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Extreme space weather events of solar cycle 24: X-class solar flares and their impact on the low-latitude D-region ionosphere


Affiliations
1 KSK Geomagnetic Research Laboratory, Indian Institute of Geomagnetism, Prayagraj 211 506, India., India
2 Department of Physics, Babasaheb Bhimrao Ambedkar University, Lucknow 226 025, India., India
3 K. Banerjee Centre of Atmospheric and Ocean Studies, University of Allahabad, Prayagraj 221 002, India., India
 

X-class solar flares, which occurred in the daytime from 2008 to 2016 during solar cycle 24, were studied for their influence on the lower ionosphere over the low-equatorial Indian region. To understand the D-region behaviour during flare events, we used the very low frequency (VLF) navigational transmitter NWC (19.8 kHz) signal recorded at Pryagraj, Uttar Pradesh, India. A total of seven parameters were estimated: (i) the magnitude of X-ray flux, (ii) VLF signal rising amplitude perturbation (SRAP), (iii) X-ray flux and NWC signal start time difference (STD), (iv) peak time difference (PTD), (v) Wait’s ionospheric parameters h′ (reference height), (vi) β (sharpness factor) and (vii) D-region electron density difference (EDD) to determine the overall effect of solar flares on the D-region. The results suggest that three parameters (X-ray flux, SRAP and h′) show a decreasing trend through the linear fit line, two parameters (β and EDD) show an increasing trend, while the remaining two parameters show a mixed trend (decrease during low activity and increase during high activity). Further, the trend line during the diurnal variation shows an increasing trend for X-ray flux, PTD and h′, and a decreasing trend for SRAP, STD, β and EDD. Deviation in the case of individual events may indicate the dependence of these parameters on the seasons as well. The present study will provide the base for more robust analysis and modelling work in the future to understand the complexity of ionospheric change during flare events, and to develop a predictive model for space weather mitigation.

Keywords

D-Region Ionosphere, Space Weather, Solar Cycle, Solar Flares, Trend Line, Vlf Waves.
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  • Extreme space weather events of solar cycle 24: X-class solar flares and their impact on the low-latitude D-region ionosphere

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Authors

K. Venkatesham
KSK Geomagnetic Research Laboratory, Indian Institute of Geomagnetism, Prayagraj 211 506, India., India
Ajeet K. Maurya
Department of Physics, Babasaheb Bhimrao Ambedkar University, Lucknow 226 025, India., India
Rajesh Singh
KSK Geomagnetic Research Laboratory, Indian Institute of Geomagnetism, Prayagraj 211 506, India., India
Suneet Dwivedi
K. Banerjee Centre of Atmospheric and Ocean Studies, University of Allahabad, Prayagraj 221 002, India., India

Abstract


X-class solar flares, which occurred in the daytime from 2008 to 2016 during solar cycle 24, were studied for their influence on the lower ionosphere over the low-equatorial Indian region. To understand the D-region behaviour during flare events, we used the very low frequency (VLF) navigational transmitter NWC (19.8 kHz) signal recorded at Pryagraj, Uttar Pradesh, India. A total of seven parameters were estimated: (i) the magnitude of X-ray flux, (ii) VLF signal rising amplitude perturbation (SRAP), (iii) X-ray flux and NWC signal start time difference (STD), (iv) peak time difference (PTD), (v) Wait’s ionospheric parameters h′ (reference height), (vi) β (sharpness factor) and (vii) D-region electron density difference (EDD) to determine the overall effect of solar flares on the D-region. The results suggest that three parameters (X-ray flux, SRAP and h′) show a decreasing trend through the linear fit line, two parameters (β and EDD) show an increasing trend, while the remaining two parameters show a mixed trend (decrease during low activity and increase during high activity). Further, the trend line during the diurnal variation shows an increasing trend for X-ray flux, PTD and h′, and a decreasing trend for SRAP, STD, β and EDD. Deviation in the case of individual events may indicate the dependence of these parameters on the seasons as well. The present study will provide the base for more robust analysis and modelling work in the future to understand the complexity of ionospheric change during flare events, and to develop a predictive model for space weather mitigation.

Keywords


D-Region Ionosphere, Space Weather, Solar Cycle, Solar Flares, Trend Line, Vlf Waves.

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DOI: https://doi.org/10.18520/cs%2Fv124%2Fi7%2F812-819