Wintertime Expansion and Contraction of the
Terra Nova Bay Polynya
M.L. Van Woert
NOAA/NESDIS/Office of Research and Applications E/RA3, World Weather Building
Room 711,4700 Silver Hill Road Stop 9910, Washington, DC 20233-9910, USA
Abstract
A one-dimensional Coastal polynya model, forced by data from a near-by automatic weather station, is used to examine wintertime ice concentration fluctuations in the Terra Nova Bay polynya. It has long been believed that the Terra Nova
Bay polynya opens in response to strong offshore katabatic wind forcing. This
study shows that not only is the sensible heat flux important in controlling fluctuations in polynya extent, but that the longwave heat fluxes is important also.
Moreover, this study shows that wind forcing becomes important to the polynya
dynamics as an amplification factor acting on the longwave flux term. Together
these two terms can explain up to 40% of the observed variance in open water
fraction. Some large-amplitude fluctuations in open water fraction at Terra Nova
Bay were not well modeled in this study. These anomalies are believed to be related to large-scale changes in the Ross Sea pack ice, which are driven by strong
winds blowing off the Ross Ice Shelf. Ice production rates were found to be comparable with historical estimâtes. To maintain a conversion of Warm Core Water
or Low Salinity Shelf Water (S=34.5PSU) to High Salinity Shelf Water (S=34.8
PSU) consistent with the observed ice production rate, a transport of approximately 1 Sv is required at Terra Nova Bay.
1 Introduction
Polynyas are recurring régions of either partially or totally ice-free océan occurring within the pack ice at times when air températures are well below the freezing point of seawater. Polynyas forming in Coastal régions where strong and persistent offshore winds drive newly formed sea ice offshore are often referred to as
latent heat polynyas [1], because latent heat is produced by the freezing of ice.
These polynyas are particularly important because they typically occur on the
polar continental shelves where the water is already close to the freezing point.
Brine rejected during the ice formation process further densifies the water column leading to cold saline water masses that spill off the continental shelves into
the deep océan basins. Studies in the Arctic (e.g. [2,3]), Antarctic [4-6], and high
latitude marginal seas [7] hâve attempted to estimate water mass formation rates
in Coastal polynyas by combining satellite-derived estimâtes of open water fraction with estimâtes of the ice production rate based on net atmospheric flux data.
Terra Nova Bay Polynya
M.L. Van Woert
NOAA/NESDIS/Office of Research and Applications E/RA3, World Weather Building
Room 711,4700 Silver Hill Road Stop 9910, Washington, DC 20233-9910, USA
Abstract
A one-dimensional Coastal polynya model, forced by data from a near-by automatic weather station, is used to examine wintertime ice concentration fluctuations in the Terra Nova Bay polynya. It has long been believed that the Terra Nova
Bay polynya opens in response to strong offshore katabatic wind forcing. This
study shows that not only is the sensible heat flux important in controlling fluctuations in polynya extent, but that the longwave heat fluxes is important also.
Moreover, this study shows that wind forcing becomes important to the polynya
dynamics as an amplification factor acting on the longwave flux term. Together
these two terms can explain up to 40% of the observed variance in open water
fraction. Some large-amplitude fluctuations in open water fraction at Terra Nova
Bay were not well modeled in this study. These anomalies are believed to be related to large-scale changes in the Ross Sea pack ice, which are driven by strong
winds blowing off the Ross Ice Shelf. Ice production rates were found to be comparable with historical estimâtes. To maintain a conversion of Warm Core Water
or Low Salinity Shelf Water (S=34.5PSU) to High Salinity Shelf Water (S=34.8
PSU) consistent with the observed ice production rate, a transport of approximately 1 Sv is required at Terra Nova Bay.
1 Introduction
Polynyas are recurring régions of either partially or totally ice-free océan occurring within the pack ice at times when air températures are well below the freezing point of seawater. Polynyas forming in Coastal régions where strong and persistent offshore winds drive newly formed sea ice offshore are often referred to as
latent heat polynyas [1], because latent heat is produced by the freezing of ice.
These polynyas are particularly important because they typically occur on the
polar continental shelves where the water is already close to the freezing point.
Brine rejected during the ice formation process further densifies the water column leading to cold saline water masses that spill off the continental shelves into
the deep océan basins. Studies in the Arctic (e.g. [2,3]), Antarctic [4-6], and high
latitude marginal seas [7] hâve attempted to estimate water mass formation rates
in Coastal polynyas by combining satellite-derived estimâtes of open water fraction with estimâtes of the ice production rate based on net atmospheric flux data.