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Polar summer mesosphere
Polar winter mesosphere
Equatorial mesosphere
CONDOR flight 31.028
85.0-85.5 km
STATE 1, July '83
88-89 km
MAP/WINE night M-T5
76.9-77.4 km
0.001
0.01
0.1
1
10
0.001
0.01
0.1
1
10
0.001
0.01
0.1
1
10
0.0
0.0
0.0
21.0
21.0
21.0
2
2.0
2
2.0
2
2.0
2
3.0
2
3.0
23.0
2
4.0
24.0
24.0
25.0
25.0
25.0
26.0
26.0
26.0
2
7.0
2
7.0
2
7.0
2
8.0
28.0
28.0
2
9.0
2
9.0
2
9.0
2
10.0
0.001
2
10.0
0.001
2
10.0
0.001
0.01
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10
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1
10
0.01
0.1
1
10
Wavenumber log scale
Wavenumber log scale
Wavenumber log scale
Figure 7.13
Comparison of mesospheric electron density fluctuation spectra from (left)
polar summer (Ulwick et al., 1988), (middle) polar winter (Blix, 1988), and (right) equa-
torial (Røyrvik and Smith, 1984) rocket launches. The vertical line corresponds to the
Bragg wave number of a 50-MHz radar. [After Cho and Kelley (1993). Reproduced with
permission of the American Geophysical Union.]
not shown) were due to incoherent scatter from this plasma (Nicolls et al.,
2008).
Finally, another idea has arisen (Havnes et al., 1990; Hagfors, 1992; La Hoz,
1992) to explain scatter at even higher frequencies that has been observed in
the polar mesosphere—for example, at 933MHz (Röttger et al., 1990) and at
1290MHz (Cho et al., 1992b). The idea is that an ice particle with charge state
±
Z
will attract a cloud of equal and opposite sign within a few Debye lengths of
the particle. If the radar wavelength is larger than the cloud, the signal scattered
by it is proportional to
Z
2
, thus enhancing the incoherent scatter component of
the return echo (La Hoz et al., 2006).
Radar echoes are thought to be associated with small particles, while the vis-
ible NLC are due to those larger ones
(
r
≈
30 nm
)
capable of forward scat-
tering of visible light
. The simultaneous radar and lidar data in
Fig. 7.14b support this idea. Notice that the lidar (which detects the largest
ice particles) signal is at the lower edge of the radar signal. This seems a clear
indication that the radar detects small particles as they fall and grow larger to
be detected by the lidar just before they begin to sublimate as the temperature
rises.
(λ
≈
500 nm
)
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