Abstract
Abstract. In this paper we present a case study of the annular solar eclipse effects on the ionization of E and F regions of equatorial ionosphere over Tirunelveli [77.8° E, 8.7° N, dip 0.4° N] by means of digital ionosonde on 15 January 2010. The maximum obscuration of the eclipse at this station was 84% and it occurred in the afternoon. The E and F1 layers of the ionosphere showed very clear decrease in their electron concentrations, whereas the F2 layer did not show appreciable changes. A reduction of 30% was observed in the foF1 during the maximum phase of the eclipse. During the beginning phase of the eclipse, an enhancement of 0.97 MHz was observed in the foF2 as compared to that of the control days. But the foF2 decreased gradually as the eclipse progressed and a decrease of 0.59 MHz was observed towards the end phase of the eclipse. Observed variations in the h'F2 and hmF2 showed lower values than the control days, although hmF2 was found to increase a bit during the eclipse. Observed variability in the E, F1 and F2 layer ionospheric parameters on the eclipse day and their departure from the control days are discussed as the combined effect of annular eclipse and presence of counter equatorial electrojet (CEEJ).
Highlights
A solar eclipse provides an excellent opportunity to explore the upper and lower ionospheric effects associated with an accurately estimated variation of solar radiation during the eclipse period
Both the measurements and simulations show that the eclipse effect is larger in the midday than in the morning and afternoon, and the decrease in electron concentration is greater in the F1 region than in the E region (Le at al., 2008a)
We find that the decrease in electron density occurs throughout the E and F1 layer heights at about the same time, while, in the F2 region, the electron density decrease began at lower heights and extended progressively towards the layer peak
Summary
A solar eclipse provides an excellent opportunity to explore the upper and lower ionospheric effects associated with an accurately estimated variation of solar radiation during the eclipse period. Study of the ionospheric response to a solar eclipse has been in place for decades, and extensive studies have been made with various experimental techniques, such as ionosondes, incoherent scatter radar, rockets, Faraday rotation measurements, global positioning system and satellite measurements (Evans, 1965a, b; Klobuchar and Whitney, 1965; Rishbeth, 1968; Hunter et al, 1974; Oliver and Bowhill, 1974; Cohen, 1984; Salah et al, 1986; Cheng et al, 1992; Farges et al, 2001; Tomas et al, 2007) as well as theoretical modeling (Le at al., 2008a, and references therein) Both the measurements and simulations show that the eclipse effect is larger in the midday than in the morning and afternoon, and the decrease in electron concentration is greater in the F1 region than in the E region (Le at al., 2008a). The details of the eclipse are available at http://eclipse.gsfc.nasa.gov/SEmono/ ASE2010/ASE2010.html
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