Geography Reference
In-Depth Information
CHAPTER 1
Introduction
1.1
THE ATMOSPHERIC CONTINUUM
Dynamic meteorology is the study of those motions of the atmosphere that are
associated with weather and climate. For all such motions the discrete molecular
nature of the atmosphere can be ignored, and the atmosphere can be regarded as
a continuous fluid medium, or
continuum
. A “point” in the continuum is regarded
as a volume element that is very small compared with the volume of atmosphere
under consideration, but still contains a large number of molecules. The expres-
sions
air parcel
and
air particle
are both commonly used to refer to such a point.
The various physical quantities that characterize the state of the atmosphere (e.g.,
pressure, density, temperature) are assumed to have unique values at each point in
the atmospheric continuum. Moreover, these
field variables
and their derivatives
are assumed to be continuous functions of space and time. The fundamental laws
of fluid mechanics and thermodynamics, which govern the motions of the atmo-
sphere, may then be expressed in terms of partial differential equations involv-
ing the field variables as dependent variables and space and time as independent
variables.
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