Dissipation of wind waves by pancake and frazil ice in the autumn Beaufort Sea

A model for wind‐generated surface gravity waves, WAVEWATCH III®, is used to analyze and interpret buoy measurements of wave spectra. The model is applied to a hindcast of a wave event in sea ice in the western Arctic, 11–14 October 2015, for which extensive buoy and ship‐borne measurements were made during a research cruise. The model, which uses a viscoelastic parameterization to represent the impact of sea ice on the waves, is found to have good skill—after calibration of the effective viscosity—for prediction of total energy, but over‐predicts dissipation of high frequency energy by the sea ice. This shortcoming motivates detailed analysis of the apparent dissipation rate. A new inversion method is applied to yield, for each buoy spectrum, the inferred dissipation rate as a function of wave frequency. For 102 of the measured wave spectra, visual observations of the sea ice were available from buoy‐mounted cameras, and ice categories (primarily for varying forms of pancake and frazil ice) are assigned to each based on the photographs. When comparing the inversion‐derived dissipation profiles against the independently derived ice categories, there is remarkable correspondence, with clear sorting of dissipation profiles into groups of similar ice type. These profiles are largely monotonic: they do not exhibit the “roll‐over” that has been found at high frequencies in some previous observational studies. Key Points There is strong correspondence between observed ice type and independently estimated frequency‐dependent wave dissipation rate The dissipation versus frequency profiles do not exhibit the “roll‐over” effect reported in some prior observational and theoretical studies Cases with pancakes in frazil with visual indicators for thicker ice cover have highest dissipation rate, particularly at high frequencies