Geoscience Reference
In-Depth Information
2:10 LT
2:18 LT
2:26 LT
46
45
44
43
42
41
40
39
2:34 LT
2:42 LT
2:50 LT
46
45
44
43
42
41
40
39
2:58 LT
3:06 LT
3:13 LT
46
45
44
43
42
41
40
39
278
280
282
284
286
288
278
280
282
284
286
288
278
280
282
284
286
288
Longitude (8E)
Longitude (8E)
Longitude (8E)
Figure 10.6a Series of SAR arc images observed from Ithaca, NY, on October 28-29,
2000. The arc is centered at 40 geographical latitude, while the edge of the diffuse aurora
is near 43 N. [After Nicolls et al. (2005). Reprinted with permission of the Institute of
Electrical and Electronics Engineers, Inc. (© 2005, IEEE).] See Color Plate 28.
For F-region physics we are most concerned with “soft” particles—that is, elec-
trons with energy less than about 500 eV—since they deposit their energy at the
highest altitudes. Vertical transport by diffusion is crucial, however, since even
soft electrons produce plasma at relatively low altitudes. Electron heat conduc-
tion is also very important because secondary electrons are much more energetic
than the ionospheric electrons and may heat the latter quickly, depending on the
ratio of two electron populations. This can create a redistribution of plasma at
high altitudes which mirrors the horizontal precipitation pattern.
As discussed briefly in Chapter 1, soft electrons most copiously precipitate in
the dayside cusp region, where magnetosheath plasma is in direct contact with the
ionosphere. This occurs in the dayside auroral oval at invariant latitudes in the
range 70-74 . Our interest here is not so much in the ionization process, which
is more the topic of classical aeronomy (see, for example, Banks and Kockarts,
1973), as in the resulting horizontal variation in plasma content and structure.
Strong evidence that the equatorward boundary of structured plasma in the
 
Search WWH ::




Custom Search