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| Titel |
Investigations of the auroral luminosity distribution and the dynamics of discrete auroral forms in a historical retrospective |
| VerfasserIn |
Y. I. Feldstein, V. G. Vorobjev, V. L. Zverev, M. Forster |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
2190-5010
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| Digitales Dokument |
URL |
| Erschienen |
In: History of Geo- and Space Sciences ; 5, no. 1 ; Nr. 5, no. 1 (2014-05-21), S.81-134 |
| Datensatznummer |
250115309
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| Publikation (Nr.) |
 copernicus.org/hgss-5-81-2014.pdf |
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| Zusammenfassung |
| Research results about planetary-scale
auroral distributions are presented in a historical retrospective, beginning
with the first "maps of isochasms" – lines of equal visibility of auroras
in the firmament (Fig. 2) – up to "isoaurora maps" – lines of
equal occurrence frequency of auroras in the zenith (Fig. 4). The
exploration of auroras in Russia from Lomonosov in the 18th century
(Fig. 1) until the start of the International Geophysical Year (IGY)
in 1957 is shortly summed up. A generalised pattern of discrete auroral forms
along the auroral oval during geomagnetically very quiet intervals is
presented in Fig. 5. The changes of discrete auroral forms versus
local time exhibit a fixed pattern with respect to the sun. The auroral forms
comprise rays near noon, homogeneous arcs during the evening, and rayed arcs
and bands during the night and in the morning. This fixed auroral pattern is
unsettled during disturbances, which occur sometimes even during very quiet
intervals. The azimuths of extended auroral forms vary with local time. Such
variations in the orientation of extended forms above stations in the auroral
zone have been used by various investigators to determine the position of the
auroral oval (Fig. 9). Auroral luminosity of the daytime and
nighttime sectors differ owing to different luminosity forms, directions of
motion of the discrete forms, the height of the luminescent layers, and the
spectral composition (predominant red emissions during daytime and green
emissions during the night). Schemes that summarise principal peculiarities
of daytime luminosity, its structure in MLT (magnetic local
time) and MLat (magnetic latitude) coordinates, and the
spectral composition of the luminosity are presented in Figs. 15 and
19. We discuss in detail the daytime sector dynamics of individual
discrete forms for both quiet conditions and auroral substorms. The most
important auroral changes during substorms occur in the nighttime sector. We
present the evolution of conceptions about the succession of discrete auroral
forms and their dynamics during disturbance intervals. This ranges from
Birkeland's polar elementary storms, over the prospect of a fixed auroral
pattern up to the auroral substorm model. The classic schemes of the spatial
distribution and motion of discrete auroral forms during single substorms are
shown in Fig. 20 (expansive and recovery phases) and
Fig. 21 (creation, expansive and recovery phases). In this review we
discuss various models of bulge formation, in particular as a result of new
formation of arcs about 50–100 km poleward of previously existing auroral
structures (Fig. 24). Discrete steps in the development of an
expanding bulge are separated by 1–3 min from each other. The model of
successive activations confines only to a ~40° longitudinal
portion of the magnetotail (Fig. 28). We consider differences in the
development of single substorms and substorms during magnetic storms. The
structure and dynamics of auroras during steady magnetospheric convection
(SMC) periods are dealt with in Sect. 8. A generalised scheme
of the auroral distribution during SMC periods is shown in Fig. 34.
Separate sections describe discrete auroras in the polar cap
(Sect. 5), and the diffuse luminosity equatorward of the auroral
oval (Sect. 9). Visual observations of diffuse auroral forms
at midlatitudes suggest that the whole latitudinal interval between the
auroral oval and the stable auroral red (SAR) arc is filled up with diffuse
luminosity. SAR arcs with intensities of several tens of Rayleigh enclose
systematically the region of diffuse luminosity; they are positioned at the
border of the plasmasphere. |
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