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SOUSY radar reflectivity (m
2
/m
3
)
90
89
MAC/SINE 15.245
07/14/87
0929 UT
88
87
86
85
84
83
82
81
80
10
2
10
3
10
4
Electron density (cm
23
)
Figure 7.10
Comparison of rocket measurements of the electron density profile (solid
line) with the simultaneous 53.5MHz SOUSY radar observations of radar reflectivity (o)
during the MAC/SINE campaign. [After Alcala et al. (2001). Reproduced with permission
of the American Geophysical Union.]
and others that did not, but the VHF echoes fill the whole height range. Both
turbulent and edge scatter thus seem to occur, with the former dominating.
The complementary roles of active turbulence and sharp edges in PMSE are
upheld by Figs. 7.10 and 7.11. Figure 7.12 indicates that a third mechanism
plays a role. These data are the first simultaneous measurements of radar echoes,
electron density, and neutral density fluctuations (Lübken et al., 1993). The
three phenomena clearly are not collocated, suggesting that turbulence in the
passive scalar electrons may outlive the active neutral turbulence that created it.
This fossil turbulence idea has been quantitatively verified by Rapp and Lübken
(2004a, b).
Both passive scalar mixing and edge scatter can be related to one dimensionless
parameter: the Schmidt number (
S
c
)
, defined by
S
c
=
ν/
D
A
(7.7)
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