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Agartala, India

De B.K.,Tripura University | De S.S.,University of Calcutta | Bandyopadhyay B.,University of Calcutta | Pal P.,Tripura University | And 4 more authors.
Terrestrial, Atmospheric and Oceanic Sciences | Year: 2011

The results from the measurements of some of the fundamental parameters (amplitude of sferics and transmitted signal, conductivity of lower ionosphere) of the ionospheric responses to the 22 July 2009 solar eclipse (partial: 91.7%) are shown. This study summarizes our results from sferics signals at 81 kHz and subionospheric transmitted signals at 19.8 and 40 kHz recorded at Agartala, Tripura (latitude: 23°N, longitude: 91.4°E). We observed significant absorption in amplitude of these signals during the eclipse period compared to their ambient values for the same period during the adjacent 7 days. The signal strength along their propagation paths was controlled by the eclipse associated decrease in ionization in the D-region of the ionosphere. Waveguide mode theory calculations show that the elevation of the height of lower ionosphere boundary of the Earth-ionosphere waveguide to a value where the conductivity parameter was 106 unit. The absorption in 81 kHz sferics amplitude is high compared to the absorption in the amplitude of 40 kHz signal transmitted from Japan. The simultaneous changes in the amplitudes of sferics and in the amplitude of transmitted signals assert some sort of coupling between the upper atmosphere and the Earth's near-surface atmosphere prevailing clouds during solar eclipse. Source

De S.S.,University of Calcutta | De B.K.,Tripura University | Bandyopadhyay B.,University of Calcutta | Paul S.,University of Calcutta | And 5 more authors.
Romanian Reports of Physics | Year: 2011

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. 22.56° N, Long. 88.5° E) during the large earthquake at Minahasa, Sulawesi, under Indonesia (Lat. 1.27° N, Long. 122.09° 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. Source

De S.S.,University of Calcutta | Paul S.,University of Calcutta | Barui S.,University of Calcutta | Pal P.,Maharaja Bir Bikram College | And 3 more authors.
Journal of Atmospheric and Solar-Terrestrial Physics | Year: 2013

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. © 2013 Elsevier Ltd. Source

Chaudhuri P.S.,Tripura University | Pal T.K.,Rubber Research Institute of India | Nath S.,Maharaja Bir Bikram College | Dey S.K.,Rubber Research Institute of India
Journal of Environmental Biology | Year: 2012

An incubation experiment was conducted to study the changes that occur in organic carbon content, phosphorous and potassium availability and other soil properties with ingestion of soil mixed with rubber leaf litter and cow dung by five earthworm species viz. Pontoscolex corethrurus, Drawida assamensis, Drawida papillifer papillifer, Eutyphoeus comillahnus and Metaphire houlleti of rubber plantation in Tripura (India). Due to earthworm activity organic 0(1.56-1.63%) and available P (14.71-27.60 mg 100 g-1) and K (43.50-49.0 mg 100 g-1) content of the soil increased significantly (p Source

Chaudhuri P.S.,Maharaja Bir Bikram College | Nath S.,Maharaja Bir Bikram College
Journal of Environmental Biology | Year: 2011

Studies on community structures of earthworms of rubber (Hevea brasiliensis) plantations and their adjacent mixed forests in West Tripura (India) revealed that both the studied sites harvoured 10 earthworm species. Nine species (Pontoscolex corethrurus, Kanchuria sp 1, Metaphire houlleti, Drawida papillifer papillifer, Drawida assamensis, Gordiodrilus elegans, Eutyphoeus assamensis, Eutyphoeus comillahnus and Eutyphoeus gigas) were common to both. While Octochaetona beatrix was found only in the rubber plantations, Dichogaster affinis was restricted to the mixed forest only. Earthworms were found mostly within 15 cm depth of soils having mean temperature of 27°C, moisture of 23%, pH of 4.57, organic matter of 1.34% and water holding capacity of 36%. Mean earthworm density in rubber plantations (115 ind. m -2) was significantly higher (p = 0.003, t = 3.83) than that in the mixed forests (69 ind. m -2) due to dominance of Pontoscolex corethrurus, an exotic species. Numbers of dominant species were two (P. corethrurus and D. assamensis) in the rubber plantations and five (P. corethrurus D. assamensis, D. papillifer papillifer, M. houlleti and Kanchuria sp 1) in the mixed forests. Compared to the mixed forests, significantly low (p<0.05) Shannon diversity index (H) and species evenness and high index of dominance in the rubber plantation were evaluated. © 2011 Triveni Enterprises. Source

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