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4
Equatorial Plasma Instabilities
and Mesospheric Turbulence
In this chapter we study the plasma physics and aspects of neutral turbulence at low
latitudes in the earth's ionosphere. Most of the information we have concerning
these processes comes from radio wave scattering or reflection experiments con-
ducted from the surface of the earth. In situ measurements made with rocket- and
satellite-borne sensors have also contributed significantly to our present under-
standing. As in the previous chapter, instabilities occurring in the F region are
addressed first, followed by consideration of lower-altitude phenomena. We also
discuss mesospheric turbulence because plasma turbulence is often described in an
analogous manner.
4.1 F-Region Plasma Instabilities: Observations
Plasma instability phenomena occurring in the equatorial F-region ionosphere
are usually grouped under the generic name equatorial spread F (ESF). This stems
from the earliest observations using ionosondes, which showed that on occasion
the reflected echo did not display a well-behaved pattern but was “spread” in
range or frequency (Berkner andWells, 1934). A physics-based name for this phe-
nomenon is “convective equatorial ionospheric storm” (CEIS). The phenomenon
occurs primarily at night, although isolated daytime events occur (Woodman
et al., 1985; Chau and Woodman, 2001). The modern era in CEIS (ESF) studies
began on a “low” theoretical note in 1970 with the publication of the first com-
pilation of measurements made by the Jicamarca Radar Observatory in Peru
(Farley et al., 1970). The authors concluded that no theory published to date
could explain the data! Fortunately, considerable progress has occurred since
then, and the theory has kept pace with continuing additions and improvements
in the data.
In the early 1970s, range-time-intensity (RTI) “weather” radar maps came
into vogue as a method of following the position and intensity of CEIS plasma
density irregularities. Since the Jicamarca radar is stationary and has a small field
of view (
1
◦
), the RTI maps are similar to pictures from a slit camera. One of the
more spectacular examples of the maps obtained at the Jicamarca Observatory is
∼
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