High‐frequency internal waves in the littoral zone of a large lake

Abstract

Observations in the littoral zone of a large lake (Lake Constance) revealed strong and periodic fluctuations of temperature and current velocity on timescales between 10 and 15 min associated with high‐frequency internal waves. The peak in the spectral energy of the current velocity fluctuations associated with high‐frequency internal waves follows the seasonal dynamics of stratification, described by the stability frequency N. A comparison between the nearshore current velocity measurements in the littoral zone with temperature measurements in the pelagic of Lake Constance revealed a strong coupling between the occurrence of high‐frequency internal waves in the littoral zone and the passage of the basin‐scale internal Kelvin wave with a period of about 4 d.

Opposing diel migration of fish and zooplankton in the littoral zone of a large lake

“…3a by the temperatures measured at 8 m and 4 m depth, is mainly characterized by a strong wind event on September 18, 2005 with wind speeds of up to 12 m s -1 . Before this wind event, both thermistors were within the seasonal thermocline and showed strong temperature fluctuations of up to 10°C on time scales of minutes to hours, which were caused by internal waves (Lorke et al, 2006). Wind-induced mixing resulted in a deepening of the surface mixed layer, such that the thermocline was below the depth of measurement.…”

Degeneration of internal Kelvin waves in a continuous two-layer stratification

“…Field studies in stratified medium or large lakes have identified important sources of turbulence in the density interface attributed to shear instabilities (Kelvin-Helmholtz-type billows) riding over the slope of IKWs (Lorke 2007;Preusse et al 2010). Furthermore, density inversion and interfacial breakings at the trough of a solitary wave train of large amplitudes have also been associated with the nonlinear degeneration of basin-scale IKWs (Preusse et al 2010(Preusse et al , 2012a.…”

“…(a) t/T k = 0, (b) t/T k = 0.128, (c) t/T k = 0.25, (d) t/T k = 0.5, (e) t/T k = 0.75, (f ) t/T k = 1.0, (g) t/T k = 1.5, (h) t/T k = 1.75, (i) t/T k = 2.0, (j) t/T k = 2.25, (k) t/T k = 2.75, (l) t/T k = 3.0.The first three regimes have been analysed in previous numerical(de la Fuente et al 2008;Sakai & Redekopp 2010) and experimental studies(Wake, Ivey & Imberger 2005;Ulloa et al 2014), whereas the TR on IKWs has been observed only in field data(Lorke 2007;Preusse et al 2010) and to date in numerical experiments.…”

“…Field measurements have shown that the passage of internal Kelvin waves (IKWs) is correlated with high-frequency internal waves (Boegman et al 2003;Lorke, Peeters & Bäuerle 2006;de la Fuente et al 2010), shear instabilities and local overturns near the wave troughs in the near-shore regions (Preusse, Peeters & Lorke 2010;Preusse, Freistühler & Peeters 2012a). These processes lead to significant localized turbulence and mixing in the pelagic thermocline (Lorke 2007;Bouffard & Lemmin 2013). Over the course of the stratified season, dynamical changes in the wave regime can alter the spatial and temporal distribution of turbulent activity induced by Kelvin waves.…”

Physical controls on the spatial evolution of a dinoflagellate bloom in a large lake

“…The primary result of this work that the bloom evolution into the center of the lake was controlled by physical processes and could be equally derived from normalized (uncalibrated) images because the relative concentrations returned from within an image are generally consistent. The seasonal evolution of wind and internal wave fields has been documented in many lakes (Lorke et al 2006;Mortimer 2006;Vidal et al 2007), and so the processes leading to bloom evolution are potentially similar in many systems. Future work will focus on the role of algal species in determining spatial patterns, and, in particular, the way in which the vertical migration capability of some species affects spatial variability (Hunter et al 2008).…”