Scholarly Publications
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This community showcases the academic contributions of faculty and researchers at Banaras Hindu University (BHU) and provides a year-wise compilation of publications across disciplines. Institutional Repository BHU
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PublicationArticle Observed (GPS) and modeled (IRI and TIE-GCM) TEC trends over southern low latitude during solar cycle-24(Elsevier Ltd, 2023) S.S. Rao; Monti Chakraborty; A.K. SinghThe Total Electron Content (TEC) derived from the Global Positioning System (GPS) measurements during the solar cycle-24 at COCO Island (12.20⁰ S, 96.80⁰ E) are compared with those of International Reference Ionosphere-2016 (IRI-2016) model and Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM). TEC data derived from the above two models follow the nature of observed variations with considerable divergences in amplitudes. The precision of model TEC in reference to GPS TEC is discussed using a correlation coefficient, mean difference, root mean square error, and relative deviation module mean techniques. The randomness of predictions is found to be biased by the solar cycle, season, and local time. The simulated values showed better accuracy during the low solar activity and night hours. This study is an extension of Rao et al. (2019b), in which we reported similar study of TEC variability at the northern low latitude station. First of all, it is observed from two studies that the magnitude of TEC is greater at the southern low latitude than at the northern low latitude. Also the correlation between GPS TEC/ IRI TEC and F10.7 flux is determined to be greater at northern low latitude station compared to southern low latitude station. However, TIE-GCM TEC values are found to be slightly more correlated with F10.7 flux at southern low latitude station compared to northern low latitude station. With regard to seasonal variation, semiannual oscillations in TEC are found to be coherent on both sides of the equator. However, the winter anomaly is not observed or predicted by models at the southern low latitude whereas it is observed to be a solar flux-dependent feature at the northern low latitude. The IRI model closely follows seasonal trends of TEC whereas TIE-GCM over-predicted TEC during solstices at the northern low latitudes. Models TEC deviations are found to be lesser at the southern low latitude compared to northern low latitude. © 2022 COSPARPublicationBook Chapter Study of the atmospheric and ionospheric phenomenon using GPS-based remote sensing technique(Elsevier, 2022) Sanjay Kumar; S.S. Rao; Mukulika Mondal; A.K. SinghAtmosphere including the ionosphere acting as a threat to global positioning system (GPS) signals which can provide valuable information about content of the medium. Ionospheric and tropospheric delay measurements using dual frequency GPS computations made at L1 and L2 frequencies enable reliable estimation of the gradually varying ionospheric and atmospheric conditions and hence estimation of total electron content and water vapor, respectively. Our atmosphere and ionosphere are very much sensitive to several natural and hazardous events, such as earthquakes, thunderstorms, space weather, solar eclipse, cyclone, typhoon, sudden stratospheric warming, etc. In this chapter, influences, tracking, forecasting of hazardous events such as earthquakes, thunderstorms, solar eclipse, cyclone, typhoon, sudden stratospheric warming using data from ground-based GPS measurements will be discussed. Besides, the significance of water vapor as a greenhouse gas and global warming, weather phenomenon, and climate variation and its relevance in modern society will be also been discussed. Finally, scope and challenges of the above phenomenon using GPS-based measurements are discussed. © 2023 Elsevier Ltd. All rights reserved.PublicationBook Chapter Probing the upper atmosphere using GPS(Elsevier, 2021) S.S. Rao; A.K. SinghThe Global Positioning System satellites provide an extensive array of beacon signals at L-band frequencies (1.2 and 1.6GHz), which are used for satellite-based navigation, communication, and ground positioning. Before being received at the ground, these signals have to pass through the ionosphere. The ionosphere is a dispersive medium, whose variability affects the quality of the received signal, and is a matter of grave concern for civilian as well as military applications that rely on these signals. The ionospheric plasma density drastically changes