Geoscience Reference
In-Depth Information
Fig. 2.3
A typical profile of neutral atmospheric temperature. Taken from the site
http://www.
Various physical mechanisms for the atmospheric gas motion result in permanent
motions of the upper atmosphere (e.g., see Hines
1974
). The basic long-period
motions of the lower thermospheric dynamics are the average daily circulation,
including both the zonal and meridional circulation, the diurnal and semidiurnal
atmospheric tides, the internal gravity and acoustic waves and the turbulence. The
oscillation period of the semidiurnal and diurnal tides are 12 and 24 h, respectively,
while the motions with period approximately several hours are usually referred
to as internal gravity waves (IGWs). Notice that due to a variety of turbulent
mixing phenomena the atmosphere is relatively uniform in composition below about
100 km.
The diurnal tides are due to both the solar heating of the sunlit atmosphere, which
results in rarefaction of the atmosphere, and the cooling of the nightside atmosphere
is followed by its compression. The diurnal variations of the atmosphere heating and
cooling excite the tide waves, which in turn produce the atmospheric gas motion
in the horizontal direction. The tides generated at tropospheric and stratospheric
heights can excite the lower E-region winds. The amplitude of the diurnal vari-
ations of the wind velocity increases from 10-30 m/s at the altitude 95 km up to
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