thermal gradient (AMG).  The objective of this study is to investigate the physical mechanisms underlying the AMG-UB relationship. In particular, the circulation patterns associated with the nonlinear part of the UB-Arctic interannual relationship are analysed in winter (December-to-February) from 1940 to 2023. To this aim, atmospheric variables are extracted from the ERA5 reanalysis datasets. Results show that when high UB activity and strong AMG are observed, atmospheric blocking develops also over multiple areas relevant for milder and more humid air transport from mid latitudes into the Arctic region. Conversely, when low UB activity and weak AMG – hence associated with Arctic warmer than average – are observed, UB moves northwards, over Barents-Kara seas, and remote areas in the mid-latitudes and the subtropics, such as northwestern Africa and northwestern Atlantic Ocean, are teleconnected with the Arctic region. By highlighting the complex nature of the atmospheric blocking modulation of the AMG, these findings are relevant to the comprehension of the leading factors of Arctic Amplification, and to the understanding of the role of atmospheric blocking in determining winter cold spells and extreme temperature events over mid-latitude regions.