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experiment was ever constructed). However, following the
development of the electronic computer during the first
half of the twentieth century and
Richardson's
[1922] pio-
neering work on numerical weather prediction, these more
complex laboratory representations of the atmosphere
were superseded.
The later experiments of
Exner
[1923] explored a dif-
ferent regime in which baroclinic instability seems to have
been present. The flows he demonstrated were evidently
quite disordered and irregular, likely due in part to the
parameter regime he was working in but also perhaps
because of inadequate control of the key parameters. It
was not until the late 1940s, however, that Fultz began
a systematic series of experiments at the University of
Chicago on rotating fluids subject to horizontal differen-
tial heating in an open cylinder (hence resulting in the
obsolete term “dishpan experiment”) and set the subject
onto a firm footing. Independently and around the same
time,
Hide
[1958] began his first series of experiments at
the University of Cambridge on flows in a heated rotating
annulus, initially in the context of fluid motions in Earth's
liquid core. By carrying out an extensive and detailed
exploration of their respective parameter spaces, both of
these pioneering studies effectively laid the foundations
for a huge amount of subsequent work on elucidating
the nature of the various circulation regimes identified
by Fultz and Hide, subsequently establishing their bifur-
cations and routes to chaotic behavior, developing new
methods of modeling the flows using numerical tech-
niques, and measuring them using ever more sophisticated
methods, especially via multiple arrays of in situ probes
and optical techniques that exert minimal perturbations
to the flow itself.
An important aspect of the studies by Fultz and Hide
was their overall agreement in terms of robustly identi-
fying many of the key classes of circulation regimes and
locating them within a dimensionless parameter space. A
notable exception to this, at least in early work, was the
lack of a regular wave regime in Fultz's open cylinder
experiments, in sharp contrast to the clear demonstration
of such a regime in Hide's annulus. As further discussed
below, this led to some initial suggestions [
Davies
, 1959]
that the existence of this regime was somehow depen-
dent on having a rigid inner cylinder bounding the flow
near the rotation axis. This was subsequently shown not
to be the case in open cylinder experiments by Fultz
himself [
Spence and Fultz
, 1977] and by Hide and his
co-workers [
HideandMason
, 1970;
BastinandRead
, 1998]
and two-layer [
Hart
, 1972, 1985] experiments that clearly
showed that persistent, near-monochromatic baroclinic
wave flows could be readily sustained in a system without
a substantial inner cylinder. It is likely, therefore, that early
efforts failed to observe such a regular regime in the ther-
mally driven, open cylinder geometry because of a lack of
Figure 1.2.
Selection of images adapted from
Vettin
[1884]
(see http://www.schweizerbart.de). Reproduced with permis-
sion from the publishers, showing the layout of his rotating
convection experiment and some results.
regime, since the flows Vettin observed showed little evi-
dence for the instabilities we now know as “baroclinic
instability” or “sloping convection” [
Hide and Mason
,
1975].
As an historical aside, it is interesting to note that early
meteorologists such as
Abbe
[1907] intended for labora-
tory experiments of this type to serve also as models
of the first kind, i.e., as application-oriented, predictive
model atmospheres. They realized that, while it might
be possible in principle to use the equations of atmo-
spheric dynamics to determine future weather, they were
beyond the capacity of mathematical analysis to solve.
They hoped to use these so-called mechanical integra-
tors [
Rossby
, 1926] under complicated external forcing
corresponding to the observations of the day to repro-
duce and predict very specific low phenomena observed in
the atmosphere. It was anticipated that many such exper-
iments would be built representing different regions of
Earth's surface or different times of year, such as when
the cross-equatorial airflow is perturbed by the monsoon
[
Abbe
, 1907] (although it is not clear whether such an
