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

Abstract

Observations of the internal wave field using thermistor chains in Lake Kinneret (Israel) showed a substantial energy peak at frequencies just below the maximum buoyancy frequency. The waves were of the first vertical mode, occurred in groups, and resulted in isotherm displacements of up to 4 m in 22 m of water. The appearance of this high-frequency internal wave energy was 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 energy observed under the same wind conditions when the metalimnion was closer to the surface. The relationship of the high-frequency waves to the wind and the basin-scale internal waves implies a generation mechanism associated with shear in the surface layer (observed to be approximately 0.08 s-1), similar to that responsible for generating high-frequency internal waves in the equatorial Pacific. A linear stability analysis of the mean state during periods of high-frequency wave activity revealed the existence of unstable modes, whose period and frequency bandwidth closely matched field observations. Copyright 2001 by the American Geophysical Union.