Abstract
Abstract. We investigate a case of ocean waves through a pack ice cover captured by Sentinel-1A synthetic aperture radar (SAR) on 12 October 2015 in the Beaufort Sea. The study domain is 400 km by 300 km, adjacent to a marginal ice zone (MIZ). The wave spectra in this domain were reported in a previous study (Stopa et al., 2018b). In that study, the authors divided the domain into two regions delineated by the first appearance of leads (FAL) and reported a clear change of wave attenuation of the total energy between the two regions. In the present study, we use the same dataset to study the spectral attenuation in the domain. According to the quality of SAR-retrieved wave spectrum, we focus on a range of wave numbers corresponding to 9–15 s waves from the open-water dispersion relation. We first determine the apparent attenuation rates of each wave number by pairing the wave spectra from different locations. These attenuation rates slightly increase with increasing wave number before the FAL and become lower and more uniform against wave number in thicker ice after the FAL. The spectral attenuation due to the ice effect is then extracted from the measured apparent attenuation and used to calibrate two viscoelastic wave-in-ice models. For the Wang and Shen (2010b) model, the calibrated equivalent shear modulus and viscosity of the pack ice are roughly 1 order of magnitude greater than that in grease and pancake ice reported in Cheng et al. (2017). These parameters obtained for the extended Fox and Squire model are much greater, as found in Mosig et al. (2015) using data from the Antarctic MIZ. This study shows a promising way of using remote-sensing data with large spatial coverage to conduct model calibration for various types of ice cover.Highlights. Three key points: The spatial distribution of wave number and spectral attenuation in pack ice are analyzed from SAR-retrieved surface wave spectra. The spectral attenuation rate of 9–15 s waves varies around 10−5 m2 s−1, with lower values in thicker semicontinuous ice fields with leads. The calibrated viscoelastic parameters are greater than those found in pancake ice.
Highlights
Rapid reduction in Arctic ice in recent decades has become a focal point in climate change discussions (Comiso et al, 2008; Meier, 2017; Rosenblum and Eisenman, 2017; Stroeve and Notz, 2018)
Higher-frequency waves are preferentially attenuated; the power spectrum peak shifts to longer waves. Though this mechanism is supported by the increasing trend of ki with increasing wave number before the first appearance of leads (FAL), it is insufficient to explain the observations after the FAL, where the ki–kr curve is practically flat (Fig. 5), and the peak of the power spectral density (PSD) shifts toward lower kr with increasing latitude (Fig. 4)
We use the wave spectra retrieved from synthetic aperture radar (SAR) imagery to examine the spectral attenuation in young pack ice
Summary
Rapid reduction in Arctic ice in recent decades has become a focal point in climate change discussions (Comiso et al, 2008; Meier, 2017; Rosenblum and Eisenman, 2017; Stroeve and Notz, 2018). The reduction emphasizes the need to better understand the complex interaction between the sea ice, the ocean and the atmosphere. One of these interaction processes is between ocean waves and sea ice. Ocean waves help to shape the formation of new ice covers (Lange et al, 1989; Shen et al, 2001), break existing ice covers (Kohout et al, 2016), modify upper-ocean mixing (Smith et al, 2018) and potentially compress sea ice through wave radiation stress (Stopa et al, 2018a). S. Cheng et al.: Spectral attenuation of ocean waves in pack ice interaction by reducing the fetch. Cheng et al.: Spectral attenuation of ocean waves in pack ice interaction by reducing the fetch They alter wave dispersion and attenuation through scattering and dissipation (Squire, 2007, 2018, 2020)
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