Previous studies have shown non-stationary connections between Arctic sea-ice and extratropical weather regimes. In this study, including AER principal scientist Judah Cohen and scientists at NOAA and in China, we document the occurrences of these weather regimes in winter by their durations, based on the empirical orthogonal function (EOF) analyses of the daily geopotential height fields at 500 hPa (z500) for the months of November–March 1979–2019. Consistent changes in the occurrence frequency and persistence of Ural blocking (UB) and the lower stratospheric (100 hPa) polar vortex (PV) were found between high and low autumn sea-ice years (September–November in 15 years each). It is shown that the growth of the UB is accompanied with a weakening of the PV, and a weak PV favors more UB and long-duration (LD >5 days) Greenland blocking (GB). Cold spells in East Asia persist for five more days after an LDUB. Cold spells from Canada to U.S. occur 2–5 days after an LDUB- (negative phase) and are associated with a z500 anomaly dipole centered over Alaska (+) and the Hudson Bay (-). Cold spells in the eastern U.S. occur 1–4 days after an LDGB due to circulations resembling the Pacific-North America (PNA) pattern. Increased occurrences of UB in winter is associated with a decreased eastward propagation of synoptic waves from the North Atlantic to Japan and the North Pacific.
Figure. Composite mean of z500 anomalies (gpm) from 0-5 days after an LDUB+ event. Stippling indicates significant at a global p-value of 1% level based on a field significance test.
S. Fan, X. Chen, J. Cohen
Journal of Geophysical Research - Atmospheres, 129(11), e2023JD039868, 2024.