Mechanism of ice-band pattern formation caused by resonant interaction between sea ice and internal waves in a continuously stratified ocean

Abstract

In polar oceans, ice-band patterns are frequently observed around the ice edge in the winter, where sea ice production and melting continually occur. A better understanding of such fundamental processes in marginal ice zones (MIZs) may be key to accurate predictions of sea-ice evolution. Ice bands exhibit approximately 10-km-scale regular band spacings, and their long axes turn to the counter-clockwise (clockwise) with respect to the wind direction in the Northern (Southern) Hemisphere. We formulate a theory that is relevant for a continuously stratified ocean and compare the theoretical results with the numerical-model results and satellite observations. The numerical results quantitatively agree well with the theory. In particular, resonance condition, on which the phase speed of internal wave matches with the ice-band propagation speed, is always satisfied even if wind speed becomes slow. This is because there are an infinite number of baroclinic modes in continuously stratified ocean. We also show that an ice-band pattern emerges from a random initial ice concentration even though the wind is homogeneous. Plume-like ice bands along ice edge, which are frequently observed by satellites, are well explained by the pattern formation from random noise. Various effects of the ice-band formation were explored with respect to the relationship between the initial ice concentration and the wind direction, ice roughness, ice thickness, temporal variation of wind, and the Coriolis parameter.