Sea ice motion in response to geostrophic winds

It is an old rule‐of‐thumb that sea ice moves with a speed of about 2% of the surface wind and about 45° to the right of the wind. A similar relationship between the ice velocity and the geostrophic wind is examined here. It is found that only about half of the long‐term (several month) average ice motion is directly related to the geostrophic wind, the other half being due to the mean ocean circulation. On shorter time scales and in all seasons, more than 70% of the variance of the ice velocity in the central Arctic Ocean is explained by the geostrophic wind. Within about 400 km of the coasts the geostrophic wind is less successful in explaining the ice motion. The spatial variations in ice velocity are also partly explained by the geostrophic wind. About half of the variance in the large‐scale ice vorticity and shear are accounted for. On the other hand, none of the large‐scale ice divergence can be explained by the wind. The long‐term average ocean current is estimated by subtracting the share of the ice motion caused by the wind from the total ice motion.