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upper electrojet, the wave frequency in the drift frame becomes small and the
electrons may again be isothermal (Hysell et al., 2007).
St.-Maurice et al. (2003) reported observations of two-step type-I waves
in the lower equatorial electrojet moving at speeds higher even than in adia-
batic processes and up to 50% higher than the isothermal ion acoustic speed.
They named such behavior super-adiabatic and found that only the theory by
St.-Maurice and Kissack (2000), which included electron thermal corrections,
could explain these waves. The next step, exploring aspect sensitivity (Kagan and
St.-Maurice, 2004), showed good correspondence to observations (Kudeki and
Farley, 1989) and good qualitative agreement with the observed altitude behavior
of Farley-Buneman waves: super-adiabatic at lower altitudes and isothermal at
high altitudes. The correspondence of linear phase velocities at marginal stability
to observations stimulated further linear theory with nonisothermal electrons,
as reported by Kissack et al. (2007a, b). These papers additionally account for
nonzero flow angles (essentially the angle between the
E
B
direction and the
center of the radar beam, important for nonzero zenith angle transmissions) and
an arbitrary heat source (with possible applications for high latitudes and heating
experiments). A step forward by Kissack et al. (2007a, b) was the presentation
of thermal corrections, which showed contributions from each physical process.
They were also able to recover the results of preceding linear theories.
To test the wavelength dependence predicted by the Kissack et al. theory,
Kagan and Kissack (2007) analyzed the multi(3)-frequency experiment of Balsley
and Farley (1971) in Jicamarca. Their theoretical predictions showed good corre-
spondence to observations. They also showed that, depending on the frequency
of two-stream waves, their altitude behavior changes from super-adiabatic at
lower altitudes to isothermal at higher altitudes. The transitional process from
super-adiabatic to isothermal is dominated by inelastic electron energy exchange
and therefore is much more important at low radar frequencies. In Fig. 4.32b
×
Transitional
114
114
114
16 MHz
50 MHz
146 MHz
112
112
112
110
108
110
110
108
108
106
106
106
e
5
0.003
5 0.003
e
5 0.003
e
104
104
104
102
102
102
5
0.007
5 0.007
e
5
0.007
e
e
100
0.01
100
100
0.1
1
10
0.1
1
10
0.1
1
10
100
Figure 4.32b
Altitude dependences of dimensionless parameters
ξ
AT
(dashed lines) and
ξ
T
(solid lines) that define dominating physical processes for inelastic electron cooling rates
δ
e
=
003 (gray lines) for each of three radar frequencies.
Calculations are done with code from Kissack et al. (2007b), revised for the time and
location of Balsley and Farley (1971). [After Kagan and Kissack (2007). Reproduced
with permission of the American Geophysical Union.]
0
.
007 (black lines) and
δ
e
=
0
.
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