Geoscience Reference
In-Depth Information
30
20
Shears
10
0
10
2
10
0
Entire flight
2
10
2
20
Rocket 29.023
Greenland 1985
2
30
E
Power spectra
2
40
10
2
1
10
0
10
1
10
2
10
3
k
(km
2
1
)
Figure 10.16
Wave number spectra of the electric field from a rocket flight in the dayside
auroral oval. The lower plot represents a large spatial region, while the upper plot shows
smaller-scale spectra near auroral arcs. The latter are imbedded in the region sampled to
produce the lower plot. Note that the scales are shifted. [After Earle and Kelley (1993).
Reproduced with permission of the American Geophysical Union.]
clear that any ionospheric plasma gradient
must
be mixed by those applied tur-
bulent electric fields.
The ionosphere is not passive in this context, however. Detailed study has
shown that the magnetosphere behaves as a current generator at these scales
(Vickrey et al., 1986). This in turn implies that the turbulent electric field and
flow velocity are inversely proportional to the ionospheric conductivity. This is
evident when one compares winter and summer hemispheres (e.g., see Fig. 8.8b).
The winter ionosphere has a much more structured velocity field than does
the summer ionosphere. One hypothesis is that the solar wind-driven flow in the
magnetosphere has its own turbulent characteristics that are moderated by the
gross E-region conductivity due to solar lighting conditions, diffuse auroral pre-
cipitation, and polar rain. Superposed on this are localized regions of turbulence
associated with auroral arcs that create plasma and strongly mix it at the same
time. At this scale the E region itself becomes dominated by the precipitation
and the conductivity, and the flow field and plasma content are intertwined in
a fundamental way. A review (Kintner and Seyler, 1985) discussing the interre-
lationship between plasma fluid turbulence and plasma density variations in the
ionosphere has been published. Although no direct conclusions were reached, a
framework was provided for this study and progress is still needed in this area.
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