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| Titel |
Timing and location of substorm onsets from THEMIS satellite and ground based observations |
| VerfasserIn |
S. Mende, V. Angelopoulos, H. U. Frey, E. Donovan, B. Jackel, K.-H. Glassmeier, J. P. McFadden, D. Larson, C. W. Carlson |
| 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 ; 27, no. 7 ; Nr. 27, no. 7 (2009-07-15), S.2813-2830 |
| Datensatznummer |
250016591
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| Publikation (Nr.) |
 copernicus.org/angeo-27-2813-2009.pdf |
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| Zusammenfassung |
| The unprecedented coverage of the THEMIS GBO station network coupled with
high temporal and spatial resolution allowed us to determine the various
stages of the global scale developments of the optical aurora at substorm
onsets. We identified several steps of the substorm onset auroral phenomena
and we suggest that the most rapid development is the starting of the
Substorm Poleward Expansion (SPE) and it is most useful for accurate timing
of the substorm onset. The physical significance of this step is the start
of the large scale substorm energy dissipation in the atmosphere due to
particle precipitation and auroral electrojet currents. We also recognized
several pre-cursor features. We also measured the time of arrival of
magnetic impulses associated with the same substorms at the THEMIS
satellites. We used these times and a simple model with assumed
iono-acoustic speeds in the range of 300–800 km/s to calculate the location
and time of the origin of the magnetic impulses propagating from substorm
onset. The assumption was made that the substorm occurred between two THEMIS
satellites and the impulses propagated away from a singular starting point
in and out along the magneto tail GSM-x axis. This technique is only useful
in cases where the ground based signature of the substorm is very close in
local time (or longitude) to the foot of the field lines of the THEMIS
satellites. The x distance of the calculated origins were naturally highly
dependent on the assumed propagation velocity model and the associated
magneto-sonic speed. The resulting x distances of the starting point for the
three events ranged between 11 and 17.6 RE. denoting a starting region
that requires highly stretched field lines to map to the auroral onset
latitude but which is generally considered to be too close for neutral line
formation. The corresponding start times were in the range of 0 to 170 s
prior SPE depending strongly on the assumed propagation speed. |
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