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N
e
(cm
23
)
10
5
0
33.02
7
~C
s
110
J
(model)
V
100
V
d
N
e (meas)
90
0
250
500
18.15
0
110
J
(meas)
V
100
V
d
N
e (meas)
90
Re-entry noise
0
250
500
14.53
2
J
(model)
110
V
100
V
d
N
e (meas)
90
0
5
10
0
250 500
Velocity (m/s)
0 0.5 1.0
Wave number (m
21
)
(c)
0
250
500
J(A/km
2
)
(a)
Frequency (Hz)
(d)
(b)
Figure 4.33
(a) Measured or model current and smoothed electron density profiles for
each of three experiments; (b) calculated electron drift and phase velocity profiles com-
puted using the values in (a); (c) gray-scale representation of the growth rate calculated
from the linear dispersion relation for horizontal waves using the model parameters dis-
cussed in the text. Darker shades represent higher values of
γ
, whereas white indicates that
γ<
0. (d) Frequency-height sonograms showing rocket-measured irregularities. [After
Pfaff et al. (1985). Reproduced with permission of Pergamon Press.]
electron drift velocity, the phase velocity for two-stream waves (which must
exceed
C
s
for instability to occur), and the approximate value for
C
s
. Using
these parameters and the gradient of the electron density profile, the growth rate
has been calculated as a function of altitude and wave number in panel (c) using
a gray scale. Two-stream waves result when the threshold for the two-stream
instability is exceeded. This condition occurred only in the CONDOR rocket
flight shown on top and is evident in the linear calculation [panel (c)] as well
as the wave observations in panel (d). In the calculation, waves are predicted to
grow at high wave numbers. Indeed, sonograms of the rocket wave fluctuation
data in panel (d) show strong high-frequency (in the rocket frame) waves in
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