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| Titel |
Time variations of the ionosphere at the northern tropical crest of ionization at Phu Thuy, Vietnam |
| VerfasserIn |
H. Pham Thi Thu, C. Amory-Mazaudier, M. Huy |
| 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 ; 29, no. 1 ; Nr. 29, no. 1 (2011-01-26), S.197-207 |
| Datensatznummer |
250016959
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| Publikation (Nr.) |
 copernicus.org/angeo-29-197-2011.pdf |
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| Zusammenfassung |
| This study is the first which gives the climatology of the ionosphere at the
northern tropical crest of ionization in the Asian sector. We use the data
from Phu Thuy station, in Vietnam, through three solar cycles (20, 21 and
22), showing the complete morphology of ionosphere parameters by analyzing
long term variation, solar cycle variation and geomagnetic activity effects,
seasonal evolution and diurnal development. Ionospheric critical
frequencies, foF2, foF1 and foE, evolve according to the 11-year sunspot cycle.
Seasonal variations show that foF2 exhibits a semiannual pattern with maxima
at equinox, and winter and equinoctial anomalies depending on the phases of
the sunspot solar cycle. ΔfoF2 exhibits a semiannual variation during
the minimum phase of the sunspot solar cycle 20 and the increasing and
decreasing phases of solar cycle 20, 21 and 22. ΔfoF1 exhibits an
annual variation during the maximum phase of solar cycles 20, 21 and 22.
Δh'F2 shows a regular seasonal variation for the different solar
cycles while Δh'F1 exhibits a large magnitude dispersion from one
sunspot cycle to another. The long term variations consist in an increase of
1.0 MHz for foF2 and of 0.36 MHz for foF1. foE increases 0.53 MHz from solar
cycle 20 to solar cycle 21 and then decreases −0.23 MHz during the
decreasing phase of cycle 21. The diurnal variation of the critical
frequency foF2 shows minima at 05:00 LT and maxima around 14:00 LT. foF1 and
foE have a maximum around noon. The diurnal variation of h'F2 exhibits a
maximum around noon. The main features of h'F1 are a minimum near noon and
the maximum near midnight. Other minima and maxima occur in the morning, at
about 04:00 or 05:00 LT and in the afternoon, at about 18:00 or 19:00 LT but
they are markedly smaller. Only during the maximum phase of all sunspot
solar cycles the maximum near 19:00 LT is more pronounced. |
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