Horizontal structure and excitation of primary motions in a strongly stratified lake

Abstract

A modal analysis in the horizontal plane was extended to a layer-stratified basin with irregular bathymetry, and the theory was applied to Lake Biwa to investigate the horizontal structure and excitation of the basin-scale internal waves and gyres. The horizontal structure of the basin-scale internal waves consisted of cyclonic and anticyclonic elliptic cells, each of which appeared to follow the dispersion relationship of Kelvin and Poincaré waves in elliptic basins. The internal waves were preferentially excited depending on the arrangement of the cells and the wind direction, but the spatial distribution of wind stress curl over the lake primarily determined the horizontal structure of the ensuing gyres. Decoupled evolutionary equations for the individual modes provided a good approximation for excitation of the internal waves and early stages of excitation of the gyres before nonlinear effects and damping become significant. The modal decomposition of hydrodynamic simulation results also showed that the primary action of the wind was to excite the internal waves; however, these internal waves were damped within a few days, and the dynamics during calm periods were dominated by the gyres, illustrating the importance of internal waves on mixing and gyres on long-term horizontal transport.

The evolution of internal waves in a rotating, stratified, circular basin and the influence of weakly nonlinear and nonhydrostatic accelerations

“…For a particular basin geometry, horizontal modes can be decomposed into multiple fundamental modes oscillating in harmony side by side (Gó mez-Giraldo et al 2006). In simple terms, those modes are excited that match the spatial and temporal distribution of the imposed wind stress (Csanady 1973;Gó mez-Giraldo et al 2006;Shimizu et al 2007).…”

Evaluation of Thermal Stratification and Flow Field Reproduced by a Three-Dimensional Hydrodynamic Model in Lake Biwa, Japan

“…According to the research about Lake Kinneret (Israel), internal waves play a significant part in the transportation of materials in the bottom boundary layer [13]. Internal waves have also been studied in Lake Biwa by field observation [14], modal analysis [15], and numerical simulation [16,17]. Kitazawa et al [18] showed that internal waves would affect the transportation of hypoxic waters in the bottom boundary layer.…”

Summer thermal structure and anticyclonic circulation of Lake Erie

“…[6] While cyclonic circulations are abundant in lakes and marginal seas [Emery and Csanady, 1973;Laval et al, 2005;Beletsky and Schwab, 2008], anticyclonic motions rarely dominate basin-scale circulation [Strub and Powell, 1986] and appear primarily as regional gyres [Beletsky et al, 1999;Rueda et al, 2005;Shimizu et al, 2007]. Even more rare are observations of thermocline depressions linked to anticyclonic gyres [Endoh and Okumura, 1993].…”