Dynamics and Electrodynamics of the Equatorial Zone - The Earth's Ionosphere: Plasma Physics and Electrodynamics - page 82

zonal drift and maximum vertical electric field (downward) are about 150m/s
and 4.5mV/m, respectively. This observed nighttime plasma velocity is consis-
tent in magnitude and direction with the eastward zonal neutral thermospheric
wind found experimentally and discussed previously. The vertical pattern of the
nighttime electric field is thus consistent with the simple F-region dynamo model
we have presented.
To understand the diurnal variation in more detail, however, we need to con-
sider the role of the “end” plates in the E layer, which, contrary to the approxima-
tion used previously, are good conductors during the day. First, consider again
an idealized slab geometry that ignores the magnetic field line curvature and dip
angle but includes conductivity variations with distance ( y

along the magnetic
field direction. The actual geometry is shown schematically in Fig. 3.9a, and the
slab model is shown in Fig. 3.9b. There are no variations in the x direction.
In this model the wind is a function of z in the F layer but goes to zero in the
E layer. The finite density in the E layer and its attendant conductivity act as an
electric load on the dynamo. (In this three-level slab model we take the E-layer

)

E

F region

Slab

y 50

E region

E

y 5 y 1

y 52 y 1

E

N S

y 5 y 2

y 52 y 2

y 5 y 3 y 52 y 3

Equator

Actual Geometry
(a)

y 5 y 3

y 5 y 2 E J

Northern E region

y 5 y 1

F layer valley ( P small)

y 50

E J

y 52 y 1

F layer dynamo region

B

y 52 y 2

y 52 y 3

E J

Southern E region

Slab geometry

(b)

Figure 3.9 (a) Side view of the dipole magnetic field geometry near the magnetic equator.
The curves are exaggerated to show the coupling geometry between the F region at the
equator and the off-equatorial E region. (b) F-layer slab geometry including conducting
end plates in the northern and southern hemispheres.