during various solar (solar flare, corona mass ejection), astronomical (solar eclipse), and seismological (earthquake) phenomena. Understanding these processes is of great scientific value and has practical benefits in satellite-based communication and navigation. In this chapter, a brief overview on ionospheric weather and outcomes of studies on solar, astronomical, and terrestrial phenomena employed worldwide is discussed. © 2021 Elsevier Inc. All rights reserved.PublicationBook Chapter Probing the tropospheric water vapor using GPS(Elsevier, 2021) Sanjay Kumar; R.P. Singh; A.K. SinghThis chapter provides a brief introduction about Global Positioning System (GPS), its structures, and working principle with applications mainly to water vapor measurements. A brief introduction about signals transmitted from GPS satellites, signal structures, and their propagations from satellite to receiver has also been presented. During the signal propagation from satellite to receiver, several errors such as satellite clock error, ephemeris error, atmospheric error, multipath error, receiver noises are introduced in the signals, which have also been discussed. Atmosphere acts as a threat for Global Navigation Satellite System signal and provides valuable information about content of the medium. The presence of water vapor in addition to dry components such as oxygen and nitrogen degrades the GPS signal significantly, and its estimation gives information about water vapor content of the atmosphere. Usually, water vapor resides in the troposphere, and hence tropospheric error measurement in GPS signal is used to determine water vapor contents. Water vapor is an important component of global warming, weather phenomenon, numerical weather prediction (NWP), hydrological cycle, and climate variation, and hence its precise estimation is most relevant in modern society. For NWP point of view, tomographic modeling of water vapor with relevant accuracy is a challenging task. Finally, scope and challenges of water vapor measurement are discussed. © 2021 Elsevier Inc. All rights reserved.PublicationArticle Ionospheric and atmospheric perturbations due to two major earthquakes (M >7.0)(Springer, 2021) Sanjay Kumar; Prashant Kumar Singh; Rohtash Kumar; A.K. Singh; R.P. SinghThe perturbation produced in the atmosphere/ionosphere associated with earthquake precursors during seismic activity of two major earthquakes which occurred on (1) 24 June 2019 in Indonesia (M = 7.3) and (2) on 19 August 2018 at Ndoi, Fiji (M = 8.2), are studied. Based on statistical analysis of total electron content (TEC) data, the presence of ionospheric perturbations 5 days before and after the main shock are found, which depends on the distance as well as direction of observation point from the epicentre. In general, ionospheric perturbations after the EQ at all the stations are found larger than that before the EQ. Probable mechanisms behind these perturbations associated with EQ are also being discussed. The ionospheric perturbations are observed at stations which are at larger distances from the epicentre, but not observed over other stations in different directions which are comparatively closer to the epicentre. These results suggest that seismic induced ionospheric anomaly is not isotropic in nature. Ozone data from three satellites: AIRS, OMI, and TOMS-like and MERRA-2 model are also analyzed 5 days before the EQ day and compared to the monthly average level. A strong link between anomalous variation in ionospheric TEC and atmospheric ozone data prior to both the EQs is noticed. © 2021, Indian Academy of Sciences.PublicationArticle Seismogenic ionospheric anomalies associated with the strong Indonesian earthquake occurred on 11 April 2012 (M = 8.5)(Elsevier Ltd, 2018) Uma Pandey; Ashutosh K. Singh; Sanjay Kumar; A.K. SinghIonospheric perturbations in possible association with a major earthquake (EQ) (M = 8.5) which occurred in India-Oceania region are investigated by monitoring subionospheric propagation of VLF signals transmitted from the NWC transmitter (F = 19.8 kHz), Australia to a receiving station at Varanasi (geographic lat. 25.3°N, long 82.99°E), India. The EQ occurred on 11 April 2012 at 08:38:35 h UT (magnitude ≈ 8.5, depth = 10 km, and lat. = 2.3°N, long. = 93.0°E). A significant increase of few days before the EQ has been observed by using the VLF nighttime amplitude fluctuation method (fixed frequency transmitter signal). The analysis of total electron contents (TEC) derived from the global positioning system (GPS) at three