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| Titel |
Ionospheric storms at geophysically-equivalent sites – Part 2: Local time storm patterns for sub-auroral ionospheres |
| VerfasserIn |
M. Mendillo, C. Narvaez |
| 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 ; 28, no. 7 ; Nr. 28, no. 7 (2010-07-15), S.1449-1462 |
| Datensatznummer |
250016860
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| Publikation (Nr.) |
 copernicus.org/angeo-28-1449-2010.pdf |
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| Zusammenfassung |
The response of the mid-latitude ionosphere to geomagnetic storms depends
upon several pre-storm conditions, the dominant ones being season and local
time of the storm commencement (SC). The difference between a site's
geographic and geomagnetic latitudes is also of major importance since it
governs the blend of processes linked to solar production and magnetospheric
input, respectively. Case studies of specific storms using ionospheric data
from both hemispheres are inherently dominated by seasonal effects and the
various local times versus longitude of the SCs. To explore
inter-hemispheric consistency of ionospheric storms, we identify
"geophysically-equivalent-sites" as locations where the geographic and
geomagnetic latitudes have the same relationship to each other in both
hemispheres. At the longitudes of the dipole tilt, the differences between
geographic and geomagnetic latitudes are at their extremes, and thus these
are optimal locations to see if pre-conditioning and/or storm-time input are
the same or differ between the hemispheres.
In this study, we use ionosonde values of the F2-layer maximum electron
density (NmF2) to study geophysical equivalency at Wallops Island (VA) and
Hobart (Tasmania), using statistical summaries of 206 events during solar
cycle #20. We form average patterns of ΔNmF2 (%) versus local
time over 7-day storm periods that are constructed in ways that enhance the
portrayal of the average characteristic features of the positive and
negative phases of ionospheric storms. The results show a consistency
between four local time characteristic patterns of storm-induced
perturbations, and thus for the average magnitudes and time scales of the
processes that cause them in each hemisphere. Subtle differences linked to
small departures from pure geophysical equivalency point to a possible
presence of hemispheric asymmetries governed by the non-mirror-image of
geomagnetic morphology in each hemisphere. |
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