Geography Reference
In-Depth Information
CHAPTER 9
Mesoscale Circulations
The previous chapters focused primarily on the dynamics of synoptic and plan-
etary scale circulations. Such large-scale motions are strongly influenced by the
rotation of the earth so that outside the equatorial zone the Coriolis force dominates
over inertia (i.e., the Rossby number is small). To a first approximation, as shown
in Chapter 6, large-scale motions can be modeled by quasi-geostrophic theory.
The study of quasi-geostrophic motions has been a central theme of dynamic
meteorology for many years. Not all important circulations fit into the quasi-
geostrophic classification, however. Some have Rossby numbers of order unity,
and some are hardly at all influenced by the rotation of the earth. Such circulations
include a wide variety of phenomena. They all, however, are characterized by
horizontal scales that are smaller than the synoptic scale (i.e., the
macroscale
of
motion), but larger than the scale of an individual fair weather cumulus cloud
(i.e., the
microscale
). Hence, they can be classified conveniently as
mesoscale
circulations. Most severe weather is associated with mesoscale motion systems.
Thus, understanding of the mesoscale is of both scientific and practical importance.
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