Scaling Simulations of Local Wind-Waves Amid Sea Ice Floes

Abstract

Wave-ice interactions are critical for correctly modeling air-sea exchanges and ocean surface processes in polar regions. While the role of sea ice in damping open-water swell waves has received considerable research interest, the impact of sea ice on locally generated wind-waves in partial ice cover remains uncertain. The current approach in spectral wave models is to scale the wind input term by the open-water fraction, $1-\varphi$, for $\varphi$ the sea ice concentration (SIC), but this neglects the impact of subgrid-scale patterns of sea ice coverage in limiting fetch for wind-wave growth. Here, we use the spectral wave model SWAN to simulate local waves in realistic, synthetic fields of explicitly resolved sea ice floes over a range of SICs and floe size distributions (FSDs). We consider cases with floe sizes much larger than the wavelengths, and absent of interstitial frazil or pancake ice. Through geometric arguments, we show that the fetch available for wind-wave growth, and thus the resulting wave statistics, depends on a combination of the SIC and the FSD. The combination of geometric scaling and empirical wave laws allows the prediction of bulk wave statistics as a function of SIC, a characteristic floe size, and wind speed. We show that due to the difference in spectral character from attenuated propagating open-ocean swell, these waves may have an outsized impact on ocean mixing regimes.