Effect of wind variability on topographic waves: Lake Kinneret case

We studied the winter wind driven circulation in Lake Kinneret (northern Israel) using state of the art atmospheric (Regional Atmosphere Modeling System (RAMS)) and oceanic (Regional Ocean Modeling System (ROMS)) general circulation models. During winter the lake is completely mixed and mainly forced by the passage of synoptic weather systems. The lake's dynamic response was identified using various wind regimes. The response of the lake to a uniform wind stress resulted in the formation of a double-gyre circulation pattern. After removal of the wind stress, the double-gyre pattern slowly rotated cyclonically (with a time period of several days) around the lake perimeter, consistent with the pattern of the lowest-mode basin-scale topographic (vorticity) wave. The use of RAMS-simulated wind fields resulted in a less symmetric structure of the double-gyre pattern due to the presence of a curl in the wind field. Using various wind regimes to force the lake indicated that the presence of a positive or negative curl in the wind field might result in a shift in the topographic wave frequency to a higher or lower value, respectively. This result may be easily applied to motions on the geophysical scale. The currents predicted by RAMS-ROMS agree well with measured data near the center of the lake. Forcing the model with a spatially uniform wind field constructed from a single station resulted in poor agreement with the observed currents, indicating the importance of the wind field spatial pattern.