Surface fluxes and atmospheric boundary layer budgets of enthalpy and momentum are quantified using bulk and integral methods based on measurements obtained during a research vessel transect across the Terra Nova Bay polynya during an intense late autumnal katabatic wind event. The surface sensible, latent, and net radiation heat fluxes had maximum upward values of 2,500 ± 600, 400 ± 100, and 100 ± 7 Wm−2, respectively, which occurred over open regions that had been cleared of sea ice by the wind stress. In these open areas, sea spray enhanced the sensible and latent heat fluxes (LHFs) by an estimated 106% and 18%, respectively. As sea ice formed on the surface and became thicker in the downwind direction, the sensible and LHFs decreased to 50% of their maximum values over pancake ice and to 5% at the downwind end of the transect, where snow‐covered young ice flows were present. Snow growth removed over 50% of the water vapor that came from the surface. The surface wind stress ranged from mean values of 2.9 Nm−2in the most upwind regions to 0.9 Nm−2at the end of the transect, with smaller scale variations of almost a factor of three due to different surface types (roughnesses) and gustiness. The downwind slowing and turning of the wind vector can be almost entirely explained by frictional and inertial forces, indicating the horizontal pressure gradient was weak. This case could serve as a case study for future modeling studies of coastal polynyas.
The atmospheric and surface conditions during a late autumnal strong katabatic wind event were quantified using ship and rawinsonde measurements over the Terra Nova Bay coastal polynya. Wind speeds decreased from 35 to 18 ms−1, while the wind direction decreased 18° over the distance from the Nansen Ice Shelf edge out 99 km eastward toward the Ross Sea. Maximum velocity winds (jet cores) at 173, 238, 179 and 144 m elevation were associated with atmospheric boundary layers capped by temperature inversions with bases at 294, 325, 226 and 196 m elevation. The tops of the inversion layers (near 700 m at all locations) also marked the top of the katabatic wind layer. Boundary layer air temperature and specific humidity increased from −31 to −21°C and 0.1 to 0.6 gkg−1, respectively, in response to the warm polynya surface. The air at 15 ± 8 m elevation was saturated with respect to ice, causing supersaturation and snow growth where the air parcels become cooler in the upper atmospheric boundary layer. The surface was characterized by three zones, a fluid zone (open ocean, frazil, shuga and pancake floes), an accumulation zone (fused, rafted and compressed pancake floes) and a young floe zone (large floes). The surface temperature varied from freezing (−1.7°C) in the fluid zone to near air temperature (−20°C) in the floe zone with the largest horizontal surface temperature gradient occurring in the transition between the fluid zone and the accumulation zone, and at the edges of leads in the floe zone.
more » « less- NSF-PAR ID:
- 10372596
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Atmospheres
- Volume:
- 126
- Issue:
- 20
- ISSN:
- 2169-897X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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