Decoupled basin-scale internal waves in a continuously stratified two-basin tropical Andean reservoir

Abstract

Field measurements and numerical modeling were used to characterize the decoupled basin-scale internal waves of the two-basin La Fe reservoir, during a typical dry period of weak, continuous, and wide metalimnion stratification. The structure and period of the baroclinic oscillations were obtained by wavelet analysis of measured and modeled temperature and isotherm displacements. The numerical modeling showed that sub-basins of La Fe oscillate decoupled, with dominant H1 modes of different vertical order excited in each basin. The periodic wind forcing in La Fe transfers energy to internal waves at the forcing frequency as well as its harmonics, such that the energy partitioning between frequencies in the wind is different from the one in the internal wave field. Supported by numerical experiments, we show that oscillations in La Fe are dominated by decoupled modes swinging in the EW direction, with high amplitude within one basin, and minimum amplitude in the other, which makes it possible to observe motions with the same frequency but different vertical order in each basin. The morphometry of each basin provides the physical dimensions required to meet the dispersion relationship for a stratification and frequency of the excited mode, regardless of the shape of the entire lake. Because of the EW alignment of the decoupled modes, the transversal EW setup of internal waves by the wind is the main factor for their excitation.