Dynamics and Electrodynamics of the Equatorial Zone - The Earth's Ionosphere: Plasma Physics and Electrodynamics - page 85

B

R F
V F

V

V ES

R EN

R ES

V EN

Figure 3.10 Electric circuit analogy to the voltage sources in the equatorial F region.
Off-equatorial E-region wind dynamo competes with the F-region dynamo at the equator
to determine the voltage differences between magnetic field lines.

= ( P ) − 1 . The voltage measured by the meter corresponds to the electric field
times the distance between the two magnetic field lines (the conducting wires).
The battery with the lowest internal resistance determines the voltage and thus
the electric field as well. In the F layer during the nighttime

R

F

P is larger, and the F
region dominates. During the day, E-region sources determine the electric field,
and the F layer acts as a load.
A model calculation of the field line-integrated Pedersen conductivity and the
vertical electric field is presented in Fig. 3.11 as a function of height measured at
the magnetic equator. The local time is 1900, and the driving eastward neutral
wind used in the calculation is taken to be constant with a value of 160m/s. The
model used for the ionospheric plasma density is similar to the data plotted in
Fig. 3.8a except that the E-region density below 150 kmwas taken to be constant
at a value of 2 10 4 cm − 3 . The parenthetical expressions in the figure yield the

percentage of the total

×

P found below 300 km along that particular magnetic
field line. At first glance the P values seem high, since the value of σ P at 300 km

10 − 5 mho/m. However, near the equator the magnetic
field lines are nearly horizontal and are the order of several thousand kilometers
long. Large values of

in Fig. 2.6 is only about 5 ×

P continues to increase with
height above the F peak at about 350 km, even though when measured at the
magnetic equator,

P then result. Notice that

σ P decreases with height above 350 km. This is due to the
length of the field line and to the fact that the field lines crossing the equator
“reenter” the F layer at off-equatorial latitudes where the equatorial anomaly
occurs (see Chapter 5). Above 400 kmaltitude, most of the conductivity is located
in the F layer, and the local thermospheric winds drive the electrical system.
However, as altitude decreases, the E layer begins to short out the electric field