Article

Boundary-Layer Meteorology

, Volume 117, Issue 1, pp 111-129

First online:

Aircraft Observations of Air-mass Modification Over the Sea of Okhotsk during Sea-ice Growth

  • Jun InoueAffiliated withSchool of Earth and Atmospheric Sciences, Georgia Institute of Technology Email author 
  • , Masayuki KawashimaAffiliated withInstitute of Low Temperature Science, Hokkaido University
  • , Yasushi FujiyoshiAffiliated withInstitute of Low Temperature Science, Hokkaido University
  • , Masaaki WakatsuchiAffiliated withInstitute of Low Temperature Science, Hokkaido UniversityCore Research for Evolutional Science and Technology (CREST), Japan Science and Technology Agency

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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 m−2 within a few kilometres from the coast and decreased with increasing accumulated fetch-width. The sensible heat flux was about 100 W m−2 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 \(\left(\overline {w'T \, '_v}\right)\) 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 \((\overline {w'q'})\). The ratio between rising thermals \(\left(\overline {w^+T^+_v}\right) \) and cold downdrafts \(\left(\overline {w^-T^-_v}\right)\) differed significantly between upwind and downwind regions; that is, the buoyancy flux was dominated by \(\overline {w^+T^+_v} \) in the developing stage of the boundary layer, while \(\overline {w^-T^-_v} \) also became important after the development of the boundary layer.

Keywords

Accumulated fetch-width of leads Leads Sea-ice Sea of Okhotsk Turbulent heat flux