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| Titel |
Ionospheric long-term trends: can the geomagnetic control and the greenhouse hypotheses be reconciled? |
| VerfasserIn |
A. V. Mikhailov |
| 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 ; 24, no. 10 ; Nr. 24, no. 10 (2006-10-20), S.2533-2541 |
| Datensatznummer |
250015648
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| Publikation (Nr.) |
 copernicus.org/angeo-24-2533-2006.pdf |
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| Zusammenfassung |
| The ionospheric F2-layer parameter long-term trends are considered from the
geomagnetic control concept and the greenhouse hypothesis points of view. It
is stressed that long-term geomagnetic activity variations are crucial for
ionosphere long-term trends, as they determine the basic natural pattern of
foF2 and hmF2 long-term variations. The geomagnetic activity effects should
be removed from the analyzed data to obtain real trends in ionospheric
parameters, but this is not usually done. Only a thermosphere cooling, which
is accepted as an explanation for the neutral density decrease, cannot be
reconciled with negative foF2 trends revealed for the same period. A more
pronounced decrease of the O/N2 ratio is required which is not provided by
empirical thermospheric models. Thermospheric cooling practically cannot be
seen in foF2 trends, due to a weak NmF2 dependence on neutral
temperature; therefore, foF2 trends are mainly controlled by geomagnetic activity
long-term variations. Long-term hmF2 variations are also controlled by
geomagnetic activity variations, as both parameters, NmF2 and hmF2 are related
by the F2-layer formation mechanism. But hmF2 is very sensitive to neutral
temperature changes, so strongly damped hmF2 long-term variations observed
at Slough after 1972 may be considered as a direct manifestation of the
thermosphere cooling. Earlier revealed negative hmF2 trends in western
Europe, where magnetic declination D<0 and positive trends at the eastern
stations (D>0), can be related to westward thermospheric wind whose role
has been enhanced due to a competition between the thermosphere cooling (CO2
increase) and its heating under increasing geomagnetic activity after the
end of the 1960s. |
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