Air‐ice drag coefficients for first‐year sea ice derived from aircraft measurements

In March 1981, detailed meteorological observations were made at the marginal ice zone in the Bering Sea during a period of northerly winds. A 20% increase in wind speed from 90 km inside the edge to 90 km over the ocean was observed. The temperature increased from −11°C to −5°C, and the boundary layer height over the ocean increased from 450 m to 600 m. Data support the concept of a diverging (accelerating) flow. A simple integrated slab model of the atmospheric boundary layer which includes the effects of clouds, surface heat flux, and radiative cooling is applied to the conditions of the marginal ice zone. The model shows that most of the observed variation in the marginal ice zone can be explained by drag variation over the ice and heat flux over the open ocean. Heat flux in the marginal ice zone and cloud processes affect the results only slightly.

Section: Discussionmentioning

confidence: 88%

On the local meteorology at the marginal ice zone of the Bering Sea

Reynolds¹

1984

“…where Pa is the air density and C ai is a drag coefficient. The drag coefficient at the air-ice interface (Cai) will be chosen to be twice as large as that at the air-water interface (Caw) but is still somewhat smaller than the measured value under slightly unstable atmospheric conditions [Walter et al, 1984]. In this application, U•o is either uniform or Gaussian, given by either where Pw is the seawater density and U is the surface ocean current.…”

Section: Tat--pacai U101u10 (3)mentioning

confidence: 99%

“…The drag coefficient at the air-ice interface (Cai) will be chosen to be twice as large as that at the air-water interface (Caw) but is still somewhat smaller than the measured value under slightly unstable atmospheric conditions [Walter et al, 1984]. …”

Section: Paper Number 1999jc900159mentioning

confidence: 99%

Ocean feedback to wind‐driven coastal polynyas

Chao¹

1999

Abstract. For lack of observations, a coupled numerical model of an ice layer and a coastal ocean is used to conduct thought experiments on the evolution of wind-driven coastal polynyas. Attention is focused on the possible ocean feedback to polynya developments before and after wind relaxation. The coupled system is initially motionless, having an ice layer of uniform concentration and thickness. In the ocean, the salinity is initially uniform and the temperature is at the freezing point. Subsequent cold air outbreaks of several days in duration push the ice layer offshore. Frazil is produced and collected in the polynya owing to continuous heat loss to the atmosphere. Ocean feedback is particularly effective after wind relaxation. Under large-scale seaward winds, the displaced ice edge does not return landward after wind abatement if the wind event is strong and long. Over a sizable coastal bottom obstacle, however, anticyclonic circulation develops and its landward arm may force a landward return of the ice edge after wind relaxation. Further, dipole vortices in the ocean may develop under a mesoscale seaward wind event. Landward ocean currents around the rim of a dipole may also force a postwind return of the ice edge. The ocean feedback is generally stronger and faster in shallower basins; this can be demonstrated by a one-dimensional, stress-driven coastal ocean model. IntroductionCoastal polynyas are openings of ice-free regions in the coastal ocean. In winter, coastal polynyas are often produced by seaward winds. If the air and water are cold enough to produce ice, the new frazil racing toward the seaward retreating ice layer may limit the maximum width of a coastal polynya [Lebedev, 1968]. A simple ice layer model [Pease, 1987] was formulated following this idea and compared favorably with limited observations. Pease's model is kinematic, assuming that newly formed frazil in open water is instantaneously collected at the ice edge. Her model was later generalized to incorporate finite drift speed of frazil [Ou, 1988]

“…Aircraft are ideal platforms for quickly obtaining detailed spatial information on atmospheric structure and dynamics. However, since the covariance technique to determine wind stress usually requires averaging over a path length of at least 30 km [e.g., Walter et al, 1984;Fairall and Markson, 1987;Walter and Overland, 1991] Over open ocean there was also a sloping inversion, but a horizontal temperature gradient within the ABL counteracted the baroclinic effect at the surface, resulting in a factor B value of 1.00. Kellner et al [1987] found that the wind stress in the region just inside the ice edge over was about 40% lower than the open ocean (Table 1 and Figure 1, curve 2), based on an aircraft flight during slightly off-ice winds in the Fram Strait MIZ on July 7, 1984.…”

Section: Aircraft Measurementsmentioning

confidence: 99%

An observational and numerical study of wind stress variations within marginal ice zones

Guest¹,

Glendening²,

Davidson³

1995

Published studies of ocean mesoscale processes in marginal ice zones (MIZs) using numerical coupled ice‐ocean models usually assume that the surface wind speed is constant over the model domain and that wind stress variations are simply proportional to surface roughness variations. We show that this assumption is not realistic in most situations because the surface wind stress is also significantly affected by mesoscale pressure variations, by changes in the surface wind vector, and by changes in surface layer stability. Two numerical case studies, utilizing detailed surface and atmospheric measurements, examine the factors affecting small‐scale (<5 km) variations in wind stress within MIZs. These case studies and surveyed observational and modeling results demonstrate that wind stress fields are qualitatively different from the surface roughness fields. A realistic wind stress scenario consists of a maximum just inside the ice edge and another maximum in the open ocean. Stress minima occur within the pack ice region away from the MIZ and over grease ice, if present. The effect of the rougher MIZ ice is counteracted when wind stresses over the open ocean are enhanced by large surface heat fluxes over the ocean, by a strong low level inversion over the ice, or by a sharp atmospheric front with surface winds paralleling the ice edge. Such situations are common in MIZ regions. Some simple methods for including first‐order atmospheric effects on wind stress variations, which could be incorporated into current ice‐ocean mesoscale models of MIZ regions, are suggested.