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| Titel |
Solar cycle dependent characteristics of the equatorial blanketing Es layers and associated irregularities |
| VerfasserIn |
C. V. Devasia, V. Sreeja, S. Ravindran |
| 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 ; 24, no. 11 ; Nr. 24, no. 11 (2006-11-21), S.2931-2947 |
| Datensatznummer |
250015677
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| Publikation (Nr.) |
 copernicus.org/angeo-24-2931-2006.pdf |
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| Zusammenfassung |
| The occurrence of blanketing type Es (Esb) layers and associated
E-region irregularities over the magnetic equatorial location of Trivandrum
(8.5° N; 77° E; dip ~0.5°) during the summer solstitial
months of May, June, July and August has been investigated in detail for the
period 1986–2000 to bring out the variabilities in their characteristics
with the solar cycle changes. The study has been made using the ionosonde
and magnetometer data of Trivandrum from 1986–2000 along with the available
data from the 54.95 MHz VHF backscatter radar at Trivandrum for the period
1995–2000. The appearance of blanketing Es layers during these months
is observed to be mostly in association with the occurrence of afternoon
Counter Electrojet (CEJ) events. The physical process leading to the
occurrence of a CEJ event is mainly controlled by the nature of the
prevailing electro dynamical/neutral dynamical conditions before the event.
Hence it is natural that the Esb layer characteristics like the
frequency of occurrence, onset time, intensity, nature of gradients in its
top and bottom sides etc are also affected by the nature of the background
electro dynamical /neutral dynamical processes which in turn are strongly
controlled by the solar activity changes. The occurrence of Esb layers
during the solstitial months is found to show very strong solar activity
dependence with the occurrence frequency being very large during the solar
minimum years and very low during solar maximum years. The intensity of the
VHF radar backscattered signals from the Esb irregularities is observed
to be controlled by the relative roles of the direction and magnitude of the
prevailing vertical polarization electric field and the vertical electron
density gradient of the prevailing Esb layer depending on the phase of
the solar cycle. The gradient of the Esb layer shows a more dominant
role in the generation of gradient instabilities during solar minimum
periods while it is the electric field that has a more dominant role during
solar maximum periods. |
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