A Source Term for Wave Attenuation by Sea Ice in WAVEWATCH III(registered trademark): IC4
Naval Research Laboratory Stennis Space Center United States
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This document describes IC4, a new source term for attenuation of wave energy due to the presence of ice. IC4 was developed within the framework of WAVEWATCH III WAVEWATCH III Development Group, 2016. The design criterion for IC4 was a simple, efficient, and flexible implementation of frequencyperiod dependent wave attenuation. Within IC4, there are 6 methods called M1-M6. M1 to M4 are taken from the literature, though M1, M2, and M4 permit the user to modify the default coefficients. M5 and M6 are input methods for user-defined step functions. Herein, we describe in detail the implementation in the WAVEWATCH III framework, theoretical and empirical underpinnings of M1-6, give idealized examples, and present a case study based on the data from a field campaign sponsored by the Office of Naval Research. Considering the simplicity of the methods, performance of some IC4 methods in the case study was satisfactory. We demonstrate that frequency dependent attenuation in necessary to replicate the low-pass effect of wave-ice interaction. None of the methods performed universally well under varied ice conditions, which points to the major flaw of a one size fits all approach, i.e. attenuation derived from one kind of ice conditions will inevitably fail to reproduce attenuation under conditions which are quite different. We offer IC4 as simple alternative to more complex formulations of wave-ice interaction, but the user is cautioned to understand its limitations.
- Snow, Ice and Permafrost