A treatise on frequency spectrum of drift ice velocity

• Published in: Cold regions science and technology Vol. 76-77; pp. 83 - 91
• Main Authors: Leppäranta, Matti, Oikkonen, Annu, Shirasawa, Kunio, Fukamachi, Yasushi
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-06-2012
• Subjects: Dynamics; Frequency; Kinematics; Sea ice; Spectrum; Frequency; Dynamics; Kinematics; Sea ice; Spectrum
• ISSN: 0165-232X; 1872-7441
• DOI: 10.1016/j.coldregions.2011.12.005

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 0.5cph (cycles per hour) 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 (0.1–5cpd (cycles per day)). 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.
► Analytical solution for linear coupled ice–ocean dynamics is given. ► Influences of nonlinearities in the ice velocity spectra are discussed. ► Observed very high frequency (more than one cycle per hour) spectrum is provided. ► Comparison between Eulerian and Lagrangian spectra is made based on observations. ► Comparison between theoretical and empirical spectra are presented.