Multitechnique studies of nor’wester using electrical and meteorological parameters     

A. B. Bhattacharya 《Annales Geophysicae》1994,12(2-3):232-239

Radar observations of nor’wester (premonsoon thunderstorm) as experienced over the Gangetic West Bengal and the integrated field intensity of atmospherics (IFIA) at 10, 20 and 30 kHz recorded over the tropical station at Calcutta have been analysed. The records of IFIA reveal that, during nor’wester, the enhancement in the signal level occurs in three different stages: (i) gradual rise of atmospherics (GRA), (ii) first sudden enhancement of atmospherics (SEA₁) and (iii) second sudden enhancement of atmospherics (SEA₂. Their respective occurrences have been found to be prevalent in pre-noon, latenoon and afternoon hours of a day. Of the three stages, GRA and SEA₁ have been found to occur before the onset of thunderstorm, while SEA₂ may even occur after its onset. A comparative study reveals that the precipitation during premonsoon thunderstorms is associated with the second sudden enhancement, while it is associated with the steady recovery of IFIA during the monsoon and postmonsoon thunderstorms. The characteristics of the first nor’wester of every year have been critically examined with an additional consideration of simultaneous radiosonde records. A probable explanation has been made in terms of the distribution of the effective sources at such times around the observing site.  相似文献   

Refinement of geothermobarometry for cordierite granulites     

S Bhattacharya 《Journal of Earth System Science》1993,102(4):537-545

Refined geothermobarometers are presented for cordierite granulites. The refinement was achieved by using internally consistent thermodynamic datasets. Improved calibrations have been demonstrated for a number of granulite areas. Also, the usefulness of the improved geobarometer in identifying decompression paths has been discussed.  相似文献   

High-pressure silicate liquidus data: Retrieval of partial molar enthalpy and partial molar entropy of mixing,a test of the regular solution formulation,and comments on theP-T modelling of ascending magmas     

Amalbikash Mukherjee  Abhijit Bhattacharya 《Earth and Planetary Science Letters》1980,49(2):231-236

The activity of a silicate liquid component in a melt at an elevated liquidus temperature and pressure may be expressed analytically in terms of the 1-bar liquidus temperature activity and functions of the partial molar volume and partial molar enthalpy of mixing. Alternatively, the activity of the elevated (i.e. higherP-T) liquidus may be expressed in terms of the difference of heat content, heat capacity, entropy and volume of the component in the crystalline form and in the melt. Equating these two expressions, the partial molar enthalpy of mixing and there-from the partial molar entropy of mixing may be determined, provided the liquidus temperatures of the phase in question at both 1 bar and higher pressure and at a constant melt composition are known. Several such retrievals for CaMgSi₂O₆, Mg₂SiO₄, NaAlSi₃O₈, and TiO₂ from experimental phase equilibrium data are presented. It is argued that as the partial molar enthalpy of mixing generally has large values, the regular solution formulation on the basis of a constant function of the activity coefficient would lead to erroneousP-T estimates for ascending magmas.  相似文献   

Implications of north pacific plate tectonics in central Alaska: Focal mechanisms of earthquakes     

B. Bhattacharya  N. N. Biswas 《Tectonophysics》1979,53(1-2)

The focal mechanisms for 86 selected earthquakes (3.0 m_b 5.5) located in central Alaska have been investigated from P-wave first motions; the data were gathered by local seismic networks. The results show a depth-dependent characteristic to the fault-plane solutions. For earthquakes having focal depths shallower than 60–70 km, the focal mechanisms indicate either strike-slip or normal faults, while for earthquakes with foci at intermediate depths the focal mechanisms correspond to thrust faults. The nature of the seismicity indicates the hinge line of the Pacific lithospheric plate under the study area to be striking N17°E from Cook Inlet towards interior Alaska. The comparison of the focal mechanisms with the seismicity shows that the strike-slip and normal faults are the predominant processes of stress release along the shallow section of the plate. The earthquakes with intermediate foci systematically occur along the inclined section of the plate. If the gently dipping nodal planes for these earthquakes are chosen as the fault planes, the focal mechanisms correspond to underthrust motions at the foci. In these, the slip vectors are oriented either to the west or north with the resultant being in the N30°W direction. The tension axes for the underthrust solutions are also found to be parallel to the local dip of the plate, indicating that the subducted plate in interior Alaska is undergoing gravitational sinking.  相似文献   

