In this study, detailed characteristics of the leading intraseasonal variability mode of boreal winter surface air temperature (SAT) over the North American (NA) sector are investigated. This intraseasonal SAT mode, featured by two anomalous centers with an opposite sign, one over central NA and another over East Siberia (ES) / Alaska, bears great resemblance to the “warm Arctic - cold continent” pattern of the interannual SAT variability over NA. This intraseasonal SAT mode and associated circulation exert pronounced influences on regional weather extremes, including precipitation over the northwest coast of NA, sea ice concentration over the Chukchi and Bering Seas, as well as extreme warm and cold events over the NA continent and Arctic region.
Surface warming and cooling signals of the intraseasonal SAT mode are connected to temperature anomalies in a deep tropospheric layer up to 300hPa with a decreasing amplitude with altitude. Particularly, a coupling between the troposphere and stratosphere is found during evolution of the intraseasonal SAT variability, although whether the stratospheric processes are essential in sustaining the leading intraseasonal SAT mode is difficult to be determined based on observations alone. Two origins of wave sources are identified in contributing to vertically propagating planetary waves near Alaska, one over ES/Alaska associated with local intraseasonal variability, another from the subtropical North Pacific via Rossby wave trains induced by tropical convective activity over the western Pacific, possibly associated with the Madden-Julian Oscillation.
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This article is included in the Connecting the Tropics to the Polar Regions Special Collection.