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Ann. Geophys., 21, 745-750, 2003
www.ann-geophys.net/21/745/2003/
© European Geosciences Union 2003
Post midnight spread-F occurrence over Waltair (17.7° N, 83.3° E) during low and ascending phases of solar activity
K. Niranjan, P. S. Brahmanandam, P. Ramakrishna Rao, G. Uma, D. S. V. V. D. Prasad, and P. V. S. Rama Rao
Department of Physics, Andhra University, Visakhapatnam 530 003, India
Abstract. A study carried out on
the occurrence of post midnight spread-F events at a low-latitude station,
Waltair (17.7° N, 83.3° E), India revealed that its occurrence is maximum in
the summer solstice months of the low solar activity period and decreases with
an increase in the sunspot activity. The F-region virtual height variations
show that 80% of these spread-F cases are associated with an increase in the
F-region altitude. It is suggested with the support of the night airglow 6300 A
zenith intensity data obtained with co-located ground-based night airglow
photometer and electron temperature data from the Indian SROSS C2 satellite
that the seasonal variation of the occurrence and probable onset times of the
post midnight spread-F depend on the characteristics of the highly variable
semipermanent equatorial Midnight Temperature Maximum (MTM).
Key words. Ionosphere (ionospheric
irregularities; ionosphere atmosphere interactions) Atmospheric composition and
structure (airglow and Aurora)
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