Spatial structure of the dominant basin-scale internal waves in Lake Kinneret

Field data and numerical simulations were used to investigate the effects of basin shape, continuous stratification, and rotation on the three-dimensional structure of the dominant natural basin-scale internal-wave modes in Lake Kinneret, a stratified lake large enough so that the earth's rotation influences the wave motion. The structure of the modes was inferred from power spectral density of measured and simulated isotherm vertical displacements and from rotary-power spectral density of isopycnal velocities obtained from numerical simulations. The shape of the lake at the level of the thermocline, in conjunction with the dispersion relationship, determines the horizontal configuration of the natural modes. The dominant response to wind forcing was an azimuthal and vertical mode I Kelvin wave with a natural period of 22.6 h that propagated around the entire basin; the second most dominant response was a vertical mode I wave with a natural period close to 10.5 h and composed of two counter-rotating Poincare circular cells. The sloping bottom produced an intensification of vertical displacements and velocities over the slope due to focusing of waves rays after reflection at bottom slopes close to the critical angle. The amplitude of the observed oscillations was very sensitive to the phase of the wind relative to the existing waves; resonance was affected by the cessation time of the wind events because it defines the local forcing period and resets the phase of the observed oscillations.