Abstract
Arctic sea-ice reduction has the potential to cause climatic change and extreme weather in the mid- and high-latitudes of the Northern Hemisphere. The causes of sea-ice variation, such as the influence of tropical sea surface temperature (SST) variation due to El Niño-Southern Oscillation, are actively studied. The notion that tropical SSTs influence atmospheric conditions in mid- and high-latitude regions is widely accepted. Nonetheless, the extent to which SSTs in the eastern tropical Atlantic drive sea-ice variability has not been extensively investigated. Here we show that autumn eastern tropical Atlantic convective cloud activity, independent of underlying SST, influences interannual variation in wintertime sea ice via atmospheric teleconnection with a lag of two months. In years characterized by heightened convective activity in October, Scandinavian anticyclonic anomalies emerge, driven by a wave train originating from the tropical Atlantic. This contrasts with years marked by inactive convection, which may be related to water vapor transport from the African Sahel. These anticyclonic anomalies facilitate the influx of warm, moist air into the Atlantic Arctic, thereby warming SST in the region and impeding the refreezing of sea ice. The convective activity affects not only the interannual variability of sea ice but also the decadal variability. Since convective activity in the tropical Atlantic is not driven by SST, SST may not serve as a reliable predictor for sea-ice forecasting. Clarifying the mechanisms underlying tropical atmospheric convection that are independent of SST is crucial for not only sea-ice forecasting, but also for predicting extreme weather in mid-latitudes.
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