Photogeological mapping for regional studies of the Vindhyan rocks around Bundi area,Rajasthan     

A. Bhattacharya  A. K. Roy  K. Thiyagarajan  K. K. Naik 《Journal of the Indian Society of Remote Sensing》1983,11(2):19-29

An area of 2300 sq km s has been mapped around Bundi based on aerial photo-interpretation, with selected field checks at key areas. The oldest rocks exposed are Aravallis comprising a thick pile of argillaceous sediments with thin interbeds of quartzite. The Aravalli rocks have been subjected to two phases of folding and have undergone a low grade of metamorphism. The Vindhyan rocks which comprise arenaceons, argillaceous and calcareous sediments constitute the Kaimur, Rewa and Bhander groups. These rocks occur south of the Aravallis with a faulted contact (Great Boundary Fault) for the major part, and also with unconformable contact at places. The upliftment of the Aravallis on the northern side of the Great Boundary Fault might have created the Vindhyan Basin south of it. The movement appears to have been gradual, keeping pace with the Vindhyan sedimentation, and was possibly revived even after the Vindhyan sedimentation as evidenced by the presence of folding and faulting in Vindhyans in the vicinity of the boundary fault. Strike faulting parallel to the boundary fault is very conspicious resulting in the repetition of the Vindhyan strata in the area east of Bundi. The Vindhyans of Bundi area indicate deposition of sediments in shallow water coastal barrier and lagoonal set-up as evidenced by sedimentary features such as tabular current bedding, ripple marks, huge blankets of sandstone, alternation of shale and limestone etc. Geomorphologically the area may be divided into three units namely:-(a) Pediment on Aravallis, (b) Structural hills on Vindhyan, expressing generally as hogback and cuesta ridges and strike valleys, and (c) Piedmont and alluvial plains (Chambal valley). The photo characters of the different litho-units have been described.  相似文献   

Conservation of biodiversity of the coastal resources of Sundarbans,Northeast India: an integrated approach through environmental education     

Sarkar SK  Bhattacharya AK 《Marine pollution bulletin》2003,47(1-6):260-264

The Indian Sundarbans, a diversified coastal wetland on the southern fringe of the State of West Bengal, harbors a luxuriant biodiversity and acts as a potential refuge of living marine resources. Girdled with thick mangrove foliage, this estuarine delta system offers an excellent nursery ground for most of the brackishwater finfish and shellfish. Since supply of hatchery-produced tiger prawn seed (Penaeus monodon) is highly inadequate in West Bengal, the aquaculture farms of this region largely depend on the supply from natural resources. Being motivated by a regular cash income, the majority of coastal people from Sundarbans have adopted prawn seed collection as their profession almost throughout the year as an important source of earning. The users are neither trained nor guided at any stage from collection to marketing and are fully dependent on traditional methods. They first sort out the tiger prawn seeds (mainly the postlarval stage PL 20) accounting only 0.25-0.27% of the total catch and thereafter the major portion of the haul are thrown away on the beach flats or the tidal mudflats. This wasted by-catch contains the juveniles of economic and uneconomic varieties of finfish and shellfish along with a bulk of holoplankters and meroplankters (non-target species). This practice causes several ecological and occupational consequences, namely, (i) the huge destruction of the pelagic biota that can lead to severe stock depletion as well as hamper the energy transference through the marine ecosystem food webs; (ii) constant dragging of nets along the coast and tidal creeks paves the way for soil erosion, uprooting the mangrove seedlings and saltmarsh vegetation; (iii) the water quality is deteriorating in the catchment areas due to mud erosion and (iv) due to constant contact with the seawater, the collectors are affected with waterborne diseases, skin infections, reproductive tract disease in women and many other contagious diseases.This paper, in addition to identifying the challenge to environmental quality and resource abundance, emphasizes the need for grass-root public education so that local people come to understand, support and implement sustainable resource conservation and environmental protection activities now and in the future. As a follow-up course of action, the authors have initiated a general awareness program for developing consciousness among the coastal people regarding proper use of natural resources. Initiatives are taken for educating coastal people by holding workshops and seminars with the use of educational resource materials. Exclusive awareness camps and grass root level training for coastal people are also being proposed as a future course of action by means of exhibitions, audiovisuals etc. It is proposed that local government bodies come forward to mitigate this problem with scientific and rational approaches and to take proper actions towards conservation.  相似文献   

