Navegando por Autor "Venkatesh, Karnam"

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    Daily and Monthly Variations of the Equatorial Ionization Anomaly (EIA) Over the Brazilian Sector During the Descending Phase of the Solar Cycle 24
    (Advancing Earth and Space Sciences) Dias, Maukers Alem Lima; Fagundes, Paulo Roberto; Venkatesh, Karnam; Pillat, Valdir Gil; Ribeiro, Brunno Augusto Gomes; Seemala, Gopi K.; Arcanjo, Mateus de Oliveira
    It has been noticed recently that the equatorial ionization anomaly (EIA) in the Brazilian eastern, middle, and western sectors present significant longitudinal variability within a short separation due to the presence of typical magnetic field structure over South America. Therefore, the main motivation of this study is to investigate day‐to‐day and month‐to‐month characteristics of the EIA in three closely spaced longitudinal sectors over the Brazilian region during the year 2016 in the descending phase of the solar activity. These three longitudinal sectors are perpendicular to the magnetic equator at its largest declination over the globe. The EIA showed a semiannual variation in all sectors with a major maximum during the summer, a minimum during the winter, and secondary maximum during spring. In addition, the EIA shows its classical behavior with a trough around the magnetic equator and crests at low latitudes (from ±15° to ±20°). When the EIA is not developed, the maximum ionization is located around the dip equatorial latitudes and the anomaly crest is absent. The number of days within 1 year that showed clear EIA development in the west, middle, and east sectors is 248 (78.2%), 236 (74.4%), and 265 (83.6%), respectively. The undeveloped/absence of EIA is also found often during the months of winter, and the numbers of such days during 2016 in the west, middle, and east are 69 (21.8%), 81 (25.6%), and 52 (16.4%), respectively. Also, the shape, strength, extent, and lifetimes of EIA crest have shown significant variabilities between the three sectors during different seasons. Further, a comparative analysis is carried out on the variations of EIA crest and lifetime between GPS observations and IRI‐2016 model, and the results are discussed.
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    Ionospheric disturbances in a large area of the terrestrial globe by two strong solar flares of September 6, 2017, the strongest space weather events in the last decade
    (Elsevier) Fagundes, Paulo Roberto; Pezzopane, Michael; Habarulema, John Bosco; Venkatesh, Karnam; Dias, Maukers Alem Lima; Tardelli, Alexandre; Abreu, Alessandro José de; Pillat, Valdir Gil; Pignalberi, Alessio; Bolzan, Maurício José Alves; Ribeiro, Brunno Augusto Gomes; Vieira, Francisco; Raulin, Jean-Pierre; Denardini, Clezio Marcos; Seemala, Gopi K.; Arcanjo, Mateus de Oliveira
    On September 6, 2017, the solar active region AR 2673 emitted two solar flares: the first at 08:57 UT (X2.2) and the second at 11:53 UT (X9.3); both were powerful enough to black-out high and low frequency radio waves (where UT is universal time). The X9.3 was the strongest solar flare event in the past decade. In this study, we took the advantage of these two extreme flare events to investigate cor- responding effects on the ionosphere using multi-instrument observations from magnetometers, Global Positioning System – Total Elec- tron content (GPS-TEC) receivers, ionosondes and Swarm satellites over a large geographical extent covering South American, African and European sectors. During the X2.2 flare, European and African sectors were sunlit and during X9.3 European, African, and South American sectors were sunlit and exposed to the solar flare radiation. During the X2.2 flare, there was an ionosonde blackout for a dura- tion of about 45 min, while during the X9.3 flare this blackout lasted for 1 h and 30 min. The blackout are seen over a large global extent which demonstrates the severity of solar flare events in disrupting the radio communication. The horizontal component of Earth’s geo- magnetic field has shown ripples and enhancements during these flare events. The ionospheric Vertical Total Electron Content (VTEC) showed a positive phase along with an intensification of the Equatorial Ionization Anomaly (EIA) over the South American and African sectors. The dynamical and physical processes associated with the TEC and EIA variabilities due to solar flare are discussed.