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| Titel |
Substorm correlated absorption on a 3200 km trans-auroral HF propagation path |
| VerfasserIn |
S. E. Milan, T. B. Jones, Mark Lester, E. M. Warrington, G. D. Reeves |
| 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 ; 14, no. 2 ; Nr. 14, no. 2, S.182-190 |
| Datensatznummer |
250012167
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| Publikation (Nr.) |
 copernicus.org/angeo-14-182-1996.pdf |
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| Zusammenfassung |
| A high-frequency transmitter located at Clyde
River, NWT, Canada, and a receiver located near Boston, USA, provide a 3200 km
trans-auroral, near-meridional propagation path over which the propagation
characteristics have been measured. Out of the fourteen frequencies in the HF
band sampled every hour for the duration of the experimental campaign (16
January–8 February 1989), the signal level measurements of 6.800 MHz
transmissions were selected in order to determine the extent and occurrence of
auroral absorption. The median level of auroral absorption along the path is
found to increase with geomagnetic activity, quantified by the index Kp,
with the increase being greater in the post-midnight sector than in the
pre-midnight sector. This asymmetric behaviour is attributed to the
precipitation of high energy electrons into the midnight and morning sector
auroral D region. The measured diurnal variation in the median level of
absorption is consistent with previous models describing the extent and
magnitude of auroral absorption and electron precipitation. Individual substorms,
identified from geosynchronous satellite data, are found to cause short-lived
absorption events in the HF signal level of ~30 dB at 6.800 MHz. The occurrence
of substorm correlated auroral absorption events is confined to the midnight and
morning sectors, consistent with the location of the electron precipitation. The
magnitude of absorption is related to the magnetotail stress during the substorm
growth phase and the magnetotail relaxation during the substorm expansion phase
onset. The absorption magnitude and the occurrence of substorms during the
period of the campaign increase at times of high Kp , leading
to an increase in median auroral absorption during disturbed periods. |
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