High-Latitude Electrodynamics - The Earth's Ionosphere: Plasma Physics and Electrodynamics - page 390

S

W

B y

(b)

(a)

B y

d/2 d/2

E x

J z

B y

J z

p ± 0

Dawn Dusk

h

J x 5 p E x

Figure 8.4 Schematic representation of field-aligned currents and closure currents in the
polar cap ionosphere and the electric and magnetic fields associated with them.

or

p = δ B y /μ 0 δ E x (8.17d)

p the electric and magnetic fields
at altitudes away from the ionospheric load should be highly correlated. DE-2
satellite observations have shown some events with just such correlations at a
99% confidence level (Sugiura et al., 1982), although Smiddy et al. (1980) have
also shown examples where the correlation breaks down. The latter authors have
interpreted their results in terms of the E I · ∇ ⊥ p , term in (8.14) and (8.15), which
must be ignored to derive the relationship above.
One may consider the solar wind MHD generator as a voltage source
characterized by the electric field

These expressions show that for a uniform

δ E , which is attached to a resistive load

characterized by p . Then (8.17a) yields the perturbation magnetic field as a

function of the load conductivity. This viewpoint may be applicable for the large-
scale magnetosphere-ionosphere interaction (Lysak, 1985). Alternatively, the
generator may be viewed as a current source. There is some evidence that
the latter viewpoint is more accurate at smaller scales

( ≤ 100 km ) , since the