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| Titel |
On the occurrence and motion of decametre-scale irregularities in the sub-auroral, auroral, and polar cap ionosphere |
| VerfasserIn |
M. L. Parkinson, J. C. Devlin, H. Ye, C. L. Waters, P. L. Dyson, A. M. Breed, R. J. Morris |
| 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 ; 21, no. 8 ; Nr. 21, no. 8, S.1847-1868 |
| Datensatznummer |
250014682
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| Publikation (Nr.) |
 copernicus.org/angeo-21-1847-2003.pdf |
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| Zusammenfassung |
The statistical
occurrence of decametre-scale ionospheric irregularities, average line-of-sight
(LOS) Doppler velocity, and Doppler spectral width in the sub-auroral, auroral,
and polar cap ionosphere ( - 57°L to - 88°L)
has been investigated using echoes recorded with the Tasman International
Geospace Environment Radar (TIGER), a SuperDARN radar located on Bruny Island,
Tasmania (147.2° E, 43.4° S geographic; - 54.6 °L).
Results are shown for routine soundings made on the magnetic meridian beam 4
and the near zonal beam 15 during the sunspot maximum interval December 1999 to
November 2000. Most echoes were observed in the nightside ionosphere, typically
via 1.5-hop propagation near dusk and then via 0.5-hop propagation during
pre-midnight to dawn. Peak occurrence rates on beam 4 were often > 60% near
magnetic midnight and ~ - 70 °L. They increased and
shifted equatorward and toward pre-midnight with increasing Kp (i.e. Bz
southward). The occurrence rates remained very high for Kp > 4,
de-spite enhanced D-region absorption due to particle precipitation. Average
occurrence rates on beam 4 exhibited a relatively weak seasonal variation,
consistent with known longitudinal variations in auroral zone magnetic activity
(Basu, 1975). The average echo power was greatest between 23 and 07 MLT. Two
populations of echoes were identified on both beams, those with low spectral
width and a mode value of ~ 9 ms-1 (bin size of 2 ms-1)
concentrated in the auroral and sub-auroral ionosphere (population A), and
those with high spectral width and a mode value of ~ 70 ms-1
concentrated in the polar cap ionosphere (population B). The occurrence of
population A echoes maximised post-midnight because of TIGER’s lower
latitude, but the subset of the population A echoes observed near dusk had
characteristics reminiscent of "dusk scatter" (Ruohoniemi et al.,
1988). There was a dusk "bite out" of large spectral widths between ~
15 and 21 MLT and poleward of - 67 °L, and a
pre-dawn enhancement of large spectral widths between ~ 03 and 07 MLT,
centred on ~ - 61 °L. The average LOS Doppler
velocities revealed that frequent westward jets of plasma flow occurred
equatorward of, but overlapping, the diffuse auroral oval in the pre-midnight
sector.
Key words. Ionosphere (auroral
ionosphere; electric fields and currents, ionospheric irregularities) |
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