ICE MOTIONS FORCED BY BOUNDARY-LAYER TURBULENCE

The motions of ice on frozen oceans in the frequency band from 0.05 to 10.0 s-1 have typically been associated with surface gravity waves which were generated by distant storms in the open ocean and which then propagate into the ice. Evidence relating these motions to local wind forcing has been less direct. Data on ice motions have been obtained with tilt meters on a land-locked, frozen lake, and the motions are shown to be directly related to forcing by the local wind. The variance of ice surface tilt increased by more than 3 orders of magnitude when the mean wind speed increased by a factor of less than 2, even when the wind speed remained below the minimum phase speed for freely propagating waves. A model is presented in which ice motions result from an interaction between turbulent eddies in the atmosphere and the ice surface. Model predictions are shown to be consistent with the lake observations.