Dynamics and Electrodynamics of the Equatorial Zone - The Earth's Ionosphere: Plasma Physics and Electrodynamics - page 102

Day Night

Wind

U

E E

F region

E Z ~ 2 ( U 3 B ) Z

West East

B

J E

E

E
J

E region

J ~0

Figure 3.20 Simplified model of the F-region prereversal enhancement driven by a uni-
form F-region wind, U . Near the sunset terminator the F-region dynamo E z is no longer
shorted out and approaches B . This field maps to an equatorward E θ in the E layer

and drives a westward Hall current, J θφ . But if no current flows in the nightside E region,
a negative polarization charge must develop at the terminator, with E φ as shown and J φφ
canceling J θφ . This E φ maps back to the F region and causes first an upward (day) and
then a downward (night) E

− U ×

×

B plasma drift. [After Farley et al. (1986). Reproduced with
permission of the American Geophysical Union.]

below the F peak (R. Heelis, personal communication, 2002). On the other hand,
Eccles (1998a, b) pointed out that simply setting 0 will generate a zonal

electric field pulse due to the spatial variation of the vertical component. A third
mechanism by Haerendel and Eccles (1992) suggests that the electrojet partially
closes after sunset through a poorly conducting F-region valley, creating electric
fields. After studying a counterelectrojet event that produced a reversed sign of
the PRE, Kelley et al. (2009a) concluded that the Haerendel/Eccles mechanism
must dominate.
As we shall see, this vertical drift enhancement has many interesting conse-
quences. It can produce conditions that are favorable to plasma instabilities,
and an extremely structured ionosphere often results (see Chapter 4). Significant
effects on neutral atmospheric dynamics also occur.

∇ × E =

3.4.2 High-Latitude Effects on the Equatorial Electric Field
The equatorial plasma is not always as well behaved as indicated thus far.
A number of interesting processes can affect equatorial electrodynamics, in addi-
tion to the neutral wind-generated electric fields already discussed, which are
driven by the solar heat input carried by photons. Energy also comes from the
sun via particles in the solar wind and via the electromagnetic (Poynting) flux
in the solar wind. These energy sources affect primarily the high-latitude polar