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| Titel |
Ionospheric variations over Indian low latitudes close to the equator and comparison with IRI-2012 |
| VerfasserIn |
P. Pavan Chaitanya, A. K. Patra, N. Balan, S. V. B. Rao |
| 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 ; 33, no. 8 ; Nr. 33, no. 8 (2015-08-13), S.997-1006 |
| Datensatznummer |
250121233
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| Publikation (Nr.) |
 copernicus.org/angeo-33-997-2015.pdf |
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| Zusammenfassung |
| In this paper, we analyze daytime observations of the critical frequencies
of the F2 (foF2) and F3 (foF3) layers based on ionosonde observations made from
Indian low latitudes close to the magnetic equator and study their local
time, seasonal, planetary-scale variations (including the solar rotation effect),
and solar activity dependence. Given the occurrence of the F3 layer, which has remarkable local time, seasonal and solar activity dependences, variations in foF2 have been evaluated.
Local time
variations in foF2 and foF3 show noon "bite-out" in all seasons and in all
solar activity conditions, which are attributed to vertically upward plasma
transport by the zonal electric field and meridional neutral wind. Comparison of
observed foF2 with those of the IRI-2012 model clearly shows that the model
values are always higher than observed values and the largest difference is
observed during noontime owing to the noon bite-out phenomenon. Peak frequency of the
F layer (foF2 / foF3), however, is found to have better agreement with
IRI-2012 model. Seasonal variations of foF2 and foF3 show stronger asymmetry
at the solstices than at the equinoxes. The strong asymmetry at the solstice is
attributed to the asymmetry in the meridional neutral wind with a
secondary contribution from E × B drifts, and the relatively
weak asymmetry observed at the equinox is attributed to the asymmetry in
E × B drifts. Variations in foF2 and foF3
with solar flux clearly show the saturation effect when F10.7 exceeds
~ 120 sfu, which is different from that of the mid-latitudes.
Irrespective of solar flux, both foF2 and foF3 in summer, however, are found
to be remarkably lower than those observed in other seasons. Variations in
foF2 show dominant periods of ~ 27, ~ 16 and ~ 6 days. Intriguingly, amplitudes of ~ 27-day variations in foF2 are found to be maximum in low solar activity
(LSA), moderate in medium solar activity (MSA) and minimum in high solar
activity (HSA), while the amplitudes of ~ 27-day variations in
F10.7 are minimum in LSA, moderate in MSA and maximum in HSA. These
results are presented and discussed in light of current observational
and model-based knowledge on the variations of low-latitude foF2 and foF3. |
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