Facies, dissolution seams and stable isotope compositions of the Rohtas Limestone (Vindhyan Supergroup) in the Son valley area, central India     

S. Banerjee  S. K. Bhattacharya  S. Sarkar 《Journal of Earth System Science》2005,114(1):87-96

The early Mesoproterozoic Rohtas Limestone in the Son valley area of central India represents an overall shallowing-upward carbonate succession. Detailed facies analysis of the limestone reveals outer- to inner-shelf deposition in an open marine setting. Wave-ripples, hummocky cross stratifications and edgewise conglomerates argue against a deep marine depositional model for the Rohtas Limestone proposed earlier. Stable isotope analysis of the limestone shows that δ¹³C and δ¹⁸O values are compatible with the early Mesoproterozoic open seawater composition. The ribbon limestone facies in the Rohtas Limestone is characterized by micritic beds, each decoupled in a lower band enriched and an upper band depleted in dissolution seams. Band-wise isotopic analysis reveals systematic short-term variations. Comparative enrichment of the heavier isotopes in the upper bands is attributed to early cementation from sea water and water derived from the lower band undergoing dissolution because of lowering of pH at depth. The short-term positive shifts in isotopic compositions in almost every upward gradational transition from a seamed band to a non-seamed band support the contention that dissolution seams here are of early diagenetic origin, although their formation was accentuated under overburden pressure.  相似文献   

Delineation of arsenic-contaminated zones in Bengal Delta, India: a geographic information system and fractal approach     

Basab Mukhopadhyay  P. K. Mukherjee  Debkumar Bhattacharya  S. Sengupta 《Environmental Geology》2006,49(7):1009-1020

Groundwater extracted from shallow aquifers in the Bengal Delta is contaminated with arsenic. The fluviodeltaic process that creates aquifers, ironically, extends its role to also contaminating them with arsenic. The arsenic distribution maps show a spatial association of arsenic-contaminated wells with palaeo/cut-off/abandoned channels. Weight-on-evidences analysis indicates that the zones of contamination occur around palaeo-channels within a corridor of 500–700 m that contains most of the contaminated wells. These corridors are interpreted to be the zone of channel shifting. Contaminated wells represent point fractal geometry that can be separated into isolated points and clusters. Clusters occur within the zone of channel shifting as obtained by weight-on-evidences analysis. Isolated points occur within floodplain or back swamp areas. Clusters and isolated point fractals are interpreted to reflect the process of arsenic release into groundwater. The migration of biomass within the permeable sandy domain of channel deposits is proposed to be the predominant process in generating clusters. The isolated points represent restricted biomass spreading in less permeable clay-silt dominated floodplains.  相似文献   

Nature, origin and evolution of the granitoid-hosted early Proterozoic copper-molybdenum mineralization at Malanjkhand, Central India – a reply     

S. C. Sarkar  S. Kabiraj  S. Bhattacharya  A. B. Pal 《Mineralium Deposita》1997,32(6):622-622

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Response of thunderstorm and lightning activity to solar modulation of atmospheric electrification     

A. B. Bhattacharya  S. K. Kar  R. Bhattacharya 《Theoretical and Applied Climatology》1997,58(1-2):95-103

Summary The influence of thunderstorms on the atmospheric radio noise field strength (ARNFS) over Kalyani (West Bengal) at 27 kHz has been analyzed over a two-year period. The results show that the median noise level decreases during the winter and reaches a maximum during the monsoon months. A comparison of the seasonal occurrence of thunderstorm-days with ARNFS indicates that both of them have similar trend over time. However, the trend is more pronounced during daytime, indicating relationship between solar activity, thunderstorms and ARNFS. In this paper, we have attempted to investigate how tropical thunderstorm and lightning activity might be responsible for the solar modulation of atmospheric electrification. The influence of ionizing radiation on the electrical global circuit of the atmosphere is also critically analyzed.With 7 Figures  相似文献