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| Titel |
Non-conjugate aurora and inter hemispheric currents |
| VerfasserIn |
J. P. Reistad, N. Østgaard, K. M. Laundal, K. Oksavik |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250060639
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| Zusammenfassung |
| We look at large scale auroral features using global imagers to obtain simultaneous pictures
of both the southern and northern auroral ovals in the ultra violet part of the spectra. During
the years 2001 and 2002 the IMAGE satellite was in a favourable position for imaging the
aurora borealis (Northern Hemisphere) and the POLAR satellite with its large field-of-view
VIS Earth camera had a sporadic coverage of the aurora australis (Southern Hemisphere). In
total 19 hours of simultaneous global imaging from different seasons are analysed searching
for non-conjugacy in the night side sector. By non-conjugate aurora we mean auroral features
appearing in one hemisphere only, or significant differences in intensity between the
hemispheres for the same auroral feature. We suggest that our observed large scale
asymmetries can be explained in terms of inter hemispheric currents (IHC). Coherent
with our earlier findings, we list three possible candidates for producing such inter
hemispheric currents based on observations. 1) Hemispherical differences in the
solar wind dynamo due to IMF Bx and tilt angle producing different strength of
region 1 currents in the conjugate he mispheres, 2) Hemispherical differences in
conductivity controlled by the tilt angle only giving rise to IHC on closed field lines,
and 3) Field-aligned current components induced by the penetration of the IMF
By into the closed magnetosphere. Most of the observed non-conjugate aurora in
our dataset can be explained by these candidates only. The IMF By penetration
candidate is considered closer. We search for evidence in our data that IMF By < 0
(By > 0) can induce an IHC producing stronger aurora on the polar boundary in the
Northern (Southern) Hemisphere. Also a second IHC component are predicted from the
theory, mapping to the equatorward part of the oval and opposite directed along
the magnetic field lines. Using a much larger dataset for one hemisphere only, we
show whether these predicted currents can be identified from global images. As far
as we know, these currents have only been predicted but never observed earlier. |
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