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Suman Ray

Bio: Suman Ray is an academic researcher from Indian Centre for Space Physics. The author has contributed to research in topics: Very low frequency & Solar eclipse. The author has an hindex of 9, co-authored 21 publications receiving 236 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the amplitude of the nighttime VLF signals anomalously fluctuated 4 days before the Indian Navy station VTX received an earthquake of magnitude 7.4 at Southwestern Pakistan (latitude 28.9°N, longitude 64°E).
Abstract: We have presented the result of the analysis of the nighttime VLF signals transmitted from the Indian Navy station VTX (latitude 8.43°N, longitude 77.73°E) at 19.2 kHz and received at Kolkata (latitude 22.57°N, longitude 88.24°E). On 18th January, 2011 an earthquake of magnitude 7.4 occurred at Southwestern Pakistan (latitude 28.9°N, longitude 64°E). We have analyzed the nighttime VLF signals for 2 weeks around 18th of January, 2011 to see if there have been any precursory effects of this earthquake. We have found that the amplitude of the nighttime VLF signals anomalously fluctuated 4 days before the earthquake. This agrees well with our previous findings based on the analysis of 1 year of earthquake data.

48 citations

Journal ArticleDOI
TL;DR: In this article, the amplitude variation of the diurnal signal at each of these receiving stations in winter and summer was compared and the results generally agree with the signal shapes obtained using the long wave propagation capability code based on mode propagation through the Earth-ionosphere cavity.
Abstract: We have carried out 2 week-long campaigns in Indian winter and summer to study VLF signals from the Indian navy transmitter (VTX) operating at 18.2 kHz. We have used more than a dozen of receivers scattered throughout the Indian sub-continent in each of these campaigns. To our knowledge, this is the largest campaign of its kind in this region. The propagation paths range from 500 km to almost 3,000 km covering an area of about 4 million sq km. We have presented the results of the amplitude variation of the diurnal signal at each of these receiving stations in winter and summer and compare them. We have clearly found the non-reciprocity of the east to west and west to east propagation. Our results generally agree with the signal shapes obtained using the long wave propagation capability code based on mode propagation through the Earth-ionosphere cavity.

45 citations

Journal ArticleDOI
TL;DR: In this article, the authors present the results of an analysis of night time data of the VLF signal amplitude from the Indian Navy station VTX at 182 kHz, received by the Indian Centre for Space Physics, Kolkata.
Abstract: We present the results of an analysis of year-long (2007) monitoring of night time data of the VLF signal amplitude from the Indian Navy station VTX at 182 kHz, received by the Indian Centre for Space Physics, Kolkata We analyzed this data to find out the correlation, if any, between night time amplitude fluctuation and seismic events We found, analyzing individual cases (with magnitudes >5) as well as statistical analysis (of all the events with effective magnitudes greater than 35), that night time fluctuation of the signal amplitude has the highest probability to be beyond the 2σ level about three days prior to seismic events Thus, the night time fluctuation could be considered as a precursor to enhanced seismic activities

44 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present the results of their campaign and give an interpretation of the results using the Long Wavelength Propagation Capability (LWPC) code in a perturbed waveguide both for the easterly and westerly propagation paths.
Abstract: A Total Solar Eclipse (TSE) provides us with an exciting opportunity to study the VLF propagation effects under a controlled experimental condition where the extreme ultraviolet and the X-rays from the sun are totally blocked by the moon. During the total eclipse of July 22nd, 2009, the Indian Centre for Space Physics conducted a VLF campaign to obtain the signal from a dozen of places in the Indian sub-continent. Six of these locations gave very good and noise-free data. In some of these data, the signal amplitude is found to be higher than that at non-eclipse condition, while in some other places, it is lower. We present the results of our campaign and give an interpretation of the results using the Long Wavelength Propagation Capability (LWPC) code in a perturbed waveguide both for the easterly and westerly propagation paths.

25 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present evidence of unusual very low frequency (VLF) signal amplitude variation during the devastating earthquake of magnitude 9.0 which occurred at Honshu, in Japan on 11 March, 2011.
Abstract: We present evidence of unusual Very Low Frequency (VLF) signal amplitude variation during the devastating earthquake of magnitude 9.0 which occurred at Honshu, in Japan on 11 March, 2011. We use the SoftPAL very low frequency receiver placed at Ionospheric and Earthquake Research Centre of Indian Centre for Space Physics, located at Sitapur (Lat. 22°30′N, Long. 87°47′E). We observe significant changes in signal amplitude from JJI (Lat. 32°05′N, Long. 131°51′E) station transmitting at a frequency of 22.2 kHz prior to the earthquake. We analyze signal amplitude for almost 2 weeks to establish a possible seismo–ionospheric correlation. We observe significant shift of the sunrise terminator time up to 2 days before the earthquake and the shift is found to be maximum on the day of the earthquake. In addition, we observe unusual increase of the D-layer disappearance time during the earthquake and the value becomes maximum on the day of the earthquake. These findings generally agree with our previous findings reported elsewhere.

22 citations


Cited by
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Journal ArticleDOI
01 Apr 1964-Nature
TL;DR: Junge as mentioned in this paper discusses air chemistry and radioactivity, and discusses the relationship between air chemistry, radioactivity and air physics, and shows that air chemistry can be viewed as a special case of radioactivity.
Abstract: Air Chemistry and Radioactivity By Christian E. Junge. (International Geophysics Series, Vol. 4.) Pp. xii + 382. (New York: Academic Press, Inc.; London: Academic Press, Inc. (London), Ltd., 1963.) 96s. 6d.

