Sea-Ice Drift on the Northeastern Shelf of Sakhalin Island

Abstract

Ice-drift velocity records from coastal radar stations, combined with data from moored current meters and coastal wind stations, are used to examine sea-ice motion off the northeastern coast of Sakhalin Island in the Sea of Okhotsk. Ice motion is shown to be governed primarily by diurnal tidal currents and wind-induced drift, which explain 92%–95% of the total ice-drift variance. Diurnal tidal motions predominate off the northern Sakhalin coast, accounting for 65%–80% of the variance, while low-frequency wind-induced motions prevail off the south-central coast, accounting for over 91% of the ice-drift variance. Maximum diurnal tidal ice-drift velocities range from 90–110 cm s−1 on the north coast to 10–15 cm s−1 on the south coast, in good agreement with the barotropic model of Kowalik and Polyakov. The presence of diurnal shelf waves accounts for the strong diurnal currents on the steeply sloping northern Sakhalin shelf, while the absence of such waves explains the weak diurnal currents on the more gently sloping south-central shelf. Using a vector regression model, the authors show that wind-induced ice-drift “response ellipses” (the current velocity response to a unity wind-velocity forcing) are consistent with a predominantly alongshore response to the wind, with wind-induced currents most pronounced off the south-central coast where water depths are relatively shallow. Time–frequency analysis of wind and ice-drift series reveals that, in winter, when sea ice is most extensive and internally cohesive, the ice response is almost entirely aligned with the alongshore component of the wind; in spring, when sea ice is broken and patchy, the ice responds to both the cross- and alongshore components of the wind.

Enhancement of Sea Ice Drift due to the Dynamical Interaction between Sea Ice and a Coastal Ocean

“…Mizuta et al (2005) showed that CTWs are induced by alongshore wind stress in the Sakhalin coast even in the sea ice season. Under the realistic depth profile and stratification off the Sakhalin coast, located in relatively high latitudes (468-558N), the CTWs have nearly barotropic structure (Shevchenko et al 2004;Mizuta et al 2005;Ono et al 2006). In addition, from the dispersion relations, the waves with the period of ;10 days can be treated as long waves.…”

“…The spectral density of the wind decreases monotonically without any specific peak (not shown). We arbitrarily choose 0.1 cpd as a representative of low frequency and its wind speed is set to jÛ a j 5 7 m s prominent off the Sakhalin coast (Shevchenko et al 2004). The spatial distribution of g for the case of 0.1 cpd is shown in Fig.…”

A treatise on frequency spectrum of drift ice velocity

“…Eulerian data have also been analysed (e.g., Schevchenko et al, 2004) In the observations, Eulerian spectrum is at higher level than the Lagrangian spectrum as anticipated. The difference does not show significant variations across the spectrum, but the slopes of the spectra show indication to differ at high frequencies.…”

“…Many observation programmes have been performed on sea ice kinematics, and, consequently a number of papers have been published on ice velocity time series analyses (e.g., Hibler et al, 1974;Ono, 1978;McPhee, 1980;Thorndike and Colony, 1980;Leppäranta, 1981;Hutchings and Hibler, 2002;Schevchenko et al, 2004;Geiger and Perovich, 2008). Here ice motion data from two different kinds of basins are used to extend the empirical knowledge toward higher frequencies and to compare the observed spectra of ideal models.…”

“…A particular problem is scaling of sea ice dynamics and its space-time spectrum. Temporal characteristics of ice drift have been treated in papers about drifter data (e.g., Hibler et al, 1974;Ono, 1978;Thorndike and Colony, 1980;McPhee, 1980;Leppäranta, 1981;Leppäranta and Omstedt, 1990;Schevchenko et al, 2004;, where the close connection with wind and the presence of Coriolis and tidal signals have been recognised. Inertia of the ice itself shows up only at very high frequencies.…”