Geoscience Reference
In-Depth Information
10
Internal Waves in Laboratory Experiments
Bruce Sutherland
1
, Thierry Dauxois
2
, and Thomas Peacock
3
10.1. INTRODUCTION
and Keady
, 1997]. Even with such simple geometries and
despite neglecting Coriolis effects, this work has revealed
the importance of including viscosity to resolve singular-
ities that occur along tangents to the oscillating body in
the along-beam direction.
More recently, in the study of tidally generated internal
waves, attention has turned to faster time-scale processes
in which large-amplitude internal wave packets are gener-
ated during one cycle of the tide. This work extends earlier
studies of steady uniformly stratified flow over topog-
raphy (e.g., see
Baines
[1995]) to include consideration
of nonuniform stratification and large-amplitude topog-
raphy. Oceanographers have focused primarily upon the
generation, propagation, and dissipation of internal soli-
tary waves at the thermocline [
Pinkel
, 2000;
Klymak and
Gregg
, 2004;
Klymak et al.
, 2006;
Li and Farmer
, 2011;
Alford et al.
, 2011].
By exploring large-amplitude and viscous effects, the
results of laboratory experiments have often challenged
existing theory. For example, they have revealed the
importance of nonlinear processes in the scattering of
internal waves from large-amplitude topography [
Peacock
etal.
, 2009], they have demonstrated the importance of the
viscous boundary layer in the generation of internal waves
from oscillating bodies [
Sutherland and Linden
, 2002;
Flynn et al.
, 2003], and they have shown that boundary
layer separation in stratified flow over steep topography
reduces the effective topographic height while generat-
ing turbulence and internal waves in the lee of localized
topography [
Baines and Hoinka
, 1985;
Sutherland
, 2002;
Aguilar and Sutherland
, 2006].
Laboratory experiments have entered a renaissance due
to digitization technology, advancement in lasers and
computer-controlled equipment, and increases in compu-
tational memory and speed, which have created valuable
new analysis tools such as particle image velocimetry
(PIV) and laser-induced fluorescence (LIF). As a result,
Since the realization by physical oceanographers that
transport and mixing by internal waves are an impor-
tant component of the thermohaline circulation, there
has been a resurgence in interest in their dynamics [
Polzin
et al.
, 1997;
Munk and Wunsch
, 1998;
Ledwell et al.
, 2000].
Consequent studies have been designed to examine mech-
anisms for wave generation and interaction with topog-
raphy. Theoretical studies have examined the means by
which energy from the moon forcing the barotropic tide
might be converted into internal wave energy as a conse-
quence of oscillatory stratified flow over topography. This
began with the pioneering studies of
Zeilon
[1912] and
Baines
[1974, 1982] and have since been extended, though
still in the realm of linear theory, to examine the influence
of more complex topography and stratification [
Balm-
forth et al.
, 2002;
Llewellyn-SmithandYoung
, 2002;
Bühler
and Muller
, 2007]. Related to these is the examination
of scattering of internal waves by topography in which
incident low-mode internal waves generate an oscillatory
flow over topography that launches higher-mode internal
waves [
Larsen
, 1969;
Robinson
, 1969;
Sandstrom
, 1969].
Just as an oscillatory flow over a rigid body gener-
ates internal waves, so does an oscillating body generate
internal waves in otherwise stationary fluid. The partic-
ular circumstance of internal waves generated by oscil-
lating cylinders and spheres has garnered much attention
[
Görtler
, 1943;
Mowbray and Rarity
, 1967;
Thomas and
Stevenson
, 1972;
Voisin
, 1991, 1994;
Hurley
, 1997;
Hurley
1
Departments of Physics and of Earth & Atmospheric
Sciences, University of Alberta, Edmonton, Alberta, Canada.
2
Laboratoire de Physique, École Normale Supérieure, Lyon,
France.
3
Department of Mechanical Engineering, Massachusetts
Institute of Technology, Cambridge, Massachusetts, United
States of America.
