Presunrise spread F at Fortaleza

At Fortaleza, Brazil, in the equatorial zone about 400 km south of the magnetic equator a presunrise (secondary) maximum of spread F occurrence is observed during sunspot minimum and, in particular, during December solstice. The spread F takes the form of patches of irregularities that are convectin...

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Bibliographic Details
Published in:Journal of Geophysical Research, Washington, DC Washington, DC, 1998-10, Vol.103 (A10), p.23415-23425
Main Authors: MacDougall, J. W., Abdu, M. A., Jayachandran, P. T., Cecile, J.‐F., Batista, I. S.
Format: Article
Language:English
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Summary:At Fortaleza, Brazil, in the equatorial zone about 400 km south of the magnetic equator a presunrise (secondary) maximum of spread F occurrence is observed during sunspot minimum and, in particular, during December solstice. The spread F takes the form of patches of irregularities that are convecting eastwards at ∼50 m s−1. Most of the patches are collocated with bottomside bulges of the ionosphere. Our measurements indicate that these bottomside bulges are unstable due to a gradient‐drift instability that is slowly growing and produces the spread F. The bulges themselves seem to be evidence of a Rayleigh‐Taylor instability process.
ISSN:0148-0227
2156-2202
DOI:10.1029/98JA01949