165 citations

Journal ArticleDOI
TL;DR: In this article, the authors reproduce the deviation in VLF signal strength during solar flares by numerical modeling using GEANT4 Monte Carlo simulation code to compute the rate of ionization due to a M-class flare and a Xclass flare.
Abstract: . X-ray photons emitted during solar flares cause ionization in the lower ionosphere (~60 to 100 km) in excess of what is expected to occur due to a quiet sun. Very low frequency (VLF) radio wave signals reflected from the D-region of the ionosphere are affected by this excess ionization. In this paper, we reproduce the deviation in VLF signal strength during solar flares by numerical modeling. We use GEANT4 Monte Carlo simulation code to compute the rate of ionization due to a M-class flare and a X-class flare. The output of the simulation is then used in a simplified ionospheric chemistry model to calculate the time variation of electron density at different altitudes in the D-region of the ionosphere. The resulting electron density variation profile is then self-consistently used in the LWPC code to obtain the time variation of the change in VLF signal. We did the modeling of the VLF signal along the NWC (Australia) to IERC/ICSP (India) propagation path and compared the results with observations. The agreement is found to be very satisfactory.

49 citations

Journal ArticleDOI
TL;DR: In this paper, the amplitude of the nighttime VLF signals anomalously fluctuated 4 days before the Indian Navy station VTX received an earthquake of magnitude 7.4 at Southwestern Pakistan (latitude 28.9°N, longitude 64°E).
Abstract: We have presented the result of the analysis of the nighttime VLF signals transmitted from the Indian Navy station VTX (latitude 8.43°N, longitude 77.73°E) at 19.2 kHz and received at Kolkata (latitude 22.57°N, longitude 88.24°E). On 18th January, 2011 an earthquake of magnitude 7.4 occurred at Southwestern Pakistan (latitude 28.9°N, longitude 64°E). We have analyzed the nighttime VLF signals for 2 weeks around 18th of January, 2011 to see if there have been any precursory effects of this earthquake. We have found that the amplitude of the nighttime VLF signals anomalously fluctuated 4 days before the earthquake. This agrees well with our previous findings based on the analysis of 1 year of earthquake data.

48 citations

Journal ArticleDOI
TL;DR: In this article, the effect of solar X-ray radiation on the ionospheric D-region was investigated and the effective electron recombination coefficient (αeff) at solar flare peak region was calculated.
Abstract: Excess solar X-ray radiation during solar flares causes an enhancement of ionization in the ionospheric D-region and hence affects sub-ionospherically propagating VLF signal amplitude and phase. VLF signal amplitude perturbation (ΔA) and amplitude time delay (Δt) (vis-a-vis corresponding X-ray light curve as measured by GOES-15) of NWC/19.8 kHz signal have been computed for solar flares which is detected by us during Jan–Sep 2011. The signal is recorded by SoftPAL facility of IERC/ICSP, Sitapur (22∘ 27′N, 87∘ 45′E), West Bengal, India. In first part of the work, using the well known LWPC technique, we simulated the flare induced excess lower ionospheric electron density by amplitude perturbation method. Unperturbed D-region electron density is also obtained from simulation and compared with IRI-model results. Using these simulation results and time delay as key parameters, we calculate the effective electron recombination coefficient (αeff) at solar flare peak region. Our results match with the same obtained by other established models. In the second part, we dealt with the solar zenith angle effect on D-region during flares. We relate this VLF data with the solar X-ray data. We find that the peak of the VLF amplitude occurs later than the time of the X-ray peak for each flare. We investigate this so-called time delay (Δt). For the C-class flares we find that there is a direct correspondence between Δt of a solar flare and the average solar zenith angle Z over the signal propagation path at flare occurrence time. Now for deeper analysis, we compute the Δt for different local diurnal time slots DT. We find that while the time delay is anti-correlated with the flare peak energy flux ϕmax independent of these time slots, the goodness of fit, as measured by reduced-χ2, actually worsens as the day progresses. The variation of the Z dependence of reduced-χ2 seems to follow the variation of standard deviation of Z along the Tx-Rx propagation path. In other words, for the flares having almost constant Z over the path a tighter anti-correlation between Δt and ϕmax was observed.

48 citations

Journal ArticleDOI
TL;DR: In this article, the amplitude variation of the diurnal signal at each of these receiving stations in winter and summer was compared and the results generally agree with the signal shapes obtained using the long wave propagation capability code based on mode propagation through the Earth-ionosphere cavity.
Abstract: We have carried out 2 week-long campaigns in Indian winter and summer to study VLF signals from the Indian navy transmitter (VTX) operating at 18.2 kHz. We have used more than a dozen of receivers scattered throughout the Indian sub-continent in each of these campaigns. To our knowledge, this is the largest campaign of its kind in this region. The propagation paths range from 500 km to almost 3,000 km covering an area of about 4 million sq km. We have presented the results of the amplitude variation of the diurnal signal at each of these receiving stations in winter and summer and compare them. We have clearly found the non-reciprocity of the east to west and west to east propagation. Our results generally agree with the signal shapes obtained using the long wave propagation capability code based on mode propagation through the Earth-ionosphere cavity.

45 citations