Internal tides in the Bay of Biscay: conversion rates and seasonal effects

Internal tides in the Bay of Biscay are studied using a numerical linear hydrostatic internal-tide generation model, in which along-slope uniformity is assumed. The focus is on the seasonal changes in the generation and dynamics. The results are compared with observations made near the shelf-break in early summer. They were obtained using a towed Acoustic Doppler Current Profiler (ADCP) on repeated tracks in the Bay of Biscay; this provides a synoptic view in a plane spanned by the vertical and the cross-slope direction. In the reproduction of the observed patterns by the numerical model, the presence of the seasonal thermocline turns out to be essential. However, the model results also indicate that its presence has only a minor effect on the integrated conversion rate (which is about 10 kW/m). The main region of generation lies deep and is seasonally independent; the presence of the deep permanent pycnocline does increase the integrated conversion rate strongly, by a factor two.