Velocity distributions of inelastically interacting ice floes driven by stochastic winds

The motion of sea ice on the ocean surface is driven primarily by stochastic winds and is resisted by water drag. However, observations show that the velocity distribution of sea ice is much broader than that of the driving winds. Here, we identify the quantitative mechanistic underpinnings of this observation by developing a stochastic dynamics framework of interacting ice floes. We model the wind as the superposition of a mean and a normally distributed single-correlation-time noise. This wind drives a dynamical system for the motion of sea ice floes that interact with each other through inelastic collisions. Through numerical particle-dynamics simulations, we find that the broadened velocity distribution of the ice is a direct and generic consequence of collisions. We rationalize these numerical results by developing a coarse-grained kinetic theory based on the Boltzmann equation for granular flows with drag, leading to analytic expressions for the velocity distributions. Extracting all physical inputs to the model from observational data, we show that both the simulations and the kinetic theory are in good quantitative agreement with observations of ice in the Fram Strait.