Evolution of internal waves in a rotating, stratified lakeforced by wind. Field observations and numericalsimulations in Lake Villarrica, Chile

摘要

Lake Villarrica, located in south central Chile, has a maximum depth of 167 m and amaximum fetch of about 20 km. The lake is monomictic, with a seasonal thermoclinelocated at a depth of about 20 m. In this paper, results of a field study and numericalsimulations of the response of the lake to wind are presented and discussed, focusingon the modal analysis of internal waves affected by Coriolis effects. The field datashowed forced and free responses of the lake stratification in the form of tilting of theisopycnals and the presence of linear and nonlinear internal waves. A thermocline isidentified, assuming a two-layer stratification of the system, which shows dominantfrequencies of oscillation, corresponding to periods of 9, 11, 12.4, 18.2, 21.9, 26.9and 103 hours. Most of these frequencies are also predicted by the numericalsimulations, which show a reasonably good agreement with observed internal waves.The numerical simulations identify the occurrence of a mode 1 Kelvin wave, with aperiod of about a day that coincides with the frequency of daily winds blowing on thelake. The simulations suggest that this mode of the Kelvin waves would be in a quasi-resonant state, which in the field would be damped and controlled by friction effects.