Earth rotation effects on the internal wave field in a stratified small lake: Numerical simulations

The Princeton Ocean Model was applied to the Sau Reservoir, a medium-sized Mediterranean reservoir (5.7 km2) located in Catalonia, Spain, during the summer season, when the water column is continuously stratified and forced by a breeze regime with velocities of up to 3-4 m/s. Based on our simulations, the internal wave field has been analysed and the numerical results compared with the field data previously analysed by other authors. The model adequately reproduces all the significant modes observed. The simulations show the importance of rotational modes on the internal wave field. The Burger number S for all rotating internal waves is on the order of 10−1, and the internal Rossby radius R is on the order of 102 m, that is, smaller than the width of the lacustrine area of the reservoir (103 m). Specifically, two rotating third vertical modes were found during the analysed period: the first, a 24-hour period, was forced by the wind and the phase rotated clockwise; and the second, a 12-hour period, can be interpreted as a second azimuthal horitzontal mode of a Poincaré wave. A second vertical mode of 8 hours was observed to rotate counter clockwise, although in this case the Earth’s rotation appears not to have been of importance because the same results could be obtained without taking into account the Coriolis force. Finally, two first vertical modes, one of 6 hours and the other of 5 hours, were observed, although with no rotational behaviour. These modes correspond, respectively, to the first and second horizontal stationary modes. Further analysis of the simulated velocities shows the existence of a net clockwise flow along the shore as a consequence of the dominant mode of 24 hours, with a mean velocity of 0.5 m/s that reverses at a distance of about 300 m from the coast. Preliminary results based on the simulated velocity field predict horizontal trajectories of passive particles of up to 1 km per day and vertical displacements of up to 5 m across the entire water column ​
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