Extreme Cold Events in North America and Eurasia in November-December 2022: A Potential Vorticity Gradient Perspective

From 17 November to 27 December 2022, extremely cold snowstorms frequently swept across North America and Eurasia. Diagnostic analysis reveals that these extreme events were closely related the establishment of blocking circulations. Alaska Blocking (AB) subsequent Ural (UB) episodes are linked phase transition Atlantic Oscillation (NAO) represent main atmospheric regimes in Northern Hemisphere. The downstream dispersion propagation Rossby wave packets from East Asia provide a large-scale connection between AB UB episodes. Based on nonlinear multi-scale interaction (NMI) model, we found meridional potential vorticity gradient (PVy) 2022 was anomalously weak mid-high latitudes Eurasia provided favorable background for prolonged maintenance generation associated severe snowstorms. However, difference terms its persistence, location, strength is positive (negative) NAO (December). During La Niña winter downward stratospheric anomalies, addition contributions by low Arctic sea ice concentrations as they pertain reducing PVy mid-latitudes.