Publication

Observations of mixing near the sides of a deep lake in winter

Ulrich Lemmin
2002
Journal paper
Abstract

The dissipation rate of turbulent kinetic energy per unit mass, epsilon, vertical eddy diffusivity, K-z, and the rate of dissipation of temperature variance, X, are estimated over the sloping sides of Lake Geneva both far from and near the bed, using temperature data from horizontal tracks of a submarine during periods of winter cooling. The estimated values are about one order of magnitude greater near the slope than those distant from it. The mean dissipation rate per unit mass averaged over the epilimnion varies between O(10(-10)) m(2) s(-3) in calm weather to O(10(-8)) m(2) s(-3) in winds of 8 m s(-1), for surface buoyancy fluxes of 6 x 10(-9) m(2) s(-3) and 1.1 x 10(-8) m(2) s(-3), whereas near the slope e has an average value of 3 x 10(-8) m(2) s(-3). The relation between K-2 and epsilonN(-2) (where N is the buoyancy frequency) is examined. Values of the mixing efficiency, Gamma = epsilonN(-2)K(z)(-t), of 0.15 +/- 0.1 and 0.16 +/- 0.1 are obtained in the upper 10-m layer for calm and windy conditions, respectively. Near the slope, Gamma is found to be 0.22 +/- 0.2, slightly larger than in surface layers under windy conditions. Different mixing mechanisms in different regions, near the slope and in the surface waters of the epilimnion and relatively calm deeper layers, can be identified in the diagram of overturn Froude number versus overturn Reynolds number. Mixing near the slope in the epilimnion appears to be related to the gravitational winter cascading of cold water down the sloping sides of the lake.

About this result
This page is automatically generated and may contain information that is not correct, complete, up-to-date, or relevant to your search query. The same applies to every other page on this website. Please make sure to verify the information with EPFL's official sources.
Related concepts (40)
Lake stratification
Lake stratification is the tendency of lakes to form separate and distinct thermal layers during warm weather. Typically stratified lakes show three distinct layers: the epilimnion, comprising the top warm layer; the thermocline (or metalimnion), the middle layer, whose depth may change throughout the day; and the colder hypolimnion, extending to the floor of the lake. Every lake has a set mixing regime that is influenced by lake morphometry and environmental conditions.
Lake
A lake is a naturally occurring, relatively large body of water localized in a basin surrounded by dry land. A lake generally has a slower-moving flow than the inflow or outflow stream(s) that serve to feed or drain it. Lakes lie completely on land and are separate from the ocean, although, like the much larger oceans, they form part of the Earth's water cycle by serving as large standing pools of storage water. Most lakes are freshwater and account for almost all the world's surface freshwater, but some are salt lakes with salinities even higher than that of seawater.
Winter
Winter is the coldest season of the year in polar and temperate climates. It occurs after autumn and before spring. The tilt of Earth's axis causes seasons; winter occurs when a hemisphere is oriented away from the Sun. Different cultures define different dates as the start of winter, and some use a definition based on weather. When it is winter in the Northern Hemisphere, it is summer in the Southern Hemisphere, and vice versa. In many regions, winter brings snow and freezing temperatures.
Show more
Related publications (48)

Shafranov shift correction to the Furth-Yoshikawa scaling of tokamak adiabatic compression

Olivier Sauter

In 1970, Furth and Yoshikawa (1970 Phys. Fluids 13 2593-6) introduced the scalings of adiabatic plasma compression. Basically, if the shape of the external plasma boundary and the aspect ratio are preserved during the compression, then the density, kinetic ...
IOP Publishing Ltd2023

Chimney‐Like Intense Pelagic Upwelling in the Center of Basin‐Scale Cyclonic Gyres in Large Lake Geneva

David Andrew Barry, Ulrich Lemmin, Seyed Mahmood Hamze Ziabari, Rafael Sebastian Reiss, Mehrshad Foroughan

Basin-scale quasi-geostrophic gyres are common features of large lakes subject to Coriolis force. Cyclonic gyres are often characterized by dome-shaped thermoclines that form due to pelagic upwelling that takes place in their center. At present, the dynami ...
2023

Detecting submesoscale cold filaments in a basin-scale gyre in large, deep Lake Geneva (Switzerland/France)

David Andrew Barry, Ulrich Lemmin, Seyed Mahmood Hamze Ziabari, Amir Mehdi Razmi

Submesoscale filaments are a well-documented feature of oceanic flow fields. Based on the analysis of high-resolution 3D numerical simulations, field observations and remote sensing imagery, this study, carried out in Lake Geneva, Western Europe's largest ...
2022
Show more
Related MOOCs (7)
Advanced statistical physics
We explore statistical physics in both classical and open quantum systems. Additionally, we will cover probabilistic data analysis that is extremely useful in many applications.
Advanced statistical physics
We explore statistical physics in both classical and open quantum systems. Additionally, we will cover probabilistic data analysis that is extremely useful in many applications.
Geographical Information Systems 1
Organisé en deux parties, ce cours présente les bases théoriques et pratiques des systèmes d’information géographique, ne nécessitant pas de connaissances préalables en informatique. En suivant cette
Show more