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balance a net current flows into one pole and out the other. This current must
close in the solar wind in the direction perpendicular to the ecliptic (Kelley and
Makela, 2002).
8.5.3 Dependence on Magnetic Activity, IMF, and Season
When the IMF has a southward component, some qualitative descriptions of
the ionospheric field-aligned currents are available in terms of their dependence
on the degree of magnetic activity, on the sign of B y , and on season. In all of
these descriptions, the field-aligned current density is regarded as being uniform
in each of the Region 1 and Region 2 rings, so a magnitude and a local time
distribution can be ascribed to them. A comparison of the upper and lower
panels of Fig. 8.26 shows that the local time distribution is only slightly affected
Current into ionosphere
Current away from ionosphere
2.5
|
| > 100 g
AL
2.0
1.5
1.0
0.5
0
12
14
16
18
20
202468 0 2
2.0
|
| , 100 g
AL
1.5
1.0
0.5
0
12
14
16
18 20 22
Geomagnetic dipole local time
02468 0 2
Figure 8.26 Region 1 and Region 2 currents plotted as a function of local time for quiet
and disturbed geomagnetic conditions. The Region 1 currents have maxima near 14.00
and 8
00 h where they exceed the Region 2 currents. Elsewhere the Region 1 and Region 2
currents are about the same magnitude and show little variation with local time. [After
Iijima and Potemra (1978). Reproduced with permission of the American Geophysical
Union.]
.
 
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