Growth of wave height with retreating ice cover in the Arctic

Quantitative relationships between retreating ice cover and the intensification of surface waves in the Arctic Ocean are studied. Wave data are produced by twelve-year (2007-2018) hindcasts of summer melt seasons (from May to September) and numerical tests with WAVEWATCH III. When a viscoelastic wave-ice model and a spherical multiple-cell grid are applied, simulated wave heights agree with available buoy data, altimeter data and previous simulations. Then, with the model data, we find that changes in mean significant wave height of the whole Arctic are dominated by changes in surface winds when the ice extent is larger than 9.4 x 10(6) km(2). If the ice extent retreats from 9.4 x 10(6) km(2), the model predicts that the mean significant wave height will increase by approximately 0.07 m (10(6) km(2))(-1) with comparable contributions from both increasing effective fetch and wind speed. For seven Arctic subregions, modeled significant wave height and probabilities of occurrence of large waves (significant wave height > 2 m, 3 m and 4 m) are shown positively correlated with the latitude of ice edge, and for modeled wind sea fraction, it is negatively correlated. With these results, we show the transition of surface waves from wind wave dominated to swell dominated in most of the Arctic sea areas with retreating ice cover. Assuming that the ice-free period occurs in September, the simulations show that mean wave height of the Arctic Ocean will increase to approximately 1.6 m with much more large waves. It implies that there will be a higher growth rate of wave height (m (km(2))(-1)) if the minimum ice extent continues to reduce in the future.