S. S. De

University of Calcutta, Kolkata, Bengal, India

Are you S. S. De?

Claim your profile

Publications (86)59.75 Total impact

  • Source
    Indian Journal of Radio and Space Physics. 12/2013; 42(6):397-403.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Some studies on the variations of integrated field intensity of sferics (IFIS) at 9 kHz are carried out at Mirik (lat 26.9°N, long 88.2°E), a hilly place of North-East India, under different seasonal conditions during January -December 2011. The recorded data are analyzed and interpreted. During locally clear days and nights, IFIS provides a regular behaviour, i.e. field strength remains constant but decreases gradually after the onset of rain. During short period showers, IFIS exhibits a sudden rise and gradual fall. An irregular variation in IFIS is observed with the coverage of roof height cloud mass. 1 Introduction Thunderstorms generate and separate electrical charges, whereas lightning neutralizes electrical charges. Simultaneous processes are operating within the environment of convective clouds that affect cloud electrification 1 . Charging of thunderclouds may be initiated by inductive or non-inductive processes. An inductive process needs pre-existing electric field to induce charges on a particle so that when it rebounds from another charge, the field gets enhanced. Within the atmosphere, the fair weather electric field resulting from positive charges in the atmosphere and negative charges on the ground could be considered as the pre-existing field 2 . Satellite and air-borne instruments demand some other processes of charging. Non-inductive processes are based on collisions between graupel particles and cloud-ice particles and on the selectivity to transfer charge of a certain polarity to other particles. Here, charge transfer occurs when ice crystals collide with simulated graupel particles within a cloud of super cooled water droplets 3 . In a thundercloud, the smaller ice-crystals are charged positively and move upward and the larger graupel particles are charged negatively which descend relative to the smaller particles 3,4 . This physical situation depends on the prevailing conditions of temperature, liquid water content and
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The paper deals with the analyses of the atmospheric vertical potential gradient (PG) from the ground for 90 fair weather days during 2006–2009 measured at Kolkata (Lat: 22.56°N). The variations of PG have been studied extensively to investigate their values during monsoon and winter seasons. Higher values of PG at Kolkata are observed due to higher abundance of pollutant particles. The observed PG are compared with the results of Potsdam station (Lat: 52°N) and Johannesburg station (Lat: 26°S), with 9 years data and 2 years data respectively. The correlations studies are carried out among PG, PDC (Point Discharge Current) as well as negative and positive carrier conductivities. The corresponding correlation coefficients are obtained as 0.93, −0.842 and −0.844.
    Journal of Atmospheric and Solar-Terrestrial Physics 12/2013; s 105–106:135–141. · 1.42 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The effect of solar eclipse of July 22, 2009, obscuring up to 91 %, upon the value of point discharge current (PDC) has been reported in this paper. The observation had been taken from Kolkata (Lat. 22.56°N, Long. 88.5°E). During the eclipse period, significant variations in the magnitude of PDC were observed than their average value for the same period in other days. The average value of the PDC for the successive ±10 days adjacent to the solar eclipse day was about 2.253 A.U. (Arbitrary Unit), while the minimum value showed about 2.242 A.U. at the time of greatest phase at 06:26.4 IST (Indian Standard Time). The results are mainly interpreted in terms of changes of the conductivity of the medium during the solar eclipse.
