A treatise on frequency spectrum of drift ice velocity

概要

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Sea ice dynamics is examined for the frequency spectra of ice velocity using mathematical models and ice motion data. The data are from the Baltic Sea and Sea of Okhotsk. A general spectrum for linear coupled ice-ocean free drift is derived and analysed. Interior dynamics shows singularity in the Coriolis (inertial) frequency and asymptotic high frequency power law of -2. In the presence of internal friction the spectrum is expected to evenly fall to zero with frictional resistance increasing above yield level. In the observations, the main spectral peak is wide at the synoptic time scales. The Okhotsk Sea spectra show inertial and tidal signals but they are missing from the Baltic Sea due to very weak tides and shallow depth damping inertial oscillations. Above semidiurnal frequency ice velocity spectra fall in power law of -5/3, inherited from atmospheric and oceanic dynamics, and at very high frequencies, above 0.5 cph the fall seems to slow down to power law below -1. The Eulerian ice velocity spectrum was higher than the Lagrangian spectrum throughout the entire obtained spectrum (0.1-5 cpd). Theoretical spectra show general agreement with observations except that they have less kinetic energy at very high frequencies and much stronger inertial peak. Thus Eulerian observations are more variable than Lagrangian observations.