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Ann. Geophys., 21, 2323-2328, 2003
www.ann-geophys.net/21/2323/2003/
© European Geosciences Union 2003
Study of mid-latitude nighttime enhancement in F-region electron density using tomographic images over the UK
R. S. Dabas1 and L. Kersley2
1Radio and Atmospheric Sciences Division, National Physical Laboratory, New Delhi-110012, India
2Department of Physics, University of Wales, Aberystwyth, SY23, 3BZ, UK
Abstract. Nighttime enhancements in ionospheric electron content (IEC)/peak
electron density (NmF2) have been studied by various workers in the
equatorial anomaly and mid-latitude regions. Such studies give an idea about
their enhancement over that location only. In the present study tomographic
images over the UK, which give a latitudinal versus height distributions of
ionospheric electron density in a much wider area, have been used to study the
anomalous increases in nighttime F-region electron density at mid-latitudes.
From the analysis of four seasonal representative months (November 1997, March,
June and October 1998) data it was noted that the majority of the cases of
nighttime enhancements were observed after local midnight, with a maximum
between 03:00–04:00 LT in the month of November 1997. Enhancements were
observed mostly between 45–50° N latitudes, and their positions are not
affected by magnetic activity (Kp ) variations, whereas the
separation between the mid-latitude trough and enhancement decreases with
increases in magnetic activity. This finding shows that only the trough moves
equatorward with the increase in magnetic activity. It is also noted that the
electron density gradient from the trough to the enhancement increases with an
increase in Kp. Results are discussed in terms of downward plasma
transport from the protonosphere to the ionosphere and the nighttime neutral
winds.
Key words. Ionosphere (mid-latitude
ionosphere; modeling and forecasting; instruments and techniques)
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