Author(s): Sukun Cheng; Justin Stopa; Fabrice Ardhuin; Hayley H. Shen
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Abstract: Sea ice reduction has increased the fetch and wave intensity in the Arctic Ocean. Reliable wave forecasts will be useful for the potential increase of engineering activities in the region, and help to evaluate present and future oceanographic and meteorological processes that may be affected. The global wave model WAVEWATCH III® has implemented several “switches” to determine the propagation of ocean waves through an ice cover. Except for one switch which is entirely data-driven, each of the other switches is based on a different theory and requires field data to calibrate the parameters. These switches, when trained with large amounts of data, can become robust for applications. In this paper, we present the methodology and results of using field data to calibrate one of these switches based on a viscoelastic theory. In this theory, the ice covers are assumed to be solely responsible for the observed change in wave dispersion and attenuation. The two parameters of an ice cover, equivalent elasticity and viscosity, depend on the type of the ice cover. We study two types of ice covers. One predominantly consists of grease and pancake ice near the ice edge. The other is pack ice further into the ice cover. We also divide the pack ice zone into two subzones delineated by the first appearance of leads. The calibrated equivalent shear modulus (viscosity) of the pack ice are roughly two orders (one order) of magnitude greater than that in grease/pancake ice. Small but notable changes of viscoelastic parameters are also found before and after the first appearance of leads. The same methodology used in the analysis is also applicable to calibrate other switches. These completed switches may then be used in WAVEWATCH III® to evaluate their forecast capabilities.
Year: 2020