Summertime atmosphere-ocean preconditionings for the Bering Sea ice retreat and the following severe winters in the North America

Abstract:

Atmospheric responses to sea ice retreat in the Bering Sea have been linked to recent extreme winters in North America. We investigate the leading factor for the interannual variability of Bering sea ice concentration (SIC) in early winter (November-December), using canonical correlation analysis based on seasonally resolved atmosphere and ocean data for 1980-2014. We found that the 3-month leading (August-September) geopotential height at 500 hPa (Z500) in the Northern Hemisphere explains 29% of SIC variability. The spatial pattern of Z500 for positive sea ice anomalies is associated with negative anomalies over the Gulf of Alaska related to the Pacific Transition (PT) pattern. The heat budget analysis indicates that summertime atmospheric conditions influence SIC through the ocean temperature anomalies of the Alaskan Coastal Current forced by atmospheric turbulent heat fluxes. The PT pattern highly correlates with convective precipitation in the western subtropical Pacific, implying that tropical forcing is the likely cause for the recent extreme winters in North America. Our results present a major factor for interannual variability in the Bering Sea ice area, and further would contribute to the improvement of forecast skill for winter climate in North America.