Ionospheric Response to Electric Fields - The Earth's Ionosphere: Plasma Physics and Electrodynamics - page 463

9.5 Summary
In this chapter we have discussed a variety of phenomena observed in the high-
latitude ionosphere. Knowledge of the current and prior convective history of the
plasma and the magnetic field topology encountered by that plasma is essential
to understanding or explaining many phenomena.
When considering plasma near the F peak, the local solar zenith angle, the
time at which the flux tube encountered the auroral ionization source, the spa-
tial variation of the drift velocity along the convection path, and the length
of time the drift allows the plasma to reside in a production region must all
be taken into account. The magnetic field topology is a minor consideration.
The midlatitude trough, for example, can be understood in this manner. Above
the F peak, the magnetic field topology is an important consideration, as is the
plasma temperature. They will both affect the field-aligned motion of the plasma
and its topside distribution. The light ion trough can be understood with these
considerations. Progress toward a more complete understanding of the high-
latitude ionospheric plasma will undoubtedly require multipoint measurements
that provide some information about the time history of the plasma motion and
the ionization sources it encounters. Some data sets of this nature are available
from simultaneous measurements made by rockets, satellites, and ground-based
instrumentation, but they must be integrated into a study that includes a versatile
computer model in order to sort out the most important processes.
At the top of the ionosphere, dramatic particle acceleration zones exist. At 500-
1000 km, ions are transversely accelerated far beyond escape speed, supplying
the magnetosphere with hot oxygen ions. Above this height, near 5000 km, both
ions and electrons are accelerated by parallel electric fields, forming the classic
electron-induced aurora and precipitating oxygen ions and protons. The upward
parallel fields also expel hot ions into the magnetosphere and create “black”
aurora.
The effect of plasma dynamics on the neutral atmosphere can also be quite
dramatic. Numerous measurements have shown extremely strong winds in the
high-latitude thermosphere. Simultaneous plasma velocity measurements show
clearly that these winds are driven by electric fields that are impressed from above
through interactions between the earth's magnetosphere and the solar wind.
This control of the earth's upper atmosphere by interplanetary processes is a
fascinating example of the interaction between a flowing plasma and a planetary
atmosphere.
References
Banks, P. M., and Holzer, T. E. (1969). Features of plasma transport in the upper
atmosphere. J. Geophys. Res. 74 , 6304.
Brinton, H. C., Grebowsky, J. M., and Brace, L. H. (1978). The high-latitude winter
F region at 300 km: Thermal plasma observations from AE-C. J. Geophys. Res .
83 , 4769.