High-Latitude Electrodynamics - The Earth's Ionosphere: Plasma Physics and Electrodynamics - page 399

DE-B Convection parameters
Day 5 82148 Orbit 5 4451 Southern Hemisphere

2500
2000
1500
1000
500

0

500
21000
21500
22000
2

2

2500

8:55
622
18.82
67.99

UT (hr:min)
ALT (km)
MLT (hrs)
ILAT (deg)

8:43
455
4.92
66.71

8:46
499
3.51
76.99

8:49
542
21.89
85.55

8:52
584
19.44
78.98

Day 5 82138 Orbit 5 4301 Northern Hemisphere

2500
2000
1500
1000
500
0

2500
2 1000

2 1500

22000
22500

UT (hr: min)
ALT (km)
MLT (hrs)
ILAT (deg)

10:41
732
18.44
64.88

10:44
712
18.29
74.64

10:47
685
17.84
83.70

10:50
650
10.42

10:53
609
7.29
75.54

10:56
569
6.98
65.65

(b)

Figure 8.8b The antisunward component of the plasma velocity, measured in both the
Northern and Southern Hemispheres, is plotted as a satellite moves across the auroral
zone and polar cap.

cell is crescent-shaped. The latter surrounds a portion of the circular cell. The
placement of the small and large cells depends to first order on the sign of B y .
When the IMF has a southward component, the signature of a two-cell con-
vection pattern is seen well beyond the dawn-dusk meridian into the nightside.
The nightside convection pattern, however, does have some distinctive geometric
characteristics that are related to the field-aligned and horizontal currents, which
are described later. Figure 8.10 illustrates the variety of convection geometries
that are seen.

8.2.2 Observations During Northward IMF
A significant departure from the previously described convection patterns is seen
when the IMF has a northward component. In this case the convection velocity is
usually much more structured and of smaller magnitude. When the identification