Investigation of 2-dimensional isotropy of under-ice roughness in the Beaufort Gyre and implications for mixed layer ocean turbulence
McGeehan, Timothy P.
Stanton, Timothy P.
Shaw, William J.
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The two-dimensional (2D) spectral properties, including the degree of isotropy, of under-ice roughness in the Beaufort Gyre were investigated. Under-ice roughness plays an important role in turbulent ocean heat, salt, and momentum fluxes that determine the delicate balance between surface forcing and the ocean interior that sustains or reduces the perennial ice cover. Accurate characterization of this roughness is important for numerical modeling and prediction of the Arctic air-ice-ocean system, which will play a significant role as the US Navy increases its strategic presence in the ice-diminished Arctic Ocean. Ice draft data from moored upward looking echosounders of the Beaufort Gyre Exploration Project and ice motion derived from trajectories of International Arctic Buoy Program buoys were combined to create directional sections of ice draft. Autocorrelation functions were created for each segment which was then combined to make a 2D autocorrelation function. The 2D FFT was taken of this in order to yield a 2D spectrum, from which isotropy and other spectral properties could be determined. The processing routine was tested on several synthetic test datasets and in each case produced the correct output. Two years of data from three moorings in the Beaufort all provided 2D spectra which showed weak anisotropy of the under-ice roughness. Error estimates were determined by Monte Carlo simulations. For each dataset, most of the variance of the underside morphology was contained in a wavenumber band between 0.001 and 0.01m-1 (100-1000m). There were no distinct, preferred wavelengths. Spectral levels ranged from 1.2 - 4.2 x 104 m2 for Mooring C (2004-2005) to 0.2 - 1.6 x 104 m2 for mooring a (2004-2005).
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