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 (DT) dropped rapidly with the accumulated fetch-width of leads up to about 35À40 km, and then decreased very slowly. The surface sensible heat flux originating from open water was about 300 W m À2 within a few kilometres from the coast and decreased with increasing accumulated fetch-width. The sensible heat flux was about 100 W m À2 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 0 T 0 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 0 q 0 ). The ratio between rising thermals (w þ T þ v ) and cold downdrafts (w À T À v ) differed significantly between upwind and downwind regions; that is, the buoyancy flux was dominated by w þ T þ v in the developing stage of the boundary layer, while w À T À v also became important after the development of the boundary layer.

Characterization and Parametrization of Reynolds Stress and Turbulent Heat Flux in the Stably-Stratified Lower Arctic Troposphere Using Aircraft Measurements

“…Flux-tower measurements by Mahrt and Vickers (2005) indicate that under statically stable conditions, turbulence becomes intermittent with countergradient transport of heat at large scales near the surface. Aircraft observations by Inoue et al (2005) identify positive heat flux within the statically stable Arctic lower troposphere associated with ice openings, which is indicative of countergradient transport. Various phenomena are suggested to cause countergradient transport of momentum and heat under statically stable conditions.…”

“…Even studies that attempt such measurements produce statistics that are informative but not necessarily directly useful for atmospheric model development. For example, Cho et al (2003) and Dehghan et al (2014) analyze aircraft measurements of turbulence using structure functions to derive dissipation rates ( ) in clear-air turbulence, and Inoue et al (2005) measured the heat flux over sea-ice using aircraft observations. However, these statistics do not reliably estimate turbulent diffusion coefficients (K m , K h ), which are relevant to turbulent flux parametrizations in the atmosphere (Hocking 1999).…”

Amplification of turbulent exchange over wide Arctic leads: Large‐eddy simulation study

“…The leads cover 1% to 5% of the central Arctic [Miles and Barry, 1998] and up to 20% of the Arctic marginal seas [Lindsay and Rothrock, 1995;Inoue et al, 2005]. Their importance is disproportional to their area coverage.…”

Influence of Okhotsk Sea Ice Distribution on a Snowstorm Associated with an Explosive Cyclone in Hokkaido, Japan

“…Because sea ice insulates the ocean from heat exchange with the atmosphere (e.g., Iwamoto et al 2001;Inoue et al 2005), the large seasonal and interanuual variability of the Okhotsk sea ice distribution influences local-to large-scale atmospheric phenomena. Nagata and Ikawa (1988) showed that the Okhotsk sea ice influenced the formation of convergent clouds west of Hokkaido Island using a numerical model.…”