Geoscience Reference
In-Depth Information
7
Laboratory Experiments on Flows Over Bottom Topography
Luis Zavala Sansón
1
and Gert-Jan van Heijst
2
7.1. INTRODUCTION
slope in a rotating tank simulates the planetary
β
-effect
(the latitudinal gradient of the Coriolis parameter [see,
e.g.,
van Heijst
, 1994]. Using this effect, it is possible to
study the self-propagation mechanism of monopolar vor-
tices in the laboratory. The drift of vortices under the
β
-plane approximation is characteristic of mesoscale
eddies in the ocean (see
Vukovich
[2007] for loop cur-
rent eddies in the Gulf of Mexico) and in the atmosphere
(e.g.,
Chan
[2005] for tropical cyclones). During their
drift, vortices may encounter topographic features that
modify their structure or trajectory [see, e.g.,
Zehnder
,
1993;
de Steur and van Leeuwen
, 2009]. Another impor-
tant topic is the vertical advection of chemical and bio-
logical material due to mesoscale features in the ocean.
Several mechanisms introducing or extracting nutrients
into/from the upper ocean surface have been recently dis-
cussed by several authors [
Lévy
, 2008], and in particular
due to topographic effects [
Genin
, 2004]. Some other rel-
evant geophysical phenomena over topography, such as
the propagation of topographic Rossby waves, the self-
organization properties of quasi-two-dimensional turbu-
lence, and the dynamics of shallow flows, can be further
studied by means of laboratory experiments.
Previous reviews discussing flow-topography phenom-
ena are the studies of
Hopfinger and van Heijst
[1993],
Boyer and Davies
[2000], and
van Heijst and Clercx
[2009].
Those works provide a modern and complete description
of several flows subject to different topographic scenarios.
They also describe the similarity parameters that provide
a physical justification to compare experimental results
with oceanographic or atmospheric observations as well
as a review of different experimental methods for flow
measurement and visualization. A classical reference to
the dynamics of rotating lows is the topic of
Greenspan
[1968].
In Section 7.2 we briefly review some typical charac-
teristics of the modeling of geophysical flows in rotating
fluid containers as well as some aspects of (nonrotating)
The motions of mesoscale and large-scale geophysical
flows in the oceans and the atmosphere (with sizes of the
order of tens to hundreds of kilometers) are essentially
affected by Earth's rotation. At these scales geophysical
flows can be also strongly influenced by bottom topog-
raphy. Thus, the essential dynamical ingredients to be
discussed here are topography effects in a rotating sys-
tem. More specifically, we shall present recent experimen-
tal studies on homogeneous flows simulating geophysical
situations, in which the dynamics are dominated by the
combination of rotation and topography. We will also
discuss the two-dimensionality of shallow, nonrotating
fluid systems. The presentation and discussion of the topic
are based on the physical scales of different experimen-
tal facilities, in a similar vein to the study of
von Arx
[1957]. In contrast with that study, we focus the discussion
on numerous examples that underline the role of topog-
raphy effects in laboratory experiments with horizontal
scales
L
ranging from some centimeters to a few meters
and vertical scales
H
from some milimeters to about 1 m.
In addition, we ignore stratification effects, gravity waves,
and, to a great extent, free surface effects. It will be shown
that laboratory experiments performed in large containers
are useful to study rather different problems than those
performed within containers with smaller dimensions. In
other words, we aim at pointing out advantages and dis-
advantages of experiments performed within the available
range of length scales in typical laboratories.
Several examples presented in subsequent sections
address specific oceanographic or atmospheric problems.
For instance, the presence of a weak, linear topographic
1
Departamento de Oceanografía Física, CICESE, Ensenada,
Baja California, México.
2
Department of Applied Physics, Eindhoven University of
Technology, Eindhoven, The Netherlands.
