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| Titel |
Annual and seasonal variations in the low-latitude topside ionosphere |
| VerfasserIn |
Y. Z. Su, G. J. Bailey, K.-I. Oyama |
| 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 ; 16, no. 8 ; Nr. 16, no. 8, S.974-985 |
| Datensatznummer |
250013394
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| Publikation (Nr.) |
 copernicus.org/angeo-16-974-1998.pdf |
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| Zusammenfassung |
| Annual and seasonal variations in the
low-latitude topside ionosphere are investigated using observations made by the
Hinotori satellite and the Sheffield University Plasmasphere Ionosphere Model
(SUPIM). The observed electron densities at 600 km altitude show a strong annual
anomaly at all longitudes. The average electron densities of conjugate latitudes
within the latitude range ±25° are higher at the December solstice than at the
June solstice by about 100 during daytime and 30 during night-time. Model
calculations show that the annual variations in the neutral gas densities play
important roles. The model values obtained from calculations with inputs for the
neutral densities obtained from MSIS86 reproduce the general behaviour of the
observed annual anomaly. However, the differences in the modelled electron
densities at the two solstices are only about 30 of that seen in the observed
values. The model calculations suggest that while the differences between the
solstice values of neutral wind, resulting from the coupling of the neutral gas
and plasma, may also make a significant contribution to the daytime annual
anomaly, the E×B drift velocity may slightly weaken the annual
anomaly during daytime and strengthen the anomaly during the post-sunset period.
It is suggested that energy sources, other than those arising from the 6
difference in the solar EUV fluxes at the two solstices due to the change in the
Sun-Earth distance, may contribute to the annual anomaly. Observations show
strong seasonal variations at the solstices, with the electron density at 600 km
altitude being higher in the summer hemisphere than in the winter hemisphere,
contrary to the behaviour in NmF2. Model calculations confirm that the seasonal
behaviour results from effects caused by transequatorial component of the
neutral wind in the direction summer hemisphere to winter hemisphere. |
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