On internal waves near the high-frequency limit in an enclosed basin

Observations of the internal wave field using thermistor chains in Lake Kin neret (Israel) showed a substantial energy peak at frequencies just below t he maximum buoyancy frequency. The waves were of the first vertical mode, o ccurred in groups, and resulted in isotherm displacements of up to 4 m in 2 2 m of water: The appearance of this high-frequency internal wave energy wa s closely related to the strength of the wind field, A weaker relationship was found with the phase of the basin-scale internal waves, with more energ y observed under the same wind conditions when the metalimnion was closer t o the surface. The relationship of the high-frequency waves to the wind and the basin-scale internal waves implies a generation mechanism associated w ith shear in the surface layer (observed to be approximately 0.08 s(-1)), s imilar to that responsible for generating high-frequency internal waves in the equatorial Pacific. A linear stability analysis of the mean state durin g periods of high-frequency wave activity revealed the existence of unstabl e modes; whose period and frequency bandwidth closely matched field observa tions.