Geoscience Reference
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June 15-16, 1980
Arecibo, P.R.
450
375
300
40
0
June 15-16, 1980
Arecibo, P.R.
80
40
Neutral velocity
0
0
80
10
Ion velocity
0
5
0
20
00
04
08
20
00
04
08
Time (LT)
Time (LT)
(a)
(b)
Figure 5.18
(a) Height of the peak electron density (
h
max
)
, meridional plasma drift
velocity components (
V
⊥
N
and
V
||
), and peak in electron density (
n
max
)
measured over
Arecibo for June 15-16, 1980. (b) Horizontal neutral winds and ion drift velocities (pos-
itive northward) for the same night as the data shown in (a). [After Behnke et al. (1985).
Reproduced with permission of the American Geophysical Union.]
ion motion,
V
, was directed
oppositely
to the parallel component of the local
neutral wind until 0100. Although counterintuitive, this situation can occur if
a strong downward gravity-driven velocity is simultaneously present due to the
high altitude of the layer. In fact, Burnside et al. (1983) have calculated the
gravity term for this data set and have found that indeed the downward flow is
sufficient to overpower the oppositely directed neutral wind during this time. In
this same period (from 2130 LT until 0100), the perpendicular ion flow shown
in Fig. 5.18a was upward, which corresponds to an eastward electric field. But
the neutral wind was equatorward at this time, which would tend to generate a
westward electric field component by the dynamo process. This rules out a local
F-region dynamo process as a source of the electric field. Magnetic activity was
low, so there is no reason to expect a magnetospheric origin for the eastward
zonal electric field. A more likely explanation is an electric field that mapped
from the other hemisphere. In fact, if the neutral wind extended into the Southern
Hemisphere with the same direction (toward the south pole) and generated an F-
layer dynamo field at the conjugate point, the zonal component in the Northern
Hemisphere would be eastward as observed. This postulated south-poleward
wind in the Southern Hemisphere would also tend to keep the F layer low,
which in turn would enhance the Southern Hemisphere Pedersen conductivity.
If two ends of a magnetic field line with differing dynamo wind fields compete for
||
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