This study investigates tropospheric midlatitude teleconnections associated with February Barents-Kara Sea (BKS) sea ice variability over the period 1979-2019 and finds evidence for changes in the teleconnections around the year 2000. Observational and modeling evidence suggests that these changes can be partly attributed to the weaker background stratospheric polar vortex after 2000 compared to the preceding two decades. Before 2000, BKS sea ice loss results in enhanced upward wave propagation and stratospheric wavenumber 1, but with a relatively weak tropospheric signature. After 2000, the weaker mean-state polar vortex suppresses vertical waves propagation into the stratosphere, confining the anomalous wave activity from BKS sea ice loss to the troposphere and thereby enhancing the East Asia trough. Additionally, slower tropospheric midlatitude westerlies after 2000, which are partly contributed by the weaker polar vortex, promote the westward migration of local ridge anomalies induced by BKS sea ice loss, enhancing the Greenland ridge. We propose that the stratospheric background state plays a crucial role in modulating the causal relationships between BKS sea ice variability and midlatitude circulation.
 

平流层极涡,北极海冰,中纬度天气