dc.contributor.author |
Sastri, J. H |
|
dc.date.accessioned |
2008-09-06T11:23:32Z |
|
dc.date.available |
2008-09-06T11:23:32Z |
|
dc.date.issued |
1999-08 |
|
dc.identifier.citation |
Annales Geophysicae, Vol. 17, No. 8, pp. 1111 - 1115 |
en |
dc.identifier.issn |
0992-7689 |
|
dc.identifier.uri |
http://hdl.handle.net/2248/3420 |
|
dc.description.abstract |
At dip equatorial stations in the Indian zone, spread-F conditions are known to develop preferentially around midnight during the June solstice (northern summer) months of low solar activity, in association with a distinct increase in F layer height. It is currently held that this onset of spread-F far away from the sunset terminator is due to the generalised Rayleigh-Taylor instability mechanism, with the gravitational and cross-field instability factors (and hence F layer height) playing important roles. We have studied the quarter-hourly ionograms of Kodaikanal (10.2°N; 77.5°E; dip 4°N) for the northern summer months (May-August) of 1994 and 1995 to ascertain the ambient ionospheric conditions against which the post-midnight onset of spread-F takes place. A data sample of 38 nights with midnight onset of spread-F and 34 nights without spread-F is used for the purpose. It is found that a conspicious increase in F layer height beginning around 2100 LT occurs on nights with spread-F as well as without spread-F. This feature is seen in the nocturnal pattern of F layer height on many individual nights as well as of average F layer height for the two categories of nights. The result strongly suggests that the F layer height does not play a pivotal role in the midnight onset of spread-F during the June solstice of solar minimum. The implications of this finding are discussed. |
en |
dc.language.iso |
en |
en |
dc.publisher |
European Geosciences Union |
en |
dc.relation.uri |
http://adsabs.harvard.edu/abs/1999AnGeo..17.1111S |
en |
dc.relation.uri |
http://www.ann-geophys.net/17/1111/1999/angeo-17-1111-1999.html |
en |
dc.subject |
Ionosphere (equatorial ionosphere; ionospheric irregularities) |
en |
dc.title |
Post-midnight onset of spread-F at Kodaikanal during the June solstice of solar minimum |
en |
dc.type |
Article |
en |