Interdecadal change in the response of winter North Atlantic Oscillation to the preceding autumn sea ice in the Barents-Kara Seas around the early 1990s

Based on the reanalysis data for the period 1980-2019, this study reveals that the linkage of autumn sea ice concentration in the Barents-Kara Seas (BKSIC) to the subsequent winter North Atlantic Oscillation (NAO) underwent an interdecadal weakening in the early 1990s. Such a weakening is attributed to the discrepancy in the tropospheric warming resulting from the decrease in the interannual variability of the BKSIC from the former period to the latter period. During the former period (1980-1993), the decrease in autumn BKSIC can induce strong warming in the troposphere through enhancing the in-situ diabatic heating, significantly weakening the circumpolar westerly. The weakening of autumn circumpolar westerly then promotes the upward propagation of the Eliassen-Palm (EP) flux from the troposphere to the stratosphere. Till winter, the EP flux propagates downward from the stratosphere to the troposphere. It leads to significant positive stream function anomalies over the Greenland-Barents Seas region, accompanied with negative stream function anomalies over Western Europe. They are linked by a strong southeastward-propagating wave activity flux and result in a negative NAO phase with its southern center located eastward. During the latter period (1994-2019), due to smaller interannual variability of the BKSIC, its resultant warming of the tropospheric temperature is much weaker, not conducive to the aforementioned stratosphere-troposphere interaction and thus diluting the relationship between autumn BKSIC and the subsequent winter NAO.

Automated summary

This study, based on reanalysis data from 1980 to 2019, reveals that the relationship between autumn sea ice concentration in the Barents-Kara Seas (BKSIC) and subsequent winter North Atlantic Oscillation (NAO) underwent an interdecadal weakening in the early 1990s. The weakening can be attributed to the decrease in the interannual variability of BKSIC, which leads to a discrepancy in the tropospheric warming. In the former period (1980-1993), the decrease in autumn BKSIC enhances tropospheric warming and weakens the circumpolar westerly, resulting in a negative NAO phase. However, in the latter period (1994-2019), the smaller interannual variability of BKSIC weakens its influence on the tropospheric temperature, diluting the relationship with the subsequent winter NAO.