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| Titel |
Topside equatorial zonal ion velocities measured by C/NOFS during rising solar activity |
| VerfasserIn |
W. R. Coley, R. A. Stoneback, R. A. Heelis, M. R. Hairston |
| 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 ; 32, no. 2 ; Nr. 32, no. 2 (2014-02-04), S.69-75 |
| Datensatznummer |
250121020
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| Publikation (Nr.) |
 copernicus.org/angeo-32-69-2014.pdf |
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| Zusammenfassung |
| The Ion Velocity Meter (IVM), a part of the Coupled Ion Neutral Dynamic
Investigation (CINDI) instrument package on the Communication/Navigation
Outage Forecast System (C/NOFS) spacecraft, has made over 5 yr of
in situ measurements of plasma temperatures, composition, densities, and
velocities in the 400–850 km altitude range of the equatorial ionosphere.
These measured ion velocities are then transformed into a coordinate system
with components parallel and perpendicular to the geomagnetic field allowing
us to examine the zonal (horizontal and perpendicular to the geomagnetic
field) component of plasma motion over the 2009–2012 interval. The general
pattern of local time variation of the equatorial zonal ion velocity is well
established as westward during the day and eastward during the night, with
the larger nighttime velocities leading to a net ionospheric superrotation.
Since the C/NOFS launch in April 2008, F10.7 cm radio fluxes have gradually
increased from around 70 sfu to levels in the 130–150 sfu range. The
comprehensive coverage of C/NOFS over the low-latitude ionosphere allows us
to examine variations of the topside zonal ion velocity over a wide level of
solar activity as well as the dependence of the zonal velocity on apex
altitude (magnetic latitude), longitude, and solar local time. It was found
that the zonal ion drifts show longitude dependence with the largest net
eastward values in the American sector. The pre-midnight zonal drifts show
definite solar activity (F10.7) dependence. The daytime drifts have a lower
dependence on F10.7. The apex altitude (magnetic latitude) variations
indicate a more westerly flow at higher altitudes. There is often a net
topside subrotation at low F10.7 levels, perhaps indicative of a suppressed
F region dynamo due to low field line-integrated conductivity and a low
F region altitude at solar minimum. |
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