Geoscience Reference
In-Depth Information
1
General Circulation of Planetary Atmospheres:
Insights from Rotating Annulus and Related Experiments
Peter L. Read 1 , Edgar P. Pérez 2 , Irene M. Moroz 2 , and Roland M. B. Young 1
1.1. LABORATORY EXPERIMENTS
AS “MODELS”OF PHYSICAL SYSTEMS
model, the “conceptual” or “theoretical” model, which
may represent only a small subset of the geographical
detail and physical processes active in the much larger,
applications-oriented model but whose behavior may be
much more completely understood from first principles.
To arrive at such a complete level of understanding, how-
ever, it is usually necessary to make such models as simple
as possible (“but no simpler”) and in geometric domains
that may be much less complicated than found in typi-
cal geophysical contexts. An important prototype of such
a model in fluid mechanics is that of dimensional (or
“scale”) analysis, in which the entire problem reduces to
one of determining the leading order balance of terms
in the governing equations and the consequent depen-
dence of one or more observable parameters in the form
of power law exponents. Following such a scale analysis,
it is often possible to arrive at a scheme of mathematical
approximations that may even permit analytical solutions
to be obtained and analyzed. The well-known quasi-
geostrophic approximation is an important example of
this approach [e.g., see Holton , 1972; Vallis , 2006] that has
enabled a vast number of essential dynamical processes in
large-scale atmospheric and oceanic dynamics to be stud-
ied in simplified (but nonetheless representative) forms.
For the fundamental researcher, such simplified “con-
ceptual”models are an essential device to aid and advance
understanding. The latter is achievable because simplified,
approximated models enable theories and hypotheses to
be formulated in ways that can be tested (i.e., falsified, in
the best traditions of the scientific method) against obser-
vations and/or experiments. The ultimate aim of such
studies in the context of atmospheric and oceanic sciences
is to develop an overarching framework that sets in per-
spective all planetary atmospheres and oceans, of which
Earth represents but one set of examples [ Lorenz , 1967;
Hide , 1970; Hoskins , 1983].
In engineering and the applied sciences, the term
“model” is typically used to denote a device or concept
that imitates the behavior of a physical system as closely
as possible, but on a different (usually smaller) scale,
possibly with some simplifications. The aim of such a
model is normally to evaluate the performance of such
a system for reasons connected with its exploitation for
economic, social, military, or other purposes. In the con-
text of the atmosphere or oceans, numerical weather and
climate prediction models clearly fall into this category.
Such models are extremely complicated entities that seek
to represent the topography, composition, radiative trans-
fer, and dynamics of the atmosphere, oceans, and surface
in great detail. As a result, it is generally impossible to
comprehend fully the complex interactions of physical
processes and scales of motion that occur within any given
simulation. The success of such models can only be judged
by the accuracy of their predictions as directly verified
(in the case of numerical weather prediction) against sub-
sequent observations and measurements. Similar models
used for climate prediction, however, are often compara-
ble in complexity to those used for weather prediction but
are frequently used as tools in attempts to address ques-
tions of economic, social, or political importance (e.g.,
concerning the impact of increasing anthropogenic green-
house gas emissions) for which little or no verifying data
may be available.
In formulating such models and interpreting their
results, it is necessary to make use of a different class of
1 Atmospheric, Oceanic & Planetary Physics, University of
Oxford, Oxford, United Kingdom.
2 Mathematical
Institute, University of Oxford, Oxford,
United Kingdom.
 
 
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