Energy input and dissipation in a temperate lake during the spring transition

ADCP and temperature chain measurements have been used to estimate the rate of energy input by wind stress to the water surface in the south basin of Windermere. The energy input from the atmosphere was found to increase markedly as the lake stratified in spring. The efficiency of energy transfer (Eff), defined as the ratio of the rate of working in near-surface waters (RW) to that above the lake surface (P10), increased from ∼0.0013 in vertically homogenous conditions to ∼0.0064 in the first 40 days of the stratified regime. A maximum value of Eff∼0.01 was observed when, with increasing stratification, the first mode internal seiche period decreased to match the diurnal wind period of 24 h. The increase in energy input, following the onset of stratification was reflected in enhancement of the mean depth-varying kinetic energy without a corresponding increase in wind forcing. Parallel estimates of energy dissipation in the bottom boundary layer, based on determination of the structure function show that it accounts for ∼15% of RW in stratified conditions. The evolution of stratification in the lake conforms to a heating stirring model which indicates that mixing accounts for ∼21% of RW. Taken together, these estimates of key energetic parameters point the way to the development of full energy budgets for lakes and shallow seas

The seasonal hydrodynamic habitat

© Springer Science+Business Media Dordrecht 2014. In this chapter, we present a detailed analysis of the annual thermal regime of Lake Kinneret based on high-resolution thermistor chain and meteorological data collected by the Centre for Water Research at the University of Western Australia during the period April 2007–April 2008. Five seasonal regimes of the yearly cycle are defined to illustrate the main physical aspects of the lake hydrodynamics and their effects on ecological processes

Quantifying the effect of wind on internal wave resonance in Lake Villarrica, Chile

Artículo de publicación ISILake Villarrica, located in south central Chile, has amaximum depth of 167mand amaximum fetch of about 20 km.The lake is monomictic, with a seasonal thermocline located at a depth of approximately 20 m. Field data show the presence of basin-scale internal waves that are forced by daily winds and affected by Coriolis acceleration. A modal linear and nonlinear analysis of internal waves has been used, assuming a two-layer system. The numerical simulations show good agreement with the internal wave field observations. The obtained modes were used to study the energy dissipation within the system, which is necessary to control the amplitude growth. Field data and numerical simulations identify (1) the occurrence of a horizontal mode 1 Kelvin wave, with a period of about a day that coincides with the frequency of daily winds, suggesting that this mode of the Kelvin waves is in a resonant state (subject to damping and controlled by frictional effects in the field) and (2) the presence of higher-frequency internal waves, which are excited by non-linear interactions between basinscale internal waves. The non-linear simulation indicates that only 10% of the dissipation rate of the Kelvin wave is because of bottom friction, while the rest 90% represents the energy that is radiated from the Kelvin wave to other modes. Also, this study shows that modes with periods between 5 and 8 h are excited by non-linear interactions between the fundamental Kelvin wave and horizontal Poincaré-type waves. A laboratory study of the resonant interaction between a periodic forcing and the internal wave field response has also been performed, confirming the resonance for the horizontal mode 1 Kelvin wave.The authors acknowledge support of the Civil Engineering Department, Universidad de Chile, FONDECYT Project 1080617 and the Civil Engineering Department, University of Dundee. The first author acknowledges financial support from Department of Graduate and Postgraduate Degree, Universidad de Chile