Browsing by Author "Venkatesh, K."
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Item Restricted Effects of the intense geomagnetic storm of September–October 2012 on the equatorial, low- and mid-latitude F region in the American and African sector during the unusual 24th solar cycle(Elsevier, 2015-12-30) Jesus, R. de; Fagundes, P. R.; Coster, A.; Bolaji, O. S.; Sobral, J. H. A.; Batista, I. S.; Abreu, A. J. de; Venkatesh, K.; Gende, M.; Abalde, J. R.; Sumod, S. G.The main purpose of this paper is to investigate the response of the ionospheric F layer in the American and African sectors during the intense geomagnetic storm which occurred on 30 September–01 October 2012. In this work, we used observations from a chain of 20 GPS stations in the equatorial, low- and mid-latitude regions in the American and African sectors. Also, in this study ionospheric sounding data obtained during 29th September to 2nd October, 2012 at Jicamarca (JIC), Peru, São Luis (SL), Fortaleza (FZ), Brazil, and Port Stanley (PST), are presented. On the night of 30 September–01 October, in the main and recovery phase, the h´F variations showed an unusual uplifting of the F region at equatorial (JIC, SL and FZ) and mid- (PST) latitude stations related with the propagations of traveling ionospheric disturbances (TIDs) generated by Joule heating at auroral regions. On 30 September, the VTEC variations and foF2 observations at mid-latitude stations (American sector) showed a long-duration positive ionospheric storm (over 6 h of enhancement) associated with large-scale wind circulations and equatorward neutral winds. Also, on 01 October, a long-duration positive ionospheric storm was observed at equatorial, low- and mid- latitude stations in the African sector, related with the large-scale wind circulations and equatorward neutral winds. On 01 and 02 October, positive ionospheric storms were observed at equatorial, low- and mid-latitude stations in the American sector, possibly associated with the TIDs and an equatorward neutral wind. Also, on 01 October negative ionospheric storms were observed at equatorial, low- and mid-latitude regions in the American sector, probably associated with the changes in the O/N2 ratio. On the night of 30 September–01 October, ionospheric plasma bubbles were observed at equatorial, low- and mid- latitude stations in the South American sector, possibly associated with the occurrence of geomagnetic storm.Item Restricted The role of altitudinal variation of scale height in determining the topside electron density profile over equatorial and low latitude sectors(Elsevier, 2014-10-23) Venkatesh, K.; Rama Rao, P. V. S.; Fagundes, Paulo R.Studies on the topside electron density profile variations have gained significant importance in the recent past in view of the trans-ionospheric communication and navigation applications particularly over the equatorial and low latitude sectors. The determination of scale height to be used in analytical functions has become more important in estimating the vertical electron density profile in the topside ionosphere. The incoherent scatter radar data over an equatorial station Jicamarca and a low latitude station Arecibo during the high solar activity years 2001 and 2002 are used to estimate the altitudinal dependence of topside ionospheric scale height. These scale height values at different altitudes are used to reconstruct the topside electron density profiles to study the changes in the shape of the topside profile due to the varying scale height values. It has been observed that a closer estimates of the electron density profiles in the topside ionosphere can be derived by using scale height values around 550 km over Jicamarca and around 500 km over Arecibo. The IRI-2012 modeled electron density profiles have been derived by giving F-layer peak density and height as inputs and those modeled profiles are compared with ISR measured and reconstructed profiles. Further, the scale height values in the topside ionosphere are computed using the IRI-2012 modeled electron and ion temperatures around 550 km altitudes over Jicamarca and around 500 km altitude over Arecibo. The scale height values thus derived have been used to reconstruct the topside electron density profiles over Jicamarca and Arecibo, the results of which have also been discussed in this paper.