Ocean surface waves tend to be attenuated by interaction with sea ice. In this study, six sea ice models in the third-generation wave model WAVEWATCH III® (WW3) were used to estimate wave fields over the Sea of Okhotsk (SO). The significant wave height (Hs) and mean wave period (Tm) derived from the models were evaluated with open ocean and ice-covered conditions, using SO coastal area buoy observations. The models were validated for a period of 3 years, 2008–2010. Additionally, the impact of sea ice on wave fields was demonstrated by model experiments with and without sea ice. In the open ocean condition, the root-mean square error (RMSE) and correlation coefficient for hourly Hs are 0.3 m and 0.92, and for hourly Tm 0.97 s and 0.8. In contrast, for the ice-covered condition, the averaged RMSE and correlation coefficient from all models are 0.44 m (1.6 s) and 0.8 (0.6) for Hs (Tm), respectively. Therefore, except for the bias, the accuracy of model results for the ice-covered condition is lower than for the open water condition. However, there is a significant difference between the six sea ice models. For Hs, the empirical formula whereby attenuation depends on the frequency relatively agrees with the buoy observation. For Tm, the empirical formula that is a function of Hs is better than those of other simulations. In addition, the simulations with sea ice drastically improved the wave field bias in coastal areas compared to the simulations without sea ice. Moreover, sea ice changed the monthly Hs (Tm) by more than 1 m (3 s) in the northwestern part of the SO, which has a high ice concentration.

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Antidunes are fluvial bedforms that form in rivers with supercritical flows. The water surface over antidunes is strongly in phase with the bed surface, and the water surface is amplified to produce large surface waves. Many experimental studies have addressed antidunes; however, the shapes of three‐dimensional antidunes in a wide channel with alternate bars have not yet been appropriately understood. In this study, we experimentally investigated the streamwise and transverse length scales of antidunes under conditions with a large width–depth ratio. Our experimental results provide evidence for the coevolution of antidunes and free alternate bars, and show for the first time that the development of free bars greatly alters the three‐dimensional shape of water surface waves over antidunes. In the absence of free bars in a wide channel, multiple longitudinal wave trains form, and the number of wave trains counted in the transverse direction increases with increases in the width–depth ratio. However, the presence of free bars affects the local flow characteristics, resulting in a decrease of the number of wave trains in the transverse direction. Therefore, we propose a simple model for predicting the reduction in the number of wave trains by combining two previous theories for antidunes and free bars. Results obtained by the model were found to largely agree with experimental observations. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

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