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| Titel |
Multi-wavelength imaging observations of plasma depletions over Kavalur, India |
| VerfasserIn |
H. S. S. Sinha, P. K. Rajesh, R. N. Misra, N. Dutt |
| 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 ; 19, no. 9 ; Nr. 19, no. 9, S.1119-1131 |
| Datensatznummer |
250014321
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| Publikation (Nr.) |
 copernicus.org/angeo-19-1119-2001.pdf |
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| Zusammenfassung |
Observations of
ionospheric plasma depletions were made over Kavalur (12.56° N, 78.8° E, Mag.
Lat 4.6° N), India during March–pril 1998 using an all sky optical imaging
system operating at 630 nm, 777.4 nm and 557.7 nm. Out of 14 nights of
observations, plasma depletions were seen only on 9 nights. Except for 21 March
1998, which was a magnetically disturbed period, all other nights belonged to a
magnetically quiet period. Some of the important results obtained from these
observations are: (a) After the onset of the equatorial spread F (ESF), plasma
depletions take typically about 2 hrs 40 min to come to a fully developed
state, (b) There are three distinct types of plasma depletions: type 1 have an
east-west (e–w) extent of 250–350 km with an inter-depletion distance (IDD) of
125–300 km; Type 2 have an e–w extent of 100–150 km and IDD of 50–150 km; Type
3 have smallest the e–w extent (40–100 km) and IDD of 20–60 km, (c) Most of the
observed plasma depletions (> 82%) had their eastward velocity in the range
of 25–125 ms–1. Almost stationary plasma depletions (0–25 ms–1)
were observed on one night, which was magnetically disturbed. These very slow
moving depletions appear to be the result of a modification of the F-region
dynamo field due to direct penetration of the electric field and/or changes in
the neutral winds induced by the magnetic disturbance, (d) On the night of
21/22 March 1998, which was a magnetically disturbed period, plasma depletions
could be seen simultaneously in all three observing wavelengths, i.e. in 630
nm, 777.4 nm and 557.7 nm. It is believed that this simultaneous occurrence was
due to neutral density modifications as a result of enhanced magnetic activity.
(e) Well developed brightness patterns were observed for the first time in
777.4 nm images. Earlier, such brightness patterns were observed only in 630 nm
and 557.7 nm images. These brightness patterns initially appear as very small
regions in the northern part of the image and then in about 90 min time, they
attain their peak brightness and encompass the entire field-of-view in about 2
hrs 30 min. In some cases, brightness patterns contain one or two well
developed plasma depletions within them. (f) The brightness patterns reported
here differ from the earlier observations in that they do not show any
differential behaviour in the direction of movement before and after the
midnight, and that they are present for extended periods of time as large as 6
hrs.
Key words. Atmospheric composition
and structure (air-glow and aurora); Ionosphere (equatorial ionosphere;
ionospheric irregularities) |
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