• ABHA SINGH

      Articles written in Journal of Astrophysics and Astronomy

    • Causes responsible for intense and severe storms during the declining phase of Solar Cycle 24

      KALPANA PATEL ABHA SINGH S. B. SINGH A. K. SINGH

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      The occurrence of total 113 geomagnetic storms during declining phase of Solar Cycle 24 (2015–2017) subdivided as about 105 moderate storms (${\rm Dst} = −50$ nT to $−$100 nT), 6 intense storms (${\rm Dst} = −100$ nTto $−$200 nT) and 2 severe storms (Dst < $−$200 nT) has been diagnosed on the basis of 5 day active window through the CACTus (Computer aided CME tracking) software. A detailed study has been carried out for the 6intense and 2 severe storms. It is inferred that CMEs are the major source of geomagnetic storms to occur. Out of the 6 intense and 2 severe storms, only 1 has been observed with the origin of CIR. Thus, all analyzed intensegeomagnetic storms are due to coronal mass ejection at the Sun. Most of our results are in good accordance with other reported results.

    • Effect of intense solar flares on TEC variation at low-latitude station Varanasi

      ABHA SINGH S. S. RAO V. S. RATHORE SUDESH K. SINGH A. K. SINGH

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      The effect of intense solar flares on total electron content (TEC) variability during the declining phase of solar cycle-24 is studied at the low-latitude station at Varanasi, India (Geog. Lat. 25.31$^{\circ}$ N, Geog. Long. 82.97$^{\circ}$ E, Geomag. Lat. 16.54$^{\circ}$ N, Geomag. Long. 157.09$^{\circ}$ E). In the present paper, we have chosen the intense solar flares that occurred during 9–13 March 2015, 1–2 January 2016, 12–14 February 2016, 6–8 August 2016, and 6–8 September 2017 in the solar cycle-24 period for which the data is available. Our results showed significant enhancements in TEC up to the order of 15 TECU during and after the solar flare events. We have also given a brief account of solar flare effect in TEC with and without geomagnetic disturbances, local time effects (solar zenith angle effects) and changing the location of the solar active region. In a few cases, our results revealed a delay in TEC response during the flare peak time as well as recovery time.

    • Effect of intense geomagnetic storms on low-latitude TEC during the ascending phase of the solar cycle 24

      ABHA SINGH VISHNU S. RATHORE SANJAY KUMAR S. S. RAO SUDESH K. SINGH A. K. SINGH

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      The results presented in this paper are obtained from low-latitude ionospheric total electron content (TEC) variation during the chosen geomagnetic storm events happening during the solar cycle 24.We include the four intense geomagnetic storms that occurred on 26 September 2011, 15 July 2012, 19 February 2014 and 20 December 2015, depending upon the availability of TEC data. For this, we have used the TEC data from low-latitude station Varanasi (geographic latitude 25$^{\circ}$, 16$'$N, geographic longitude 82$^{\circ}$, 59$'$E and geomagnetic latitude 16$^{\circ}$, 24$'$N) and an equatorial station Bengaluru (geographic latitude 13$^{\circ}$, 02$'$N, geographic longitude 77$^{\circ}$, 34$'$E and geomagnetic latitude 04$^{\circ}$, 68$'$N). The storm-induced TEC changes at chosen stations have been discussed in terms of local time, storm wind effect, neutral wind, composition changes and variation in the dawn–dusk component of the interplanetary electric field (IEF $E_y$).

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      Posted on January 27, 2016

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