Comparing Observations and Parameterizations of Ice‐Ocean Drag Through an Annual Cycle Across the Beaufort Sea. Issue 4 (28th April 2021)

• Record Type: Journal Article
• Authors: Brenner, Samuel; Rainville, Luc; Thomson, Jim; Cole, Sylvia; Lee, Craig
• Is Part Of: Journal of geophysical research. Volume 126:Issue 4(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-04-28
• Subjects: air/sea/ice exchange -- Beaufort Sea -- drag parameterization -- ice‐ocean drag -- sea ice momentum -- sea ice morphology; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2020JC016977
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Understanding and predicting sea ice dynamics and ice‐ocean feedback processes requires accurate descriptions of momentum fluxes across the ice‐ocean interface. In this study, we present observations from an array of moorings in the Beaufort Sea. Using a force‐balance approach, we determine ice‐ocean drag coefficient values over an annual cycle and a range of ice conditions. Statistics from high resolution ice draft measurements are used to calculate expected drag coefficient values from morphology‐based parameterization schemes. With both approaches, drag coefficient values ranged from ∼1 to 10 × 10 −3, with a minimum in fall and a maximum at the end of spring, consistent with previous observations. The parameterizations do a reasonable job of predicting the observed drag values if the under ice geometry is known, and reveal that keel drag is the primary contributor to the total ice‐ocean drag coefficient. When translations of bulk model outputs to ice geometry are included in the parameterizations, they overpredict drag on floe edges, leading to the inverted seasonal cycle seen in prior models. Using these results to investigate the efficiency of total momentum flux across the atmosphere‐ice‐ocean interface suggests an inter‐annual trend of increasing coupling between the atmosphere and the ocean. Plain Language Summary: Sea ice moves in response to the push and pull (a.k.a., "drag") of both wind and ocean currents, so speeds of both the ice and the underlying ocean depends on how efficient that drag is. By looking at measurements of ice motion in response to the wind and ocean currents from three sites in the Beaufort Sea, we have calculated drag efficiency over 1 year. Computer models predict drag efficiency based on how rough the bottom of the sea ice is. Our measurements of the shape of the sea ice bottom are used to test and verify the framework for calculating drag efficiency that is in place in those models. The model framework can do a reasonable job of prediction if given good measurements of how rough the ice is, but may not be good at predicting that roughness. Because of that, current models might overpredict the drag efficiency while ice is melting. With our measurements of drag efficiency, we calculate how the sea ice impacts the total ability of the wind to push on the ocean and find that it is enhanced by the sea ice. As Arctic sea ice becomes more seasonal, we expect this enhancement to increase. Key Points: In situ measurements are used to estimate ice‐ocean drag across a wide range of ice conditions based on the sea ice momentum balance Ice‐ocean drag coefficients show a seasonal cycle with a spring maximum and a fall minimum, following the growth and melt of ice keels Geometry‐based drag parameterization schemes are able to capture much of the observed variability using direct ice geometry measurements