The redistribution of heat within the Arctic atmosphere during years with very low sea ice extent

WRF model simulations are made in which we use the sea ice thickness fields estimated by an off-line coupled ice-ocean model as a lower boundary condition. The goal is to better understand the fate within the atmosphere of the extra heat absorbed by the ocean in low ice years. How much is quickly lost to space and how much reduces ice growth rates during winter? Atmospheric heat fluxes and transports are compared for ice conditions from 2007 (the year with the minimum ice extent) and from the median ice conditions since 1979. The domain includes the entire Arctic Ocean, the grid size is 60 km, and there are 52 vertical levels. Lateral forcing is from the NCEP GFS analysis and the months of July through December are simulated in an ensemble of paired experiments, low ice versus median ice conditions.

There is a very large increase in the turbulent flux in the open water seen with the 2007 ice conditions, on the order of 100 W/m2, but the net surface longwave flux does not change significantly. The heat flux convergence within the atmospheric column is reduced because of the surface turbulent fluxes. While there is reduced heat convergence in the open water areas, there is increased convergence in other locations because of the export of heat from the open water and thin ice regions. The increase in the outward longwave flux at the top of the atmosphere is modest and about half of the mean increase in the surface turbulent fluxes, so much of the extra heat from the ocean is distributed within the system and not simply lost to space.