Dynamics and Electrodynamics of the Equatorial Zone - The Earth's Ionosphere: Plasma Physics and Electrodynamics - page 107

Sun

Sun

Shielding
charges

Plasmapause

1 1 2
2

1 1 2
2

1 1

Dawn-dusk
electric field

Magnetopause

Steady state
strong convection
with shielded plasmasphere

Transient state
when magnetospheric
electric field decreases

Figure 3.24a A schematic diagram drawn in the equatorial plane showing how a rapid
decrease in magnetospheric convection could create electric field changes inside the
plasmasphere.

So lar win d

J

J

J

E

Plasmasheet Plasmasheet

E E

II I I II

Dusk auroral oval

Dawn auroral oval

Polar cap

J J

E E

Daytime ionosphere
Region I . Region II

J

E

Daytime ionosphere
Region II

. Region I

J

E

Figure 3.24b Circuit diagram looking from the sun. Polarities of closure currents are
shown for two different cases of field-aligned current imbalance.

display similar oscillations, as illustrated in Fig. 3.25a. These time variations are
too quick for the charges in the Alfvén layer to change and thus seem to be
consistent with the concept of very effective direct electric field penetration into
the plasmasphere. Power spectra of the electric field (from Alaska and Peru)