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91.
An investigation on the temporal and spatial variation of ozone using the total column ozone (TCO) values during the cyclonic activities over North Indian Ocean (NIO) is carried out during the period from 1997 to 2012. The stepwise variation of TCO during the passage of the tropical cyclones over the Bay of Bengal and the Arabian Sea of the NIO is examined. The anomalies in TCO are estimated at each step of the life span of the cyclones starting from the genesis to landfall stages. The result reveals that the TCO values are quite high prior to the formation of the depression over NIO; however, at the stage of cyclogenesis it decreases which, with the increase in the intensity of the cyclones, further decreases and becomes minimum near the coast during the landfall. The maximum negative anomaly in TCO is observed for maximum intensity of the tropical cyclones as well as during the landfall. The result further shows that when the cyclones die out after the landfall the TCO regains the normal value. It is further observed that the reduction in TCO enhances the accumulated cyclone energy over NIO. The result finally shows that, the higher the energy of the cyclones, the lower becomes the stratospheric warming, that is, the higher the stratospheric cooling. 相似文献
92.
Wind observations made at Gadanki (13.5°N) by using Indian MST Radar for few days in September, October, December 1995 and January, 1996 have been analyzed to study gravity wave activity in the troposphere and lower stratosphere. Horizontal wind variances have been computed for gravity waves of period (2–6) h from the power spectral density (PSD) spectrum. Exponential curves of the form eZ/H have been fitted by least squares technique to these variance values to obtain height variations of the irregular winds upto the height of about 15 km, where Z is the height in kilometers. The value of H, the scale height, as determined from curve fitting is found to be less than the theoretical value of scale height of neutral atmosphere in this region, implying that the waves are gaining energy during their passage in the troposphere. In other words, it indicates that the sources of gravity waves are present in the troposphere. The energy densities of gravity wave fluctuations have been computed. Polynomial fits to the observed values show that wave energy density increases in the troposphere, its source region, and then decreases in the lower stratosphere. 相似文献
93.
Pratik Dutta Santanu Bhowmik Saumitra Das 《International Journal of Coal Geology》2011,85(3-4):289-299
Complete sorption isotherm characteristics of methane and CO2 were studied on fourteen sub-bituminous to high-volatile bituminous Indian Gondwana coals. The mean vitrinite reflectance values of the coal samples are within the range of 0.64% to 1.30% with varying maceral composition. All isotherms were conducted at 30 °C on dry, powdered coal samples up to a maximum experimental pressure of ~ 7.8 MPa and 5.8 MPa for methane and CO2, respectively.The nature of the isotherms varied widely within the experimental pressure range with some of the samples remained under-saturated while the others attained saturation. The CO2 to methane adsorption ratios decreased with the increase in experimental pressure and the overall variation was between 4:1 and 1.5:1 for most of the coals. For both methane and CO2, the lower-ranked coal samples generally exhibited higher sorption affinity compared to the higher-ranked coals. However, sorption capacity indicates a U-shaped trend with rank. Significant hysteresis was observed between the ad/desorption isotherms for CO2. However, with methane, hysteresis was either absent or insignificant. It was also observed that the coal maceral compositions had a significant impact on the sorption capacities for both methane and CO2. Coals with higher vitrinite contents showed higher capacities while internite content indicated a negative impact on the sorption capacity. 相似文献
94.
Borehole direct current (dc) resistivity problems are solved using finite difference method (FDM) primarily to extend the log interpretation in the two-dimensional (2D) domain. Transitional invaded zone, flushed zone, uncontaminated zone, shoulder beds and borehole filled with mud are simulated simultaneously in the model. Linear variation of resistivity is assumed for transitional invaded zone. Normal, lateral and modified laterolog7 (LL74) electrode configuration (discussed in the text) responses were computed using expanding rectangular grid system. LL74 responses with variable geometric factor did show some superiority over the conventional normal and lateral for conductive target beds sandwiched between the resistive beds. For relatively small borehole diameter, all three probes can detect resistive target bed satisfactorily. However, for highly conductive mud both LL74 and normal electrode configuration fail to detect any signal from the target bed. Bypassing effect of the current for LL74 is more than that in normal log. Lateral log shows a signal of conductive invaded zone generated by the conductive mud. Bucking current ratio peaks and the geometric factor peaks in LL74 can detect the bed boundaries. 相似文献
95.
96.
The 4th IPCC report highlights the increased vulnerability of the coastal areas from floods due to sea-level rise (SLR).
