Large Waves in Thick Interior Sakhalin Pack Ice

Results are reported describing anomalously strong waves-in-ice signals detected by a large array of bottom-moored upward-looking IPS-4 ice profilers deployed in continental shelf waters east of Sakhalin Island adjacent to Acoustic Doppler Current Profiler (ADCP) instrumentation capable of measuring ice drift velocities. Data recovered from several years of such deployments allowed identification of numerous segments of ice draft time series data containing signatures distinctive of ocean gravity waves in the interior of the seasonally southward drifting regional ice pack. Data are presented here from a time interval coincident with the passage of an intense cyclone as acquired at 8 widely-spaced monitoring stations, all initially more than 300 km from open water wave source areas. Results obtained in 9-10/10 concentrations of ice with mean drafts ranging between 1 and 2 m, showed surprisingly large concentrations of wave energy in the central portion of the monitoring array at separations no closer than about 150 km from the 5/10 ice boundary. The progress of the observed disturbances was quantified in time and space in terms of propagation speeds and directions and associated attenuation coefficients. The large deduced wave amplitudes (peak rms values > 1m) and low propagation speeds (1-2m/s) are not readily explained by conventional flexural waveor wave-scattering theories. Interpretations of the results are presented based upon modifications of the ice pack’s wave propagation properties by wind-forcing.