    Earth Moon and Planets 11/2013; · 0.83 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Measurement of atmospheric electric potential gradient (PG) at Kolkata (latitude 22.56°N, longitude 88.5°E) during solar eclipse of 22 July 2009 has been carried out. The effects of solar eclipse on the potential gradient are presented in the paper, which show significant changes in the value during the eclipse period than their ambient values for the same period on other days. It shows that the PG value decreases about 38% during the eclipse period with some irregular variation during rest of the day. The results of measurements of ground level conductivity, temperature and relative humidity are also presented and discussed on the basis of change in conductivity due to eclipse, effects of global thunderstorm centers and local effects. 1 Introduction The atmospheric electric potential gradient near the Earth's surface is governed by global thunderstorm and lightning activities 1,2 . These put the Earth-ionosphere waveguide into resonance producing various characteristic spectra 3 . This potential gradient also depends on local environmental factors. There exists a correlation between the local potential gradient and worldwide thunderstorm distribution. The disturbances in the ionosphere during solar eclipse are reported in terms of VLF amplitude of sferics, amplitude and phase changes in transmitted signals 4-6 as well as changes in the Earth's near surface vertical electric potential gradient 7,8 . The variation of air temperature, electric field, current density and conductivity over the surface of the Earth at tropical latitudes (± 25º) and temperate latitudes (± 60º) are interrelated with the solar radiations, global lightning activity and concentration of the aerosol content in the lower ionosphere 9-15 . Below 90 km altitude, the electron concentration is controlled by photo-ionization, recombination and different attachment-detachment processes leading to the formation and destruction of negative ions.
    08/2013; 42:251-258.
  • Dataset: MASA Paper
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The effects of 2009 Leonid Meteor Shower upon the two VLF subionospheric transmitted signals and vertical electric potential gradient from the ground surface have been studied from Kolkata (Lat: 22.56�N, Long: 88.5�E) on November 17, 2009. The received signals showed their peak values when ZHR (Zenithal Hourly Rate) was highest. Some typical variations in the outcome of these measurements during the meteor showers will be presented in this paper.
    Earth Moon and Planets 01/2012; 108(2):111-121. · 0.83 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The development of a neurocomputing technique to forecast the average winter shower in India has been modeled from 48 years of records (1950–1998). The complexities in the rainfall–sea surface temperature relationships have been statistically analyzed along with the collinearity diagnostics. The presence of multicollinearity has been revealed and a variable selection has been executed accordingly. The absence of persistence has also been revealed. For this reason, an Artificial Neural Net Model as a predictive tool for the said meteorological event in the form of a Multiple Layer Perceptron has been generated with a sea surface temperature anomaly and monthly average winter shower data over India during the above period. After proper training and testing, a Neural Net model with small prediction error is developed and the supremacy of the Artificial Neural Net over conventional statistical predictive procedures has been established statistically.
    Journal of Hydroinformatics 01/2012; · 1.15 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The precursory effects from several earthquakes upon the two subionospheric transmitted signals, one 19.8 kHz from North West Cape, Australia (lat: 21.821S; long: 114.161E) and the other 40 kHz from Fukushima, Japan (lat: 37.371N; long: 140.851E), are studied from the recorded data at Kolkata (lat: 22.561N, long: 88.51E). Some spiky transients are observed. Spike height and spike intensity are dependent on the depth of epicenter, distance of the epicenter from the propagation path and also from the observing station. The earthquakes occurring during the period of March 20, 2010–May 31, 2010 have been considered. Among 22 earthquakes, the analyses are made for only 13 earthquakes all having M4 6. Earthquake induced time-series observations of the spikes and their analyses are presented in this paper. Attempts are made to determine the possible visual study between M/D ratio and spike height. From this ratio, the probable sensitivity of the signals from different earthquakes may be studied.
    Journal of Atmospheric and Solar-Terrestrial Physics 01/2012; 81-82:20-26. · 1.42 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Remarkable effects on the records on Integrated Field Intensity of Atmospherics (IFIA) over Kolkata (latitude: 22.56° N, longitude: 88.5° E) at 3 kHz and 9 kHz are observed due to severe electrical activity in a thunderstorm, AILA, followed by severe thundershowers and lightning. The analyses and evaluation of the recorded data have been presented here.
    General Assembly and Scientific Symposium, 2011 XXXth URSI; 09/2011
  • Source
    G. Chattopadhyay, S.S. De
    [Show abstract] [Hide abstract]
    ABSTRACT: Purpose of the present paper is to examine the predictability of the occurrence of the severe pre-monsoon thunderstorm over Gangetic West Bengal. Instead of considering various meteorological predictors, the daily total ozone concentration is chosen as the predictor because of the influence of tropospheric as well as stratospheric ozone on the genesis of meteorological phenomena. Considering the occurrence/non-occurrence of thunderstorm in the pre-monsoon season (March-May) of the year 2005 as the dichotomous time series{X<sub>t</sub>} that realizes 0 and 1 for non-occurrence and occurrence of TS respectively, a first order two state (FOTS) Markov dependence is revealed within this time series.
