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| Titel |
Steep latitudinal gradients of thermospheric composition during magnetic storms: a possible formation mechanism |
| VerfasserIn |
M. G. Skoblin, M. Forster |
| 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 ; 13, no. 3 ; Nr. 13, no. 3, S.277-284 |
| Datensatznummer |
250011787
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| Publikation (Nr.) |
 copernicus.org/angeo-13-277-1995.pdf |
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| Zusammenfassung |
| Mass spectrometer satellite observations show
that a narrow region with steep latitudinal gradients of neutral composition is
formed in the subauroral winter thermosphere during magnetic storms. In order to
analyze the relative importance of individual terms in the continuity equation
for atomic oxygen, a two-dimensional model was used to simulate the
thermospheric disturbance formation in response to intense Joule heating imposed
in the auroral oval. Such an approach allowed three characteristic zones to be
distinguished in the high-latitude thermosphere at heights of about 250 km. It
was shown that vertical transport is of greatest importance within the local
heating region. Horizontal transport dominates at subauroral latitudes near the
mid-night edge of the auroral oval. Propagation of the disturbances to middle
latitudes is prohibited near the noon edge of the oval by a strong counteraction
of a poleward meridional wind. Here is a "relaxation zone" defined as
the region which is spread to the equator from the boundary between the local
heating area and the subauroral zone in the noon sector LT. It is at this
boundary that composition distributions with steep latitudinal gradient are
formed within the first few hours of Joule heating source action. Perturbations
transported to middle latitudes during the periods when the meridional wind is
directed equatorward begin to relax in this zone with a characteristic time
scale of about 7 h, independent of season. However, in winter, composition at
subauroral latitudes recovers to unperturbed N2/O values before the
wind again turns equatorward, giving rise to a distribution with steep
latitudinal gradient recovering. In summer, a complete relaxation cannot be
reached due to a shorter time interval with poleward wind and a larger
disturbance amplitude. These two factors result in an effective smoothing of the
initial steep gradient and a more regular latitudinal distribution of
composition is observed in the summer thermosphere. |
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