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| Titel |
Features of annual and semiannual variations derived from the global ionospheric maps of total electron content |
| VerfasserIn |
B. Zhao, W. Wan, L. Liu, T. Mao, Z. Ren, M. Wang, A. B. Christensen |
| 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 ; 25, no. 12 ; Nr. 25, no. 12 (2008-01-02), S.2513-2527 |
| Datensatznummer |
250015958
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| Publikation (Nr.) |
 copernicus.org/angeo-25-2513-2007.pdf |
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| Zusammenfassung |
| In the present work we use the NASA-JPL global
ionospheric maps of total electron content (TEC), firstly to construct TEC
maps (TEC vs. magnetic local time MLT, and magnetic latitude MLAT) in the
interval from 1999 to 2005. These TEC maps were, in turn, used to estimate the
annual-to-mean amplitude ratio, A1, and the semiannual-to-mean
amplitude ratio, A2, as well as the latitudinal symmetrical and
asymmetrical parts, A' and A" of A1.
Thus, we investigated in detail the TEC climatology from maps of these
indices, with an emphasis on the quantitative presentation for local time
and latitudinal changes in the seasonal, annual and semiannual anomalies of
the ionospheric TEC. Then we took the TEC value at 14:00 LT to examine
various anomalies at a global scale following the same procedure. Results
reveal similar features appearing in NmF2, such as that the seasonal anomaly is
more significant in the near-pole regions than in the far-pole regions and
the reverse is true for the semiannual anomaly; the winter anomaly has least a chance
to be observed at the South America and South Pacific areas. The most
impressive feature is that the equinoctial asymmetry is most prominent at
the East Asian and South Australian areas. Through the analysis of the TIMED
GUVI columnar [O/N2] data, we have investigated to what extent the seasonal,
annual and semiannual variations can be explained by their counterparts in
[O/N2]. Results revealed that the [O/N2] variation is a major contributor to
the daytime winter anomaly of TEC, and it also contributes to some of the
semiannual and annual anomalies. The contribution to the anomalies
unexplained by the [O/N2] data could possibly be due to the dynamics
associated with thermospheric winds and electric fields. |
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