Geography Reference
In-Depth Information
CHAPTER 12
Middle Atmosphere Dynamics
The
middle atmosphere
is generally regarded as the region extending from the
tropopause (about 10-16 km altitude depending on latitude) to about 100 km. The
bulk of the middle atmosphere consists of two main layers, the
stratosphere
and
the
mesosphere
, which are distinguished on the basis of temperature stratification
(Fig. 12.1). The stratosphere, which has large static stability associated with an
overall increase of temperature with height, extends from the tropopause to the
stratopause
at about 50 km. The mesosphere, which has a lapse rate similar to
that in the troposphere, extends from the stratopause to the
mesopause
at about
80-90 km.
Previous chapters of this text have focused almost exclusively on the dynamics
of the troposphere. The troposphere accounts for about 85% of the total mass
of the atmosphere and virtually all atmospheric water. There can be little doubt
that processes occurring in the troposphere are primarily responsible for weather
disturbances and climate variability. Nevertheless the middle atmosphere cannot be
neglected. The troposphere and the middle atmosphere are linked through radiative
and dynamical processes that must be represented in global forecast and climate
models. They are also linked through the exchange of trace substances that are
important in the photochemistry of the ozone layer. This chapter focuses primarily
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