Aircraft observations of air-mass modification over the sea of Okhotsk during sea-ice growth

Abstract

In order to quantitatively investigate the role of leads and sea-ice in air-mass modification, aircraft observations were conducted over the partially ice-covered Sea of Okhotsk. We investigated two cold-air outbreak events with different sea-ice concentrations. In both cases, the difference between the temperatures of surface air and the sea surface (ΔT) dropped rapidly with the accumulated fetch-width of leads up to about 35-40 km, and then decreased very slowly. The surface sensible heat flux originating from open water was about 300 W m2 within a few kilometres from the coast and decreased with increasing accumulated fetch-width. The sensible heat flux was about 100 W m2 on average. These results indicate that the downwind air-mass modification depends mainly on the total (accumulated) extent of open water. The total buoyancy flux (W′T′v) calculated by the joint frequency distribution method correlated very well with ice concentration. Such a relationship was not clear in the case of the moisture flux (w′ q′). The ratio between rising thermals (w+Tvv) and cold downdrafts (w-Tv-) differed significantly between upwind and downwind regions; that is, the buoyancy flux was dominated by W+Tv+ in the developing stage of the boundary layer, while W- T-v also became important after the development of the boundary layer. © Springer 2005.