Estimation of surface heat flux based on radiosonde observation in the southwestern part of the Sea of Okhotsk under ice-covered condition

First radiosonde observation was performed in late January through early February in 1998 around the southwestern part of the Sea of Okhotsk to investigate the atmospheric boundary-layer modification and to estimate the turbulent fluxes of sensible and latent heat over ice-covered ocean during winter monsoon. Upstream cold and stable air mass originated from eastern Siberia was significantly modified through heat and moisture supply from warm sea surface with offshore cold-air outbreaks, which consequently formed mixed layer characterized by neutral stability over downstream areas. Associated with reduction of the top of the mixed layer height through the observational period, estimated heat fluxes also decreased gradually from 210 W/m^2 for partly ice-covered ocean to 30 W/m^2 for nearly perfectly ice-covered one, which are comparable with those of other marginal ice zones (the Bering Sea, the Greenland Sea, and so on). These decrease tendencies of the mixed layer height and estimated heat fluxes reflect the increase of the insulating effect of the sea-ice cover on heat and moisture exchanges between the atmosphere and ocean.