Abstract

POSADA-BEDOYA, Andrés; GOMEZ-GIRALDO, Andrés  and  ROMAN-BOTERO, Ricardo. Preliminary characterization of the dominant baroclinic modes of a tropical Andean reservoir during a dry period. Rev. acad. colomb. cienc. exact. fis. nat. [online]. 2019, vol.43, n.167, pp.297-310. ISSN 0370-3908.  https://doi.org/10.18257/raccefyn.799.

Field data and a simplified numerical model were used to investigate the dominant basin-scale internal waves in a tropical Andean reservoir during a dry period. The structure and period of the observed baroclinic oscillations were inferred from spectral analysis of the measured temperature records and the associated isotherm displacements. The dominant oscillation identified from the field data had a vertical structure made of two layers with vertical velocities oscillating out of phase (V2 mode) with a period of 24 h. The theoretical baroclinic vertical modes of the reservoir were estimated by using a simplified eigenfunction model that reproduced the period and vertical structure of the observed dominant mode, indicating also that the horizontal velocity oscillations in every layer were in phase (V2H1 mode) with a period close to 24 h. The wind forcing exhibited a periodic behavior dominated by the 24-h period component and, thus, we concluded that a V2H1 mode was dominant during the survey analyzed and it was excited by resonance with the diurnal wind-forcing. We modeled the reservoir as a linear damped forced mass-spring system to estimate the damping ratio of the baroclinic oscillations and we found that the motions were underdamped with a damping rate similar to the reported in other lakes around the globe. In addition, we estimated the gradient Richardson number due to the dominant V2H1 baroclinic mode and we found that the potential diapycnal mixing by shear was low. Finally, we discuss the vertical structure of the phase of the internal wave oscillations and the potential implications of the identified internal wave field for the ecology of the reservoir. © 2019. Acad. Colomb. Cienc. Ex. Fis. Nat.

Keywords : Baroclinic modes; Internal waves; Eigenmodes; Tropical Andean reservoir.

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