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Author

Shubham Sarkar

Bio: Shubham Sarkar is an academic researcher from University of Calcutta. The author has contributed to research in topics: Ionosphere & Very low frequency. The author has an hindex of 2, co-authored 3 publications receiving 6 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, the D-region ionospheric disturbances due to the tropical cyclone Fani over the Indian Ocean have been analyzed using Very Low Frequency (VLF) radio communication signals from three transmitters (VTX, NWC and JJI) received at two low latitude stations (Kolkata-CUB and Cooch Behar-CHB).

7 citations

Proceedings ArticleDOI
01 Aug 2020
TL;DR: In this paper, very low frequency radio signals received from two places Kolkata and Cooch Behar, India revealed disturbances in the lower ionosphere namely in the D-region ionosphere.
Abstract: We present new observations of lower ionospheric disturbances due to the extremely severe cyclonic storm ‘Fani’ over northeastern part of the Indian Ocean. Very Low Frequency radio signals received from two places Kolkata and Cooch Behar, India revealed disturbances in the lower ionosphere namely in the D-region ionosphere. Mesospheric temperature and Ozone concentration data from the NASA’s TIMED satellite were also used to diagnose the disturbances in the lower ionosphere. Significant wavelike oscillations and strong amplitude anomalies in daytime and nighttime VLF signal were observed during the intense phase of the cyclone. Both the mesospheric Ozone concentration and temperature showed maximum anomalies beyond $3 \sigma$ during the cyclone period. Mesospheric temperature enhancement around VLF reflection heights indicates changes in the chemical composition and electron-neutral balance in the D-region ionosphere. Wavelet analysis of the VLF amplitudes indicates a strong anti-correlation of the total wavelet power in the wave-band of periods 10-30 min with the cyclone pressure which suggests a possibility of monitoring cyclone intensity from mesospheric gravity waves using VLF radio measurements.

Cited by
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Journal ArticleDOI
TL;DR: In this article, the D-region ionospheric disturbances due to the tropical cyclone Fani over the Indian Ocean have been analyzed using Very Low Frequency (VLF) radio communication signals from three transmitters (VTX, NWC and JJI) received at two low latitude stations (Kolkata-CUB and Cooch Behar-CHB).

7 citations

Journal ArticleDOI
TL;DR: In this paper , the authors analyzed the JJI VLF (22.2 kHz) transmitter signal received at two low-latitude stations, one in Port Vila (geogrga coord., 17.73°S, 168.33°E), Vanuatu and other in Suva (18.14°S and 178.44°E, Fiji, was analyzed for any VlF changes due to 16 Earthquakes (EQs) with magnitudes 5.5 to 7.7, during 2018 (JJI-Vanuatu path, 6.8 Mm) and 2007 to 2018 ( JJI-Suva path, 7.5 Mm).

3 citations

DOI
01 Aug 2022
TL;DR: In this paper , the effects of three solar eclipses (January 2019, December 2019, and June 2020) observed by very low frequency (VLF) radio signals from a single receiver at a subtropical low-latitude station in India is presented.
Abstract: Ionospheric impact of three solar eclipses (January 2019, December 2019, and June 2020) observed by Very Low Frequency (VLF) radio signals from a single receiver at a subtropical low‐latitude station in India is presented here. Perturbations in signal amplitudes of VLF transmitters such as the VTX (18.2 kHz), NWC (19.8 kHz), JJI (22.2 kHz), and DHO (23.4 kHz) are analyzed. Both positive, negative, and also mixed‐type of amplitude deviations are observed which are explained based on the solar eclipse obscuration profiles over the entire propagation paths. The difference in observed amplitude deviations for a VLF signal during the different solar eclipses are reproduced using the Long Wave Propagation Capability code and solar obscuration profile. Particularly, the effects of two solar eclipses on the VLF signal propagation characteristics have been analyzed. The modal attenuation coefficients of the VTX signal in the earth‐ionosphere waveguide are decreased with the increase of solar obscuration. A negative linear relationship of VLF signal attenuation with solar obscuration has been found for the first time during the solar eclipse. The relations are almost similar for the two solar eclipses of December 2019 and June 2020. Further, the percentage reduction of the D‐region electron density profiles as a function of altitude and solar obscuration during the two solar eclipses is presented.

