Sea ice reduction is accelerating in the Barents and Kara Seas. Several mechanisms are proposed to explain the accelerated loss of polar sea ice, which remains an open question. In the present study, the detailed mechanism of sea ice reduction in winter is identified in the context of vertical processes using the daily ERA interim reanalysis data. Downward longwave radiation is an essential element for sea ice reduction, but can only be sustained by excessive upward heat flux from the sea surface exposed to air in the region of sea ice loss. The increased turbulent heat flux is used to increase air temperature and specific humidity in the lower troposphere, which in turn increases downward longwave radiation. This feedback process is clearly observed in the Barents and Kara Seas in the reanalysis data. A quantitative assessment reveals that this feedback process is amplifying at the rate of ~8.9 % every year during 1979-2016.
Energy budget is also analyzed over the region of sea ice reduction in order to delineate the relative roles of horizontal and vertical processes. A detailed energy budget in the atmospheric column indicates that the vertical processes such as the release of turbulent heat fluxes and upward longwave radiation is the ultimate cause of the increased temperature and specific humidity in the atmospheric column over the Barents-Kara Seas. Horizontal processes such as advection of heat and moisture are the major source of variability in temperature and specific humidity in the atmospheric column. On the other hand, they are less responsible for the increased winter mean of temperature and specific humidity associated with Arctic amplification.
Seminar Series Coordinators