Nonlinear and weakly nonhydrostatic inviscid evolution of internal gravitational basin‐scale waves in a large, deep lake: Lake Constance

Abstract

The energy transfer in a large deep lake, from the largest wind‐excited basin‐scale waves down to solitary‐type waves, was investigated through a combination of inviscid nonlinear modal analysis and numerical simulations on the basis of weakly nonhydrostatic equations for internal gravitational waves. Data from four thermistor chains deployed in Lake Constance in 2003 revealed a Kelvin wave as the dominant primary basin‐scale wave that transferred its energy, through nonlinear energy cascade, to waves with smaller spatial scales. The simulation results showed that the Kelvin wave excited higher azimuthal Kelvin wave modes whose phases were locked to the parent Kelvin wave to build a steepened wave front associated with the tail of solitary‐type waves and large flow velocity in the wake of the steepened wave front. It is shown that it is the nonlinear and nonhydrostatic inviscid evolution of basin‐scale waves that shifts the flow conditions from a basinwide coherent linear flow to a flow dominated by strong currents in localized regions where damping and mixing mechanisms may act efficiently.