The existing coastal flood control structures in Bangladesh are not adequate to adapt these changes and new measures are urgently
necessary. It is important to determine the impacts of SLR on flooding to analyse the performance of the existing structures
and corresponding impact to plan for suitable adaptation and mitigation measures to reduce the impacts of floods on coastal
zone. The study aims to develop a comprehensive understanding of the possible effects of SLR on floods in the coastal zone
of Bangladesh. A hydrodynamic model, which is a combination of surface and river parts, was utilized for flood simulation.
The tool was applied under a range of future scenarios, and results indicate both spatial variability of risk and changes
in flood characteristics between now and under SLR. Estimated impact on population, infrastructure and transportation is also
exposed. These types of impact estimation would be of value to flood plain management authorities to minimize the socio-economic
impact. 相似文献
97.
Runcie P. Mathews Suryakant M. Tripathi Santanu Banerjee Suryendu Dutta 《Journal of the Geological Society of India》2013,82(3):236-248
Extensive Cenozoic lignite-bearing sediments in the western part of Kutch, western India provide a unique opportunity to study the floral diversity at a crucial time of early Eocene Climatic Optimum (EECO). Rock samples representing a lignite-bearing sequence from the open cast mine at Matanomadh, Gujarat, western India were collected to study the palynofloral composition and to interpret the palaeoclimate and environment of deposition. The sequence mainly composed of lignites, shales and calcareous mudstones yielded rich assemblage consists of pteridophytic spores (7 genera, 10 species), angiosperm pollens (20 genera, 26 species), fungal remains (14 genera, 16 species) and dinoflagellate cysts. The palynofloral assemblage is marked with dominance of angiospermic pollen, particularly those having affinity with the family Arecaceae. Occurrence of fungal remains in high abundance is also noticed. Based on palynomorph contents, the studied sequence is divisible into two palynozones. It is inferred that lower part of the sequences was deposited in a near-shore environment with intermittent marine incursions whereas the depositional regime of upper part was shallow marine. The climate is found to be tropical-subtropical, humid with heavy precipitation during the deposition of Matanomadh lignite-bearing sequence. 相似文献
98.
Suryendu Dutta Michael Steiner Santanu Banerjee Bernd-Dietrich Erdtmann Silambuchelvan Jeevankumar Ulrich Mann 《Journal of Earth System Science》2006,115(1):99-112
Chuaria circularis (Walcott 1899) from the Suket Shale of the Vindhyan Supergroup (central India) has been reinvestigated for its morphology
and chemical composition using biostatistics, electron microscopy and pyrolysis-gas chromatography. Morphology and microscopic
investigations provide little clues on the specific biological affinity ofChuaria as numerous preservational artifacts seem to be incorporated. On the contrary, the predominance of η aliphatic pyrolysates
of presently studiedChuaria from India rather supports an algal affinity. Moreover, the reflectance ofC circularis can be used to obtain a comparative maturity parameter of the Precambrian sediments. The review of the age and geographical
distribution ofC circularis constrains that this species cannot be considered as an index fossil for the Proterozoic time. 相似文献
99.
Subash Chandra V. A. Rao N. S. Krishnamurthy S. Dutta Shakeel Ahmed 《Hydrogeology Journal》2006,14(6):1042-1051
An integrated study was carried out to investigate the subsurface geological conditions in a hard rock environment, with the aim of identifying zones with groundwater resource potential. The study, in Bairasagara watershed, Karnataka, India, considered geomorphology, water level, resistivity imaging, self potential, total magnetic field and susceptibility. The signatures due to lineaments have been clearly identified and their role in groundwater movement has been documented. Synthetic simulation methods were used to model the electrical response of the lineament using finite differential modeling scheme. The inverted image of the field data is compared with the synthetic image and iteration were performed on the initial model until a best match was obtained resulting on the generation of the calibrated resistivity image of the subsurface. Resistivity imaging revealed that the dykes are weathered/fractured to a depth of 6–8 m and are compact at deeper levels, and that they behave as barriers to groundwater movement, yet facilitate a good groundwater potential zone on the upgradient side. The results of magnetic surveys were utilized in differentiating granites and dolerite dykes with an insignificant resistivity contrast. Geomorphological expression alone cannot reveal the groundwater potential associated with a lineament. However, characterizing the nature of the feature at depth with integrated geophysical methods provides essential information for assessing that potential.The online version of the original article can be found at 相似文献
100.