Ionospheric measurements during the total solar eclipse of 11 August 1999

Abstract

A number of radio experiments were conducted at Ahmedabad (23• N, 73• E) with the aim of studying the ionospheric effects of the total solar eclipse of 11 August 1999. Rapid radio soundings from the ionosonde were made on the eclipse day and on control days. A riometer was operating at 30 MHz, and Àeld strength measurements along the three oblique incidence paths of Colombo-Ahmedabad (11905 kHz), Bombay-Ahmedabad (558 kHz) and Rajkot-Ahmedabad (810 kHz) were also made. A reduction of about 20% was observed in the minimum frequency of reÁection from the ionosonde (f min ), which indicates a reduction in D-region ionization. The critical frequency of the E-layer was not measurable beyond 1600 h IST on eclipse day due to the strong blanketing sporadic-E, but there is a 20% decrease in the critical frequency of the F 1 -layer. Although there was no change in the minimum virtual height of the F-layer on eclipse day, there appears to have been a decrease in the height of maximum ionization (h p F 2 ) during the eclipse, indicating a reduction in the thickness of the F-layer. The signal strength of the Colombo-Ahmedabad path shows an initial rapid increase with the start of the eclipse (indication of a decrease in ionization in the D-and lower E-regions), but subsequently decreases until the maximum of the eclipse (excessive deviative absorption because of the wave penetrating to the E-region). The Àeld strength measurements of the Bombay-Ahmedabad path show a large fading after sunset as the sky wave also appeared. On eclipse day the fading started about an hour earlier. Riometer recordings also show a higher signal during eclipse day, which again indicates an eclipse-associated decrease in ionization.

Total solar eclipse of July 22, 2009: Its impact on the total electron content and ionospheric electron density in the Indian zone

“…This is the reason that the TEC values on the eclipse day are appreciably lower than the mean quiet day values in the peninsular India. Although, our results are in agreement with the previously reported decreasing trend of the TEC and ionospheric electron density during various solar eclipses in low (Chandra et al, 1980(Chandra et al, , 1981(Chandra et al, , 2007Vyas et al, 1997;Yeh et al, 1997;Huang et al, 1999;Tsai and Liu, 1999) and mid-latitudes (Boitman et al, 1999;Afraimovich et al, 1998Afraimovich et al, , 2002Jakowski et al, 2008;Krankowski et al, 2008) observed at different times of the day; importance of our work lies in the fact that comparable reductions in TEC and electron density are seen even during early morning eclipse.…”

“…The electron density profile on the eclipse day shows reduced electron density in the height range 100-800 km. In an earlier work (Chandra et al, 2007), reduction of the F region electron density has been mentioned in connection with the eclipse of August 1999 in the Indian zone.…”

“…Thus, during the solar eclipse, lower electron density in the ionosphere is expected. Works by Chandra et al (1980Chandra et al ( , 1981Chandra et al ( , 1997Chandra et al ( , 2007, Vyas et al (1997) and Boitman et al (1999) for example, show decrease in ionospheric electron density during the solar eclipses. Theoretical investigations of the effects of the eclipse on ionospheric E and F regions were made by Rishbeth (1968).…”

Ionospheric response to total solar eclipse of 22 July 2009 in different Indian regions

“…, for the annular solar eclipse of 15 January 2010, showed a reduction of 20 % in the total electron content at Bangalore. The decreasing trends of the ionospheric electron density and total electron content have been reported for different solar eclipse from low latitudes (Chandra et al, 1980(Chandra et al, , 1981(Chandra et al, , 2007Vyas et al, 1997;Yeh et al, 1997), but the importance of present study lies in the fact that comparable reductions in TEC have been observed at four places located on different latitudes and longitudes. The ionization density and the total electron content in the ionosphere at any given altitude depend on various phenomena such as production and loss rates involving chemical reactions and transport phenomena involving diffusion and drifts.…”

The total solar eclipse of March 2006: overview

“…The decrease in the ionization in most ionospheric layers (D, E, F1) is obvious, although each differs in magnitude. The parameter fmin is a measure of the Dregion ionization (Chandra et al, 1997). During the eclipse day fmin values dropped below 1.5 MHz, corresponding to a decrease of about 62% in respect to the normal daytime values.…”