Arctic sea ice velocity field: General circulation and turbulent-like fluctuations

International audienceUsing buoy trajectories of the IABP data set, we analyze the Arctic sea ice velocity field as the superposition of a mean field and fluctuations. We study how the mean field can be objectively defined, using appropriate spatial and temporal averaging scales depending on the season considered: 400 km and 5 1/2 months for winter (i.e., approximately all the polar winter duration), and 200 km and 2 1/2 months for summer (i.e., approximately all the polar summer duration). The mean velocity field shows a strong intra-annual (between winter and the following summer) as well as interannual variability. The fluctuations, i.e., the remaining part of the velocity field after subtracting the mean field, are analyzed in terms of diffusion properties. Although the Arctic sea ice cover is a solid, we show that the fluctuations follow the same diffusion regimes as the ones predicted for turbulent flows, as observed in geophysical fluids like the ocean or the atmosphere. We found that the integral time and the diffusivity of sea ice are in the same ranges as those estimated for the ocean, i.e., 1.5 days in winter and 1.3 days in summer and 0.44 x 10(3) m(2)/s for winter and 0.45 x 10(3) m(2)/s in summer, respectively. However, the statistics of the sea ice fluctuating velocity deviate from classical turbulence theory, as they show exponential instead of Gaussian distributions. Sea ice velocity and acceleration are intermittent, and both are characterized by a multifractal scaling. The oceanic and atmospheric dynamic forcing cannot explain solely the statistical properties of sea ice kinematics and dynamics. We argue that sea ice dynamic is significantly influenced by the interplay of multiple fractures that are activated intermittently within the ice pack