Floe Size Effect on Wave‐Ice Interactions: Possible Effects, Implementation in Wave Model, and Evaluation

Abstract

Wind waves may play an important role in the evolution of sea ice. That role is largely determined by how fast the ice layer dissipates the wave energy. The transition from a continuous layer of ice to a series of broken floes is expected to have a strong impact on the several attenuation processes. Here we explore the possible effects of basal friction, scattering, and dissipation within the ice layer. The ice is treated as a single layer that can be fractured in many floes. Dissipation associated with ice flexure is evaluated using an anelastic linear dissipation and a cubic inelastic viscous dissipation. Tests aiming to reproduce a Marginal Ice Zone are used to discuss the effects of each process separately. Attenuation is exponential for friction and scattering. Scattering produces an increase in the wave height near the ice edge and broadens the wave directional spectrum, especially for short-period waves. The nonlinear inelastic dissipation is larger for larger wave heights as long as the ice is not broken. These effects are combined in a realistic simulation of an ice break-up event observed south of Svalbard in 2010. The recorded rapid shift from a strong attenuation to little attenuation when the ice is broken is only reproduced when using a nonlinear dissipation that vanishes when the ice is broken. A preliminary pan-Arctic test of these different parameterizations suggests that inelastic dissipation alone is not enough and requires its combination with basal friction. Key Points:• A spectral wave model with effects of sea ice floe size is presented • Ice breakup is combined with three attenuations processes • Model wave heights for a break-up event reproduce observations in Svalbard apply to wide fields of pancakes that are found in the freezing season and but should rather be representative of waves interacting with solid ice pack. In these conditions, our goal is to explore plausible regimes of wave attenuation in the MIZ, given certain assumptions about wave-ice interaction processes.The different mechanisms that have been proposed to explain wave attenuation in the ice can be represented by source terms in the wave action equation describing the evolution of the wave field (Masson & LeBlond, 1989). The relative importance of the different mechanisms is still unknown in conditions encountered in the natural environment (Squire, 2007). Robin (1963) measured wave attenuation in the Weddel Sea but did not conclude on its possible source, mentioning anelastic dissipation (hysteresis) and basal friction as possible explanations. Wadhams (1973) hypothesized that wave could be dissipated by secondary creep, namely, the inelastic dissipation of waves due to the ice flexure, with a strain rate proportional to the cube of the stress, following the flow law used by Glen (1955) for very slow glacier motions. The work done during and after MIZEX emphasized scattering, that is, multiple reflections of waves by floes, as the dominant source of wave attenuation (Kohout & Meylan, 2008;Kohout et al., 2014;Montiel et...

Overview of the Arctic Sea State and Boundary Layer Physics Program

“…Stopa et al (2018) have also determined attenuation further into the ice pack during Wave Experiment 3, using a larger domain thanks to wave heights derived from Sentinel 1 SAR imagery. The associated processes appear very different from what is found in pancake ice and is described by Boutin et al (2018) and discussed by Ardhuin et al (2018). Montiel et al (2018) further analyze wave attenuation and directional spreading during the large wave event of Wave Experiment 3.…”

Impact of floe size distribution on seasonal fragmentation and melt of Arctic sea ice

“…A recent study has found that the basal melt rate may also be influenced by floe size (Horvat and Tziperman, 2018). Floe size can also impact the propagation of waves under the ice (Boutin et al, 2018;Meylan and Squire, 1994;Squire, 2007). The assumption of a fixed floe size also precludes sea ice models from accurately representing the role of processes within sea ice evolution that can change floe size such as lateral melting and wave induced fragmentation of floes.…”

Wave‐Induced Surge Motion and Collisions of Sea Ice Floes: Finite‐Floe‐Size Effects

“…Sea ice in the region typically referred to as the marginal ice zone (MIZ)—by definition influenced by the action of waves—may have different concentration, thickness, and mechanical properties and may consist of different ice types, from compact, semicontinuous ice sheet, through large, thick ice floes (bare or covered with snow) and crushed ice pieces, pancake ice, to a dense mixture of frazil crystals and water. In recent years, the transformation of waves as they propagate through sea ice—different types of sea ice—has become subject of extensive observational and theoretical research (Ardhuin et al, ; Bennetts & Squire, ; Boutin et al, ; Kohout & Meylan, ; Kohout, Meylan, & Plew, ; Meylan, Bennetts, & Kohout, ; Squire, ; Sutherland, Christensen, & Rabault, , and references therein). The observed attenuation rates in sea ice (see, e.g., the recent study by Stopa et al, ) vary over a few orders of magnitude, from less than 10 −6 m −1 to over 10 −3 m −1 , suggesting that different combinations of processes are responsible for the decay of wave energy in different ice and wave conditions.…”