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| Titel |
GPS observations of medium-scale traveling ionospheric disturbances over Europe |
| VerfasserIn |
Y. Otsuka, K. Suzuki, S. Nakagawa, M. Nishioka, K. Shiokawa, T. Tsugawa |
| 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 ; 31, no. 2 ; Nr. 31, no. 2 (2013-02-05), S.163-172 |
| Datensatznummer |
250017747
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| Publikation (Nr.) |
 copernicus.org/angeo-31-163-2013.pdf |
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| Zusammenfassung |
| Two-dimensional structures of medium-scale traveling ionospheric disturbances
(MSTIDs)
over Europe have been revealed, for the first time,
by using maps of the total electron content (TEC) obtained from
more than 800 GPS receivers of the European GPS receiver networks.
From statistical analysis of the TEC maps
obtained 2008, we have found that
the observed MSTIDs can be categorized into two groups: daytime MSTID
and nighttime MSTID. The daytime MSTID frequently occurs in winter.
Its maximum occurrence rate in monthly and hourly bin exceeds 70%
at lower latitudes over Europe, whereas
it is approximately 45% at higher latitudes.
Since most of the daytime MSTIDs propagate southward,
we speculate that they could be caused by atmospheric gravity waves in the thermosphere.
The nighttime MSTIDs also frequently occur in winter but most of them
propagate southwestward, in a direction consistent with the theory that polarization electric fields play an important role in generating the nighttime MSTIDs.
The nighttime MSTID occurrence rate shows distinct
latitudinal difference:
The maximum of the occurrence rate in monthly and hourly bin
is approximately 50% at lower latitudes in Europe,
whereas the nighttime MSTID was rarely observed
at higher latitudes.
We have performed model calculations of the plasma density perturbations
caused by a gravity wave and an oscillating electric field to reproduce
the daytime and nighttime MSTIDs, respectively.
We find that TEC perturbations caused by
gravity waves do not show dip angle dependencies,
while those caused by the oscillating electric field
have a larger amplitude at lower latitudes.
These dip angle dependencies of the TEC perturbation amplitude could
contribute to
the latitudinal variation of the MSTID occurrence rate.
Comparing with previous studies,
we discuss the longitudinal difference of the nighttime MSTID occurrence
rate, along with the E- and F-region coupling processes.
The seasonal variation, of the nighttime MSTID occurrence rate in Europe,
is not consistent with the theory that
the longitudinal and seasonal variations of the nighttime MSTID occurrence
could be attributed to those of the Es layer occurrence. |
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