INTERNAL WAVE DIRECTIONAL SPECTRA USING AN ACOUSTIC DOPPLER CURRENT PROFILER

An acoustic Doppler current profiler was deployed through land-fast ic e near Resolute, Northwest Territories. It recorded a distinct train o f high-frequency (periods < 20.0 min) internal waves lasting 10 hours. Assuming linear dynamics, a modal decomposition of the three velocity channels led to the modal pressure anomaly taking a role analogous to that of the surface displacement sensed by a surface following heave, pitch, and roll buoy. Partitioning the data into frequency dependent cross-spectral matrices of the modal horizontal pressure anomaly enabl ed the computation of high-resolution, data-adaptive directional spect ra, recently presented for use with surface gravity waves. The mode 1 directional spectra were particularly sharp and indicated a cross-chan nel point of origin of the waves to the northeast of the study site. T he lowest two frequency bands contained considerable spectral power de nsity that could not be accurately described by the modal decompositio n. A direct examination of the cross-channel velocity time series indi cated substantial low-frequency (periods > 30.0 min) horizontal flow w ithout a corresponding coherent vertical velocity component, attribute d to a density driven along-isopycnal flow created by salt rejection e manating from a broad shelf to the northeast.