different stations namely, Hyderabad (latitude 17.38°N, longitude 78.48°E), Singapore (latitude 1.37°N, longitude 103.84°E) and Port Blair (latitude 11.62°N, longitude 92.72°E) due to this EQ has also been presented. Significant perturbation in TEC data (enhancements and depletion) is noted before and after the main shock of the EQ. The possible mechanisms behind these perturbations due to EQ have also been discussed. © 2017 COSPARPublicationArticle Changes in total electron content (TEC) during the annular solar eclipse of 15 January 2010(Elsevier Ltd, 2012) Sanjay Kumar; A.K. SinghThe solar eclipse of 15 January 2010 was an annular eclipse of the Sun with a maximum magnitude of 0.96 at 1.62°N, 69.29°E. To study the effect of this solar eclipse on the ionosphere the GPS data recorded at three different Indian stations Varanasi (Geographic latitude 25°, 16′N, longitude 82°, 59′E), Hyderabad (Geographic latitude 17°, 20′N, longitude 78°, 30′E) and Bengaluru (Geographic latitude 12°, 58′N, longitude 77°, 33′E) have been used to retrieve ionospheric total electron content (TEC). The ionospheric response to this rare event has been studied in terms of GPS-derived TEC observed at all the three Indian stations. A significant reduction in TEC reflected by all PRNs at all the three stations has been observed. The magnitude of the reduction in VTEC compared to quiet mean VTEC depends on latitude as well as longitude. The amount of reduction observed from different satellites (PRN) is different and depends on the location of the satellite from the solar eclipse path. © 2011 COSPAR. Published by Elsevier Ltd. All rights reserved.PublicationArticle GPS-TEC variations during low solar activity period (2007-2009) at Indian low latitude stations(2012) Sanjay Kumar; S. Priyadarshi; Gopi Krishna; A.K. SinghThe paper is based on the ionospheric variations in terms of vertical total electron content (VTEC) for the low solar activity period from May 2007 to April 2009 based on the analysis of dual frequency signals from the Global Positioning System (GPS) satellites recorded at ground stations Varanasi (Geographic latitude 25°16′ N, Longitude 82°59′ E), situated near the equatorial ionization anomaly crest and other two International GNSS Service (IGS) stations Hyderabad (Geographic latitude 17°20′ N, longitude 78°30′ E) and Bangalore (Geographic latitude 12°58′ N, longitude 77°33′ E) in India. We describe the diurnal and seasonal variations of total electron content (TEC), and the effects of a space weather related event i. e. a geomagnetic storm on TEC. The mean diurnal variation during different seasons is brought out. It is found that TEC at all the three stations is maximum during equinoctial months (March, April, September and October), and minimum during the winter months (November, December, January and February), while obtaining intermediate values during summer months (May, June, July and August). TEC shows a semi-annual variation. TEC variation during geomagnetic quiet as well as disturbed days of each month and hence for each season from May 2007 to April 2008 at Varanasi is examined and is found to be more during disturbed period compared to that in the quiet period. Monthly, seasonal and annual variability of GPS-TEC has been compared with those derived from International Reference Ionosphere (IRI)-2007 with three different options of topside electron density, NeQuick, IRI01-corr and IRI 2001. A good agreement is found between the GPS-TEC and IRI model TEC at all the three stations. © 2012 Springer Science+Business Media B.V.PublicationArticle GPS derived ionospheric TEC response to geomagnetic storm on 24 August 2005 at Indian low latitude stations(Elsevier Ltd, 2011) Sanjay Kumar; A.K. SinghResults pertaining to the response of the low latitude ionosphere to a major geomagnetic storm that occurred on 24 August 2005 are presented. The dual frequency GPS data have been analyzed to retrieve vertical total electron content at two Indian low latitude stations (IGS stations) Hyderabad (Geographic latitude 17°20′N, Geographic longitude 78°30′E, Geomagnetic latitude 8.65°N) and Bangalore (Geographic latitude 12°58′N, Geographic longitude 77°33′E, Geomagnetic latitude 4.58°N). These results show variation of GPS derived total electron content (TEC) due to geomagnetic storm effect, local low latitude electrodynamics response to penetration of high latitude convection electric field and effect of modified fountain effect on GPS-TEC in low latitude zone. © 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.