    General Assembly and Scientific Symposium, 2011 XXXth URSI; 09/2011
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Auroral electric field is a probable source of Atmospheric Gravity Waves (AGW) in the thermospheric region of Auroral zone of the ionosphere and associated Traveling Ionospheric Disturbances (TID). This field is considered to be active through Lorentz force and Joule dissipation that influence the neutral gas of the medium through collision. The process introduces the short-range gravity waves. The expressions for the low frequency part of the fractional pressure variations have been derived within the auroral region of the ionosphere. The results of numerical analyses are presented graphically.
    General Assembly and Scientific Symposium, 2011 XXXth URSI; 09/2011
  • Source
    S. Paul, S.S. De
    [Show abstract] [Hide abstract]
    ABSTRACT: Schumann resonances (SR) observations from a tropical region near Kolkata at the estuary of the river Ganges merging into the Bay-of-Bengal (21.48° N, 88.61° E) are being made frequently. Several Q-bursts spectra are observed. Strong ELF transients are detected in the recorded data of SR. The dynamic evolution of electric and magnetic field components of the Q-bursts will be presented in this paper. Time series evolutions of signals of several Q-bursts are analyzed in the present study. It is observed that, the Q-burst amplitudes from 1 to 300 Hz of Q-bursts spectra for 1 sec FFT reaches about -47 dB near the first mode of SR frequency. This shows that Q-burst has the tendency to dominate within 1 to 300 Hz.
    General Assembly and Scientific Symposium, 2011 XXXth URSI; 09/2011
  • Source
    D.K. Haldar, S.S. De
    [Show abstract] [Hide abstract]
    ABSTRACT: Enhanced tropical convection is associated with increased upper-tropospheric relative humidity. The positive co-relationship between deep convection and upper-tropospheric humidity is observed for both regional and temporal variations over a wide range of space and time scales. The regions of increased upper-tropospheric moisture are found to be strongly correlated with an enhanced greenhouse trapping, although the effects of lower-tropospheric moisture and temperature lapse rate are also observed to be important. The greenhouse effect of water vapour increases sharply when temperature increases, leading to a positive feed back for climate change. Upper-tropospheric water-vapour (UTWV) variability and global lightning activity are closely linked suggesting that upper-tropospheric water-vapour changes can be inferred from the records of global lightning activity. The continental deep-convective thunderstorms could transport large amount of water vapour into the upper troposphere, which would dominate the variations of global UTWV while producing most of the lightning on Earth. Global lightning produces Schumann resonance modes, which are trapped in the Earth-ionospheric waveguide. As there are approximately 50-100 lightning flashes per second around the globe, the variability of the intensity of the Schumann resonances represents a continuous measure of the variability of global lightning activity which is dependent on UTWV. Thus monitoring of SR would provide a tool for time-tracking UTWV changes which will contribute to a better understanding of the processes affecting climate change. The correlation between troposheric water content and Schumann Resonance field can be explored using data of several years, which is still lacking to the world researchers. From the observed nature of correlation of time series data, a model will be built which will be made useful to forecast the water vapour content from the observed value of Schumann Resonance data. Climatic conditi- - on would be forecasted using SR data with the sequence below: SR data ⇒ Water vapour content ⇒ climate forecasting.
    General Assembly and Scientific Symposium, 2011 XXXth URSI; 09/2011
  • [Show abstract] [Hide abstract]
    ABSTRACT: A model is developed to study the carrier lifetime and quantum efficiency in heavily doped InGaAsP. In the analysis, bandgap narrowing, carrier degeneracy, and nonparabolicity of the band structure are considered as heavy doping effects. The variations of carrier lifetime and quantum efficiency with nominal current density at a given temperature are studied through numerical analysis.
