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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]

Stratospheric volcanic aerosols can affect the global radiative balance and stratospheric composition. In this study, we analyze ensemble experiments with an interactive stratospheric aerosol microphysical general circulation model, designed to assess the climate forcing from large‐magnitude explosive eruptions in the tropics and northern extratropics. Previous studies have generally identified a lower radiative forcing from extratropical eruptions from the shorter stratospheric lifetime of volcanic sulfate aerosols. However, our study finds that both the shorter lifetime and lower effective radiative forcing (ERF) efficacy contribute to the lower ERF in the northern extratropical eruptions. The simulated 2‐year averaged ERF efficacy in northern extratropical eruptions is 22% lower than that in the equatorial eruptions due to the seasonal mismatch of peak stratospheric aerosol optical depth and solar radiation in the first year after a northern extratropical volcanic eruption. Additionally, equatorial eruptions accelerate the Brewer‐Dobson circulation (BDC), while northern hemispheric (NH) extratropical eruptions decelerate the BDC branch in NH and accelerate the BDC branch in southern hemisphere (SH), leading to different spatio‐temporal pattern of ozone anomalies. Consequently, dominated by the dynamical processes, equatorial eruption leads to ozone loss in tropics and increase in midlatitudes, while both northern extratropical summer and winter eruptions trigger ozone decrease in NH and increase in SH. Plain Language Summary: Volcanic eruption can introduce a large amount of SO2 into stratosphere, leading to perturbations of radiation and stratospheric compositions. Interactive model simulations show northern extratropical summer eruptions tend to produce ∼40% less effective radiative forcing (ERF) than equatorial eruptions. The differences tend to be attributed to the shorter lifetime of volcanic aerosols in the northern extratropics. We further find the comparable contribution of ERF efficacy (per unit aerosol optical depth), which is 22% less in northern extratropical eruptions than equatorial eruptions. This is attributed to the sulfate burden peak in the first winter with lower solar radiation in northern extratropical summer eruptions. The uneven distributions of sulfate aerosols also lead to varied responses of Brewer‐Dobson circulation (BDC) and ozone, and BDC transportation contributes more than chemical processes. Consequently, ozone loss in tropics and increase in midlatitudes for equatorial eruptions, while northern extratropical eruptions trigger ozone decrease in the injected hemisphere and increase in the opposite hemisphere. Key Points: Modeled shorter aerosol lifetime and less radiative forcing efficacy lead to ∼40% less radiative forcing in extratropical eruptionsSimulated effective radiative forcing efficacy in northern extratropical summer eruptions is 22% lower than that in equatorial eruptionsNorthern extratropical eruptions lead to distinct pattern of Brewer‐Dobson circulation and ozone change compared to equatorial eruptions [ABSTRACT FROM AUTHOR]

Based on multi‐model large‐ensemble experiments provided by Polar Amplification Model Intercomparison Project (PAMIP), we investigate the influence of the projected sea ice loss in Barents‐Kara Seas (BKS) and Sea of Okhotsk (SOK) on the Arctic stratospheric polar vortex (SPV). Results show that future BKS sea ice reduction leads to a weakened SPV during November‐February by enhancing the upward‐propagating planetary wave 1, which is more pronounced during Quasi‐Biennial Oscillation (QBO) easterly than westerly phase. Through weakening the upward‐propagating planetary wave 2, future SOK sea ice reduction is favorable for a strengthened SPV during January‐April. Inter‐model spread in the magnitudes of SPV responses to BKS sea ice reduction can be largely explained by the divergent planetary wave responses, but less so for SOK sea ice reduction. Results from a linearized baroclinic model further validate the importance of the planetary‐scale wave responses in explaining the differing SPV responses to sea‐ice loss over the two regions. Plain Language Summary: Arctic sea ice reduction influences the Northern Hemispheric weather and climate through modulating Arctic stratospheric polar vortex, which is a band of strong westerly encircling the pole during winter at ∼15–40 km above the Earth's surface. However, sea ice reduction over different regions could lead to different effects on the polar vortex. Here, we compare the effects of future sea ice reduction over the Barents‐Kara Seas, in the far‐north Atlantic Ocean, and the Sea of Okhotsk, in the northwest Pacific Ocean. We use carefully designed numerical simulations to estimate the effects of sea ice reduction, separately in the above‐mentioned two regions, on the polar vortex. Sea ice reduction over the Barents‐Kara Seas weakens the polar vortex, whereas sea ice reduction over Sea of Okhotsk strengthens the polar vortex. These contrasting effects are explained by opposing changes in wave activity entering the stratosphere from below. Barents‐Kara sea ice reduction leads to the strengthened upward propagating planetary waves, which break in the stratosphere and slow the polar vortex. Conversely, Okhotsk sea ice loss reduces upward waves and strengthens the polar vortex. Key Points: Barents‐Kara and Sea of Okhotsk sea ice loss weakens and strengthens polar vortex, respectively, with attendant changes in SSW frequencyPlanetary wave responses to Barents‐Kara and Okhotsk sea ice loss interfere constructively and destructively with mean flow, respectivelyPolar vortex weakening induced by Barents‐Kara sea ice loss is greater during easterly than westerly Quasi‐Biennial Oscillation phase [ABSTRACT FROM AUTHOR]

Using observations and CMIP6 historical simulations, the seasonal responses of Southern Ocean (50°S–70°S) sea surface temperature (SST) to Southern Annular Mode (SAM) variations are investigated in this study. The results suggest that the averaged Southern Ocean SST in austral spring and summer show a significant cooling in response to a positive SAM, while the responses in austral autumn and winter are negligible. The cooling effect is resulted from the cold water in higher latitudes and deeper oceans brought by the equatorward Ekman transport and the Ekman pumping associated with the positive SAM. Among CMIP6 models, the magnitude of the simulated cooling response connects to the climatological meridional and vertical ocean temperature gradients, and the magnitude of Ekman motion in response to SAM. In addition, the spring and summer SAM plays a more important role in modulating Southern Ocean SST in autumn and winter than the autumn and winter SAM. Plain Language Summary: Southern Annular Mode (SAM) is the first leading mode of atmospheric circulation in extratropical Southern Hemisphere and has an important influence on climate. This study evaluates the seasonal response of Southern Ocean SST to SAM variations in the CMIP6 historical simulations. We found that the regional averaged Southern Ocean sea surface temperature (SST) in austral spring and summer shows significant cooling signals in response to positive SAM. The responses of mean SST over Southern Ocean in austral autumn and winter to SAM during same seasons are not significant. The strengthening in Ekman transport and Ekman pumping in response to positive SAM would bring cold water from higher latitudes and deeper ocean to ocean surface, and hence, lead to a cooling effect. In addition, the simulations with a larger climatological meridional or vertical temperature gradient and stronger Ekman movements in response to positive SAM tends to generate a stronger cooling signal over Southern Ocean driven by positive SAM. Further analysis indicates that the austral spring and summer SAM has a more significant impact on Southern Ocean SST in austral autumn and winter, which might explain why the responses of Southern Ocean SST in austral autumn and winter to simultaneous SAM are not statistically significant. Key Points: The Southern Ocean sea surface temperature (SST) show a significant cooling in response to positive Southern Annular Mode (SAM) in austral spring and summerThe Ekman movements associated with enhanced SAM bring cold water from higher latitudes and deeper ocean, causing cooling effectsSAM in spring and summer play a more important role in modulating the autumn and winter SST than the SAM in autumn and winter [ABSTRACT FROM AUTHOR]