1 citations

Proceedings ArticleDOI
01 Aug 2020
TL;DR: In this paper, very low frequency radio signals received from two places Kolkata and Cooch Behar, India revealed disturbances in the lower ionosphere namely in the D-region ionosphere.
Abstract: We present new observations of lower ionospheric disturbances due to the extremely severe cyclonic storm ‘Fani’ over northeastern part of the Indian Ocean. Very Low Frequency radio signals received from two places Kolkata and Cooch Behar, India revealed disturbances in the lower ionosphere namely in the D-region ionosphere. Mesospheric temperature and Ozone concentration data from the NASA’s TIMED satellite were also used to diagnose the disturbances in the lower ionosphere. Significant wavelike oscillations and strong amplitude anomalies in daytime and nighttime VLF signal were observed during the intense phase of the cyclone. Both the mesospheric Ozone concentration and temperature showed maximum anomalies beyond $3 \sigma$ during the cyclone period. Mesospheric temperature enhancement around VLF reflection heights indicates changes in the chemical composition and electron-neutral balance in the D-region ionosphere. Wavelet analysis of the VLF amplitudes indicates a strong anti-correlation of the total wavelet power in the wave-band of periods 10-30 min with the cyclone pressure which suggests a possibility of monitoring cyclone intensity from mesospheric gravity waves using VLF radio measurements.
Journal ArticleDOI
TL;DR: In this article , Doppler measurements at oblique propagation paths from the city of Harbin, the People's Republic of China (PRC), to 10 high-frequency (HF) radio broadcast stations in the PRC, Japan, Mongolia, and the Republic of Korea captured the response in the ionosphere to the activity of the super typhoon, Typhoon Kong-rey, from 30 September to 6 October 2018.
Abstract: Abstract. Doppler measurements at oblique propagation paths from the city of Harbin, the People's Republic of China (PRC), to 10 high-frequency (HF) radio broadcast stations in the PRC, Japan, Mongolia, and the Republic of Korea captured the response in the ionosphere to the activity of the super typhoon, Typhoon Kong-rey, from 30 September to 6 October 2018. The Harbin Engineering University coherent software-defined radio system generates the database containing the complex amplitudes of the radio signals that have been acquired along 14 propagation paths since 2018. The complex amplitudes are used for calculating the temporal dependences of the Doppler spectra and signal amplitudes, and the Doppler spectra are used to plot the Doppler shift as a function of time, fD(t), for all rays. The scientific objectives of this study are to reveal the possible perturbations caused by the activity of Typhoon Kong-rey and to estimate the magnitudes of wave parameters of the ionospheric plasma and radio signals. The amplitudes, fDa, of the Doppler shift variations were observed to noticeably increase (factor of ∼2–3) on 1–2 and 5–6 October 2018, while the 20–120 min periods, T, of the Doppler shift variations suggest that the wavelike disturbances in the ionosphere are caused by atmospheric gravity waves. The periods and amplitudes of quasi-sinusoidal variations in the Doppler shift, which have been determined for all propagation paths, may be used to estimate the amplitudes, δNa, of quasi-sinusoidal variations in the electron density. Thus, T≈20 min and fDa≈0.1 Hz yield δNa≈0.4 %, whereas T≈30 min and fDa≈0.2 Hz give δNa≈1.2 %. If T≈60 min and fDa≈0.5 Hz, then δNa≈6 %. The periods T are found to change within the 15–120 min limits, and the Doppler shift amplitudes, fDa, show variability within the 0.05–0.4 Hz limits.