Warm-air advection, air mass transformation and fog causes rapid ice melt

Abstract

Direct observations during intense warm-air advection over the East Siberian Sea reveal a period of rapid sea-ice melt. A semistationary, high-pressure system north of the Bering Strait forced northward advection of warm, moist air from the continent. Air-mass transformation over melting sea ice formed a strong, surface-based temperature inversion in which dense fog formed. This induced a positive net longwave radiation at the surface while reducing net solar radiation only marginally; the inversion also resulted in downward turbulent heat flux. The sum of these processes enhanced the surface energy flux by an average of ∼15Wm-2 for a week. Satellite images before and after the episode show sea-ice concentrations decreasing from > 90% to ∼50% over a large area affected by the air-mass transformation. We argue that this rapid melt was triggered by the increased heat flux from the atmosphere due to the warm-air advection. Key Points The importance of both large-scale dynamics and local feedback for sea-ice melt The location of extra melt near the ice edge, due to the air-mass transformation The role of clouds, longwave radiation and turbulent heat flux for sea-ice melt.