    Canadian Journal of Physics 02/2011; 71:582-585. · 0.90 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Some anomalies are observed in the subinospheric VLF electromagnetic (EM) signals at 19.8 kHz transmitted from North West Cape, Australia (lat: 21.82° S; long: 114.16° E) and 40 kHz from Fukushima, Japan (lat: 36.18° N, long: 139.85° E), recorded by VLF receivers near Kolkata (lat: 22.56° N, long: 88.5° E) during the occurrence of the two earthquakes at Andaman Island (lat:14.018° N, long: 92.92° E), India and other at South Coast of Honsu (lat: 34.78° N, long: 138.27° E), Japan. The analyses of these seismo-ionospheric VLF EM anomalies at these two frequencies during some days before and after the occurrence of earthquake on August 11, 2009 will be presented here. VLF-LF transient variations of significant magnitude in the form of spikes are observed few days prior to the day of occurrence of the earthquakes that continued several days more, then decaying gradually and finally ceased. Signals are examined to describe their connectivity with earthquakes. The enhancements of the amplitude and frequency of the fourth mode of Schumann resonance spectra have been detected during the occurrence of the two earthquakes, which will also be reported here.
    Indian Journal of Physics 01/2011; 85(3):447-470. · 1.79 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The observation and analyses of pre-seismic VLF electromagnetic (EM) signals recorded by VLF receivers at frequencies 5, 7, 9 and 12 kHz on November 16, 2008 over Kolkata (Lat. 22.56º   N, Long. 88.5º E) during the large earthquake at Minahasa, Sulawesi, under Indonesia (Lat. 1.27º N, Long. 122.09º E) will be presented. Spiky variations of signals are observed few days prior to the day of occurrence of the earthquake which continued several days more, then decayed gradually and eventually ceased. These signals are critically examined to delineate their correlation with earthquake. The time variability of natural EM signals in the VLF band is juxtaposed with the pre-seismic records.
    Romanian Journal of Physics 01/2011; 56:1208-1227. · 0.75 Impact Factor
  • Source
    Model Assisted Statistics and Applications 01/2011; 6:357-368.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The variation of the first Schumann resonance (SR) frequency spectra observed from the recorded data over Kolkata (22.56°N, 88.5°E) during a solar proton event (SPE) on July 14, 2000 has been presented. It shows increase in frequency during X-ray bursts and decrease during the period of occurrence of an SPE. The results from some other locations for the same event are also reported. The severe X-ray bursts recorded just before the proton event exhibit enhancement in frequency of the first mode due to enhancement of ionization in the D-region of the ionosphere. Some attempts are made to explain the observed variation during solar proton events in terms of the perturbations within the Earth–ionosphere waveguide on the basis of two-layer-model.
    Journal of Atmospheric and Solar-Terrestrial Physics 01/2010; 72. · 1.42 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The outcome of the results of some analyses of electromagnetic emissions recorded by VLF receivers at 6 kHz and 9 kHz over Agartala, Tripura, the North-Eastern state of India (Lat. 23° N, Long. 91.4° E) during the large earthquake at Muzaffarabad (Lat. 34.53° N, Long. 73.58° E) at Kashmir under Pakistan have been presented here. Spiky variations in integrated field intensity of atmospherics (IFIA) at 6 and 9 kHz have been observed 10 days prior (from midnight of 28 September 2005) to the day of occurrence of the earthquake on 8 October 2005 and the effect continued, decayed gradually and eventually ceased on 16 October 2005. The spikes distinctly superimposed on the ambient level with mutual separation of 2–5 min. Occurrence number of spikes per hour and total duration of their occurrence have been found remarkably high on the day of occurrence of the earthquake. The spike heights are higher at 6 kHz than at 9 kHz. The results have been explained on the basis of generation of electromagnetic radiation associated with fracture of rocks, their subsequent penetration into the Earth's atmosphere and finally their propagation between Earth-ionosphere waveguide. The present observation shows that VLF anomaly is well-confined between 6 and 9 kHz.
    Natural hazards and earth system sciences 01/2010; · 1.75 Impact Factor