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| Titel |
F-region ionospheric perturbations in the low-latitude ionosphere during the geomagnetic storm of 25-27 August 1987 |
| VerfasserIn |
A. V. Pavlov, S. Fukao, S. Kawamura |
| 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 ; 22, no. 10 ; Nr. 22, no. 10 (2004-11-03), S.3479-3501 |
| Datensatznummer |
250015025
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| Publikation (Nr.) |
 copernicus.org/angeo-22-3479-2004.pdf |
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| Zusammenfassung |
| We have presented a comparison between the modeled NmF2 and
hmF2, and NmF2 and hmF2 which were observed at the equatorial anomaly crest
and close to the geomagnetic equator simultaneously by the Akita, Kokubunji,
Yamagawa, Okinawa, Manila, Vanimo, and Darwin ionospheric sounders and by
the middle and upper atmosphere (MU) radar (34.85° N, 136.10° E)
during the 25-27 August 1987 geomagnetically storm-time period at low solar
activity near 201°, geomagnetic longitude. A comparison between the
electron and ion temperatures measured by the MU radar and those produced by
the model of the ionosphere and plasmasphere is presented. The corrections
of the storm-time zonal electric field, EΛ, from 16:30 UT to
21:00 UT on 25 August bring the modeled and measured hmF2 into reasonable
agreement. In both hemispheres, the meridional neutral wind, W, taken from
the HWW90 wind model and the NRLMSISE-00 neutral temperature, Tn, and
densities are corrected so that the model results agree with the ionospheric
sounders and MU radar observations. The geomagnetic latitude variations in
NmF2 on 26 August differ significantly from those on 25 and 27 August. The
equatorial plasma fountain undergoes significant inhibition on 26 August.
This suppression of the equatorial anomaly on 26 August is not due to a
reduction in the meridional component of the plasma drift perpendicular to
the geomagnetic field direction, but is due to the action of storm-time
changes in neutral winds and densities on the plasma fountain process. The
asymmetry in W determines most of the north-south asymmetry in hmF2 and NmF2
on 25 and 27 August between about 01:00-01:30 UT and about 14:00 UT when the
equatorial anomaly exists in the ionosphere, while asymmetries in W,
Tn, and neutral densities relative to the geomagnetic equator are
responsible for the north-south asymmetry in NmF2 and hmF2 on 26 August. A
theory of the primary mechanisms causing the morning and evening peaks in
the electron temperature, Te, is developed. An appearance, magnitude
variations, latitude variations, and a disappearance of the morning Te
peaks during 25-27 August are caused by variations in EΛ,
thermospheric composition, Tn, and W. The magnitude of the evening
Te peak and its time location are decreased with the lowering of the
geomagnetic latitude due to the weakening of the effect of the plasma drift
caused by W on the electron density. The difference between 25 August and
26-27 August in an appearance, magnitude and latitude variations, and a
disappearance of the evening Te peak is caused by variations in W, the
thermospheric composition, Tn, and EΛ. |
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