Ionospheric effects near the magnetic equator and the anomaly crest of the Indian longitude zone during a large number of intense geomagnetic storms |
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| Authors: | R Hajra SK Chakraborty A DasGupta |
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| Institution: | 1. Department of Physics, Raja Peary Mohan College, Uttarpara, Hooghly 712258, India;2. S. K. Mitra Center for Research in Space Environment, University of Calcutta, Calcutta 700009, India;1. NASI Sr. Scientist, Physical Research Laboratory, Ahmedabad 380009, India;2. NASI RA, Physical Research Laboratory, Ahmedabad 380009, India;3. Indian Institute of Geomagnetism, Navi Mumbai 410218, India;4. On deputation from Airports Authority of India, Space Application Centre, Ahmedabad 380015, India;5. Space Physics Laboratory, VSSC, Trivandrum 695022, India;1. Mbarara University of Science and Technology, Mbarara, Uganda;2. South African National Space Agency (SANSA) Space Science, 7200 Hermanus, South Africa;3. Department of Physics and Electronics, Rhodes University, 6140 Grahamstown, South Africa;1. S.K. Mitra Center for Research in Space Environment, University of Calcutta, 92, A.P.C. Road, Calcutta 700009, India;2. Institute of Radio Physics and Electronics, University of Calcutta, 92, A.P.C. Road, Calcutta 700009, India;1. Department of Physics, Catholic University of America, Washington, DC 20064, USA;2. NASA Goddard Space Flight Center, Code 674, Greenbelt, MD 20771, USA;3. Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan;4. South African National Space Agency (SANSA) Space Science, Hermanus 7200, South Africa |
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| Abstract: | Ionospheric effects of a large number (51) of severe geomagnetic storms are studied using total electron content (TEC) and VHF/UHF scintillation data from Calcutta, situated near the northern crest of equatorial ionization anomaly and equatorial spread-F (ESF) data from Kodaikanal. The susceptibility of the equatorial ionosphere to develop storm time plasma density irregularities responsible for ESF and scintillation is found to be largely modulated by the local times of occurrences of main and recovery phases as seen in the Dst index. While inhibition of premidnight scintillation for lower TEC values compared to the quiet day averages is omnipresent, occurrence of scintillation for enhancements of TEC is largely dependent on initiation time and amplitude of the said deviations. An overall reduction in threshold values of h′F for observing storm induced ESF and scintillation compared to reported quiet time values is noted. The results are discussed in terms of storm time variabilities in electric fields, neutral wind system and composition changes. |
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