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| Titel |
Analysis of the positive ionospheric response to a moderate geomagnetic storm using a global numerical model |
| VerfasserIn |
A. A. Namgaladze, M. Forster, R. Y. Yurik |
| 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 ; 18, no. 4 ; Nr. 18, no. 4, S.461-477 |
| Datensatznummer |
250013957
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| Publikation (Nr.) |
 copernicus.org/angeo-18-461-2000.pdf |
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| Zusammenfassung |
Current theories of F-layer storms are
discussed using numerical simulations with the Upper Atmosphere Model, a global
self-consistent, time dependent numerical model of the thermosphere-ionosphere-plasmasphere-magnetosphere
system including electrodynamical coupling effects. A case study of a moderate
geomagnetic storm at low solar activity during the northern winter solstice
exemplifies the complex storm phenomena. The study focuses on positive
ionospheric storm effects in relation to thermospheric disturbances in general
and thermospheric composition changes in particular. It investigates the
dynamical effects of both neutral meridional winds and electric fields caused by
the disturbance dynamo effect. The penetration of short-time electric fields of
magnetospheric origin during storm intensification phases is shown for the first
time in this model study. Comparisons of the calculated thermospheric
composition changes with satellite observations of AE-C and ESRO-4 during storm
time show a good agreement. The empirical MSISE90 model, however, is less
consistent with the simulations. It does not show the equatorward propagation of
the disturbances and predicts that they have a gentler latitudinal gradient.
Both theoretical and experimental data reveal that although the ratio of [O]/[N2]
at high latitudes decreases significantly during the magnetic storm compared
with the quiet time level, at mid to low latitudes it does not increase (at
fixed altitudes) above the quiet reference level. Meanwhile, the ionospheric
storm is positive there. We conclude that the positive phase of the ionospheric
storm is mainly due to uplifting of ionospheric F2-region
plasma at mid latitudes and its equatorward movement at low latitudes along
geomagnetic field lines caused by large-scale neutral wind circulation and the
passage of travelling atmospheric disturbances (TADs). The calculated zonal
electric field disturbances also help to create the positive ionospheric
disturbances both at middle and low latitudes. Minor contributions arise from
the general density enhancement of all constituents during geomagnetic storms,
which favours ion production processes above ion losses at fixed height under
day-light conditions.
Key words: Atmospheric composition and structure
(thermosphere · composition and chemistry) · Ionosphere (ionosphere ·
atmosphere interactions; modelling and forecasting) |
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