In recent decades, midlatitude continents frequently experienced severe winters despite increasing greenhouse gas concentrations. Several observational and modelling studies have suggested that the Arctic-to-midlatitude connection might have played a central role in the cold winters. However, it is highly controversial whether the Arctic-to-midlatitude connection is indeed driven by the Arctic sea-ice variability or is simply the result of internal atmospheric processes. Here we unravel this issue by presenting a time-varying midlatitude temperature response to the Arctic sea-ice variability. The low sea-ice concentration over the Barents-Kara-Laptev Seas in autumn typically leads cold Eurasian winters, suggesting delayed impacts that cannot be explained by internal atmospheric processes. More importantly, it is shown that the Arctic-to-midlatitude connection depends on the state of autumn atmospheric circulation. When the autumn sea-ice reduction is accompanied by anticyclonic circulation over northern Eurasia, Eurasia becomes anomalously cold in the early winter via the intensified continent high and monsoon trough. However, when cyclonic circulation is dominant, distinctive Eurasian cold anomalies appear in the late winter. This seasonally-delayed response is further found to be related to the wind-driven sea-ice drift that causes warm anomalies over the Barents-Kara-Laptev Seas in the following winter. These results indicate that the recent Eurasian cold winters could be largely explained by their forced response to the low Arctic sea-ice concentration.
GFDL Informal Seminar
Mon, Nov 18, 2019, 10:30 am to 11:30 am