The equatorial ionospheric response over Tirunelveli to the 15 January 2010 annular solar eclipse: observations

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 <I>fo</I>F1 during the maximum phase of the eclipse. During the beginning phase of the eclipse, an enhancement of 0.97 MHz was observed in the <I>fo</I>F2 as compared to that of the control days. But the <I>fo</I>F2 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 <I>h</I>'F2 and <I>hm</I>F2 showed lower values than the control days, although <I>hm</I>F2 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).