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| Titel |
Field-aligned conductance values estimated from Maxwellian and kappa distributions in quiet and disturbed events using Freja electron data |
| VerfasserIn |
A. Olsson, P. Janhunen  |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 16, no. 3 ; Nr. 16, no. 3, S.298-302 |
| Datensatznummer |
250013197
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| Publikation (Nr.) |
 copernicus.org/angeo-16-298-1998.pdf |
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| Zusammenfassung |
We study the question of what difference it
makes for the derived field-aligned conductance (K) values if one uses
Maxwellian or kappa distributions for the fitting of low-orbiting satellite
electron flux spectra in the auroral region. This question has arisen because
sometimes a high-energy tail is seen in the spectra. In principle, the kappa
fits should always be better, because the kappa distribution is a generalization
of the Maxwellian. However, the physical meaning of the parameters appearing in
the Maxwellian is clearer. It therefore makes sense to study under which
circumstances it is appropriate to use a Maxwellian. We use Freja electron data
(TESP and MATE) from two events. One of the events represents quiet
magnetospheric conditions (stable arc) and the other represents disturbed
conditions (surge). In these Freja events, at least, using kappa rather than
Maxwellian fitting gives a better fit to the observed distribution, but the
difference in K values is not large (usually less than 20). The
difference can be of either sign. However, sometimes even the kappa distribution
does not provide a good fit, and one needs a more complicated distribution such
as two Maxwellians. We investigate the relative contributions of the two
Maxwellians to the total field-aligned conductance value in these cases. We find
that the contribution of the high-energy population is insignificant (usually
much less than 20). This is because K is proportional to n∕ Ec, where n is the source plasma density and Ec is the
characteristic energy.
Key words. Field-aligned conductance · Maxwellian
distribution · Kappa distribution · Freja electron data |
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