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This paper examines the small-scale solar wind turbulence driven in view of the Alfvén waves subjected to ponderomotive nonlinearity. Filamentation instability is known to take place for the case of dispersive Alfvén wave (DAW) propagating parallel to the ambient magnetic field. The ponderomotive force associated with DAW is responsible for wave localization and these webs of filaments become more intense and irregular as one proceeds along the spatial domain. The ponderomotive force associated with pump changes with pump parameters giving rise to different evolution patterns. This paper studies in detail the nonlinear evolution of filamentation instability introduced by dispersive Alfven waves (DAWs) which becomes dispersive on account of the finite frequency of DAW i.e., pump frequency is comparable to the ion cyclotron frequency. We have explicitly obtained the perturbation dynamics and then examined the impact of pump magnitude on the driven magnetic turbulence using numerical simulation. The results show steepening at small scales with increasing pump amplitude. The compressibility associated with acoustic fluctuations may explain the variation in spectral scaling of solar wind turbulence as observed by Alexandrova et al. (Astrophys. J. 674:1157, 2008). 相似文献
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Emission of methane and nitrous oxides from agricultural soils and related global warming potentials of Murshidabad District,West Bengal 
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下载免费PDF全文 Agricultural activities emit substantial amounts of methane (CH4) and nitrous oxides (N2O), the two important greenhouse gases (GHG) with high global warming potentials (GWP). So far, many studies have already been carried out at national and state level, but lack micro‐level (district or block‐level) inventory in India. The present study sheds light on the flux of CH4 and N2O (from all possible sources) from agricultural soil of various blocks in the Murshidabad district, based on the inventory prepared, using the IPCC methodology, with adjusted emission factors and coefficients appropriate for the local level. The economy of the Murshidabad district almost completely rests on agriculture as more than 80 per cent of the population is directly or indirectly dependent on it for their livelihood. Paddy is the dominating crop, cultivated on more than 60 per cent of the gross cropped area. The present work is based on the review of various literature and reports collected from respective state government offices and websites. Results show that CH4 and N2O emission from the agricultural fields are 126.405 Gg and 0.652 Gg respectively for the year 2011?12 with a large scale spatial variation (block‐level) within the district. 相似文献
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Sediment storage and release from Himalayan piggyback basins and implications for downstream river morphology and evolution 下载免费PDF全文
下载免费PDF全文 Alexander L. Densmore Rajiv Sinha Swati Sinha S. K. Tandon Vikrant Jain 《Basin Research》2016,28(4):446-461
Piggyback basins developed at the mountain fronts of collisional orogens can act as important, and transient, sediment stores along major river systems. It is not clear, however, how the storage and release of sediment in piggyback basins affects the sediment flux and evolution of downstream river reaches. Here, we investigate the timing and volumes of sediment storage and release in the Dehra Dun, a piggyback basin developed along the Himalayan mountain front in northwestern India. Based on OSL dating, we show evidence for three major phases of aggradation in the dun, bracketed at ca. 41–33 ka, 34–21 ka and 23–10 ka, each accompanied by progradation of sediment fans into the dun. Each of these phases was followed by backfilling and (apparently) rapid fan‐head incision, leading to abandonment of the depositional unit and a basinward shift of the active depocentre. Excavation of dun sediment after the second and third phases of aggradation produced time‐averaged sediment discharges that were ca. 1–2% of the modern suspended‐sediment discharges of the Ganga and Yamuna rivers that traverse the margins of the dun; this sediment was derived from catchment areas that together comprise 1.5% of the drainage area of these rivers. Comparison of the timing of dun storage and release with upstream and downstream records of incision and aggradation in the Ganga show that sediment storage in the dun generally coincides with periods of widespread hinterland aggradation but that late stages of dun aggradation, and especially times of dun sediment excavation, coincide with major periods of sediment export to the Ganga Basin. The dun thus acts to amplify temporal variations in hinterland sediment supply or transport capacity. This conceptual model appears to explain morphological features of other major river systems along the Himalayan front, including the Gandak and Kosi Rivers, and may be important for understanding sediment flux variations in other collisional mountain belts. 相似文献
