Surface energy budget over the central Arctic Ocean during late summer and early freeze-up

During the Arctic Ocean Expedition 1996 we measured radiative, turbulent, and conductive heat fluxes from late summer to early freeze-up, over the Norwegian Sea into the Arctic Ocean to latitude 88degreesN, mainly in air that had spent several days over the pack ice. In summer the net radiation was positive, on average +26 W m(-2), where the leads contributed more than the ice floes. Clouds had a cooling net effect. During the freeze-up period the net 2 radiation was dominated by the ice floes, on average -8 W m(-2), with a warming cloud net effect. The turbulent fluxes were on average small and unable to balance the net radiation except during cyclone activity, when the total turbulent heat fluxes averaged to +11 W m(-2) During the freeze-up period the conductive heat flux averaged to -4 W m(-2). In summer, melting of ice must largely have caused the average positive residual (+21 +/- 5 W m(-2)). During the freeze-up period the average negative residual (-7 +/- 3 W m(-2)) must result from formation of new ice and oceanic turbulent/convective fluxes in the leads. There was a diurnal cycle in net radiation both in summer (17 W m(-2) average amplitude) and the freeze-up period (8 W m(-2)) The turbulent sensible heat flux (average amplitude -5 W m(-2)), as well as the turbulent latent heat flux (1 W m(-2) in summer) and conductive flux in the ice (2.5 W m(-2) during the freeze-up) responded to this. These results emphasize the high sensitivity of the heat and radiation budget balances to changes in cyclone activity, leads, and clouds.