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| Titel |
Localized structure in the cusp and high-latitude ionosphere: a modelling study |
| VerfasserIn |
H. F. Balmforth, R. J. Moffett, A. S. Rodger |
| 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 ; 17, no. 4 ; Nr. 17, no. 4, S.455-462 |
| Datensatznummer |
250013708
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| Publikation (Nr.) |
 copernicus.org/angeo-17-455-1999.pdf |
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| Zusammenfassung |
The ionospheric signature of a flux transfer
event (FTE) seen in EISCAT radar data has been used as the basis for a modelling
study using a new numerical model of the high-latitude ionosphere developed at
the University of Sheffield, UK. The evolution of structure in the high-latitude
ionosphere is investigated and examined with respect to the current views of
polar patch formation and development. A localized velocity enhancement, of the
type associated with FTEs, is added to the plasma as it passes through the cusp.
This is found to produce a region of greatly enhanced ion temperature. The new
model can provide greater detail during this event as it includes anisotropic
temperature calculations for the O+ ions. This illustrates the uneven
partitioning of the energy during an event of this type. O+ ion
temperatures are found to become increasingly anisotropic, with the
perpendicular temperature being substantially larger than the parallel component
during the velocity enhancement. The enhanced temperatures lead to an increase
in the recombination rate, which results in an alteration of the ion
concentrations. A region of decreased O+ and increased molecular ion
concentration develops in the cusp. The electron temperature is less enhanced
than the ions. As the new model has an upper boundary of 10 000 km the topside
can also be studied in great detail. Large upward fluxes are seen to transport
plasma to higher altitudes, contributing to the alteration of the ion densities.
Plasma is stored in the topside ionosphere and released several hours after the
FTE has finished as the flux tube convects across the polar cap. This mechanism
illustrates how concentration patches can be created on the dayside and be
maintained into the nightside polar cap.
Key words. Ionosphere (ionosphere-magnetosphere
interactions; polar ionosphere). Magnetospheric physics (magnetopause · cusp
and boundary layers) |
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