Internal waves in JASIN

Abstract

The internal wavefield during the Joint Air—Sea Interaction (JASIN) experiment was monitored by moored current meters and moored and towed thermistor chains. The observations were concentrated in the upper ocean near the centre of Rockall Trough, but velocity measurements were also made near topographic features and throughout the water column. Observed spectra are compared with results from the deep ocean, as represented by the Garrett-Munk (GM) model of the spectral continuum, and are generally found to have spectral levels equal to or greater than the GM spectrum. The greatest deviation from the GM spectrum occurs at high frequencies and wavenumbers where the observed spectra often exhibit a spectral shoulder and high vertical coherence. These features, also found in other upper-ocean spectra, are explained by a model composed of three vertically standing modes. The spatial variation of internal wave variance is related to topography: variance is highest near rough topography. The ratio of variance in the semidiurnal tidal band to variance in a band in the continuum is approximately constant. The possibility of a dynamical link between the two frequency bands requires further investigation. The semidiurnal internal tide varies temporally and spatially. Rockall Bank is identified as the source of an energetic beam of tidal oscillations during a one-week period.