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6.7.2 Multiexperimental Observations of Midlatitude Structures
Surprisingly, neutral atmosphere perturbations, some of them periodic, have also
been seen in conjunction with VHF radar echoes (Kane et al., 2001). Figure 6.35
shows a spectacular set of sodium atom pillars over Arecibo. Panel b shows
that these were accompanied by strong VHF echoes related to the plasma layers,
which are added to the plot in panel c. We are just beginning to understand this
type of coupling between ion and neutral plasma instabilities.
A number of rocket/radar experiments have been dedicated to the study of
midlatitude E-region plasma processes. An early one (Kelley et al., 1995) found
that the plasma layer was organized horizontally by periodic structures with
a scale of 15 km and an amplitude of the order of 50% (
n
). One of these
features had additional fluctuations that extended from a peak at 30m to well
into the m-scale. The rocket only caught the end of the event in time and space,
but the VHF radar data clearly showed Q-P-type organization. The spectrum
of density fluctuations was almost identical to that of the localized electric field
structures presented in Section 6.7.7.
δ
n
/
16 February 1998
105
105
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10
Max
0
2
95
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10
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90
220
Min
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85
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20
21
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23
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02
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Local time (AST)
Local time (AST)
(a)
(b)
105
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2.0 3 10
4
95
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4
1.0
3
90
0
85
80
20
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Local time (AST)
(c)
Figure 6.35
Sodium atom density contours (a), with VHF backscatter overlay (b), and
with ISR sporadic E density overlay (c) for the nights of February 16-17, 1998. Unfortu-
nately, the radar data are noisy due to interference. [After Kane et al. (2001). Reproduced
with permission of the American Geophysical Union.] See Color Plate 22.
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