Characteristics of heat transfer over the ice covered Sea of Okhotsk during cold-air outbreaks

Heat transfer coefficients, and relative importance of factors affecting surface turbulent heat flux in sea-ice covered ocean, were investigated using data obtained by rawinsonde observations over, and around, the southwestern region of the Sea of Okhotsk from Jan. to Feb. in 1998, 1999 and 2000. The range of the fluxes estimated by an atmospheric heat budget analysis was large, associated with the ice concentration and synoptic situation. The turbulent heat fluxes from the open water surrounded by the sea ice are always positive (upward). However, the heat flux through sea-ice surface tends to be negative (downward) over sea-ice area associated with the relationship between the air and ice-surface temperature. Using the obtained turbulent heat fluxes and a bulk formula, relationships of turbulent heat fluxes with ice concentrations and atmospheric parameters were investigated, and a representative value of the bulk heat transfer coefficient was obtained. The estimated conditional bulk heat transfer coefficient (1.33 x 10(-3)) in the Sea of Okhotsk shows a smaller value than that in the Arctic region, reflecting the difference of the ice conditions, and thermal conditions in the boundary layer. Through an idea of the insulating coefficient, which measures degrees of the insulating effect of sea ice on the heat transfer, we explained that the sea ice works as a more effective insulator in weaker cold-air outbreaks. From a regression analysis, we found that the primary contribution to the amount of turbulent heat flux is the ice concentration, and second is the air temperature in the boundary layer.