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| Titel |
Effect of solar and magnetic activity on VHF scintillations near the equatorial anomaly crest |
| VerfasserIn |
R. P. Singh, R. P. Patel, A. K. Singh |
| 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 ; 22, no. 8 ; Nr. 22, no. 8 (2004-09-07), S.2849-2860 |
| Datensatznummer |
250014970
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| Publikation (Nr.) |
 copernicus.org/angeo-22-2849-2004.pdf |
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| Zusammenfassung |
| The VHF amplitude scintillation recorded during the period January 1991 to
December 1993 in the declining phase of a solar cycle and April 1998 to December 1999 in
the ascending phase of the next solar cycle at Varanasi (geogr. lat.=25.3°,
long.=83.0°, dip=37°N) have been analyzed to
study the behavior of ionospheric irregularities during active solar periods
and magnetic storms. It is shown that irregularities occur at arbitrary
times and may last for <30min. A rise in solar activity increases
scintillations during winter (November-February) and near equinoxes
(March-April; September-October), whereas it depresses the scintillations
during the summer (May-July). In general, the role of magnetic activity is to
suppress scintillations in the pre-midnight period and to increase it in the
post-midnight period during equinox and winter seasons, whilst during summer
months the effect is reversed. The pre-midnight scintillation is sometimes
observed when the main phase of Dst corresponds to the pre-midnight period.
The annual variation shows suppression of scintillations on disturbed days,
both during pre-midnight and post-midnight period, which becomes more
effective during years of high solar activity. It is observed that for
magnetic storms for which the recovery phase starts post-midnight, the
probability of occurrence of irregularities is enhanced during this time. If
the magnetic storm occurred during daytime, then the probability of
occurrence of scintillations during the night hours is decreased. The
penetration of magnetospheric electric fields to the magnetic equator
affects the evolution of low-latitude irregularities. A delayed disturbance
dynamo electric field also affects the development of irregularities. |
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