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The impact of two boundary-layer parameterisation schemes on the prediction of Indian monsoon systems by a global spectral model has been investigated. The turbulent kinetic energy closure scheme shows a positive impact on the prediction of some important synoptic features, including the genesis of monsoon lows, the tracking of monsoon depressions, and precipitation. 相似文献
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A. N. V. Satyanarayana U. C. Mohanty N. V. Sam Swati Basu V. N. Lykossov 《Journal of Earth System Science》2000,109(2):293-303
An attempt has been made to study the marine boundary layer characteristics over Bay of Bengal using BOBMEX (Bay of Bengal
and Monsoon Experiment) pilot experiment data sets, which was conducted between 23rd October and 12th November 1998 on board
ORV Sagar Kanya. A one-dimensional multilevel atmospheric boundary layer with TKE-ε closure scheme is employed to study the
marine boundary layer characteristics. In this study two synoptic situations are chosen: one represents an active convection
case and the other a suppressed convection. In the present article the marine boundary layer characteristics such as temporal
evolution of turbulent kinetic energy, height of the boundary layer and the airsea exchange processes such as sensible and
latent heat fluxes, drag coefficient for momentum are simulated during both active and suppressed convection. Marine boundary
layer height is estimated from the vertical profiles of potential temperature using the stability criterion. The model simulations
are compared with the available observations. 相似文献
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Variation in absolute abundance, size and coiling direction ratio of the planktic foraminifera Globorotalia menardii during the late Quaternary have been studied in three cores, collected along a north-south transect from the northeastern Indian Ocean. Increased abundance and larger size is observed during the warm interglacial period, whereas, smaller and fewer G. menardii specimens are noted during the cold glacial periods. A comparatively better match between absolute abundance, size and oxygen isotopic composition of foraminifera as compared to carbon isotopic composition at all the locations indicates that the abundance and size of G. menardii is more affected by seawater temperature and salinity as compared to productivity changes. The amplitude and frequency of temporal changes in the abundance and size of G. menardii vary from core-to-core, indicating the influence of site-specific physico-chemical conditions. In comparison to the abundance and size, the coiling direction of G. menardii does not show any systematic change in any of the cores. The majority of the specimens coil sinistrally. We conclude that the absolute abundance and variation in the average size of G. menardii can be used to infer past climatic changes. However, the variation in coiling direction of G. menardii appears to be unaffected by late Quaternary paleoclimatic variations in the north-eastern Indian Ocean. 相似文献
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Drought hazard assessment using geoinformatics over parts of Chotanagpur plateau region, Jharkhand, India 总被引：4，自引：3，他引：1
Swati Pandey A. C. Pandey M. S. Nathawat Manoj Kumar N. C. Mahanti 《Natural Hazards》2012,63(2):279-303
Recurrent drought events in the Palamu district of Jharkhand state and the magnitude of drought losses primarily toward agricultural production in this dominantly monocropped region indicate the continuing susceptibility of the society to drought. This paper presents a method for spatial, geoinformatics-based assessment of agricultural, meteorological, and hydrological drought hazard in Palamu district. It was hypothesized that the key climatic, biophysical and social factors that define agricultural drought hazard were soils, geomorphology, drainage density, land use, and relief, whereas for meteorological drought hazard, it is rainfall, coefficient of variation of rainfall and for hydrological drought hazard, it is lithology, depth to water table, aquifer yield, and surface water bodies. The framework for the derivation of an agricultural, meteorological, and hydrological drought hazard map was created through the development of a numerical weighting scheme to evaluate the drought potential of the classes within each factor. A cumulative map created through spatial join of all the three types of drought provided a drought hazard scenario in totality. The area with different severity of drought hazards under cumulative drought hazards scenario (viz. very low (8.9?%), low (24.2?%), moderate (29.2?%), high (20.13), and very high (17.3?%)) revealed high drought proneness of the area and the usefulness of geoinformatics in better spatial prognosis of drought hazards. 相似文献