| Abstrakt: |
Using the ERA5 reanalysis data, we analyzed the impacts of the Arctic stratospheric polar vortex weakening on Ural Blocking (UB). The results indicate that UB activities are suppressed following the weakening of the polar vortex. Specifically, the probability of UB is significantly reduced, with a maximum decrease of 30% observed around day 24 following the polar vortex weakening. The average life cycle of UB shortens by approximately one day. The amplitude of UB, as measured by the negative potential vorticity (PV) anomalies over the Urals, experiences a significant decrease, particularly with the presence of positive PV anomalies on the western side of Urals. Further analysis indicates that the suppression of UB following the weakened polar vortex is closely linked to both the equatorward horizontal transport of high‐PV air over the Arctic across the dynamic tropopause, and the anomalous increase in static stability over the Urals resulting from a descent of the isentropic surface near the tropopause. Finally, we evaluate the relative roles of the polar vortex weakening and the negative phase of the Arctic Oscillation (AO) in suppressing the development of UB. Our analysis reveals that the impacts of the weak polar vortex on the suppression of UB are stronger and more long‐lasting compared to the negative AO, suggesting that the impacts of the weakened polar vortex on UB cannot be simply explained by the AO response. Plain Language Summary: Anomalies in the polar stratosphere, particularly the weakening of the stratospheric polar vortex, have been shown to significantly improve the predictability of the troposphere on Subseasonal to Seasonal (S2S) time scales. Ural blocking (UB), as an important factor driving the polar vortex weakening, has increasing importance in accurately forecasting the variability of the polar vortex. However, little is known about how the polar vortex affects UB, which is crucial as a better understanding of the dynamical links between them will likely benefit the development of the S2S and operational models. Here we investigate the impacts of the Arctic stratospheric polar vortex weakening on UB. Using statistical methods, we indicate a significant decrease in the probability of occurrence of UB days, as well as reductions in the intensity and average life cycle of the UB events following the polar vortex weakening. Through analyzing potential vorticity and Rossby wave breaking, we delve into the underlying mechanisms by which the weakened polar vortex impacts UB activities, and compare these mechanisms with the effects of the Arctic Oscillation (AO) pathway. Our findings underscore the potential value of a weakened stratospheric polar vortex in improving the predictability of UB activities on S2S time scales. Key Points: The polar vortex weakening suppresses Ural blocking (UB) activities, resulting in a maximum decrease of 30% in the probability of UBThis suppression is attributed to the equatorward transport of high potential vorticity air and the descent of the isentropic surfaceThe impacts of the weakened polar vortex on UB cannot be solely attributed to the response of the Arctic Oscillation [ABSTRACT FROM AUTHOR] |
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