Field-aligned currents and auroral acceleration by non-linear MHD waves     

M. S. Tiwari  G. Rostoker 《Planetary and Space Science》1984,32(12):1497-1503

This paper examines the consequences of the assumption that substorm-associated growth of magnetosphere-ionosphere current systems is triggered by the incidence, on the ionosphere, of a large amplitude Alfvén wave generated in the distant magnetotail. It is pointed out that there is a large body of evidence suggesting that, in the acceleration region near 1 R_E, one is likely to find a major discontinuity in mass density. Following the approach of Cohen and Kulsrud (1974) who studied the steepening of large amplitude hydromagnetic waves into shocks, we demonstrate that the character of the background plasma and magnetic field in the auroral acceleration region near 1 R_E can be ideal for the generation of MHD shocks and that these shocks can lead to the acceleration of ions and electrons as reported by investigators using S3-3 satellite data.  相似文献   

Vegetation cover classification in Sariska National Park and surroundings   总被引：2，自引：0，他引：2  

A. K. Tiwari  M. Kudrat  S. K. Bhan 《Journal of the Indian Society of Remote Sensing》1990,18(3):43-51

Appraisal of spatial distribution of vegetation types is an important aspect for wildlife habitat suitability and ecological studies. Remote sensing provides quick, accurate and cost and time effective methods for vegetation cover mapping. In the present study Landsat MSS data was digitally classified into various land use/forest type classes. Forested land was about 52 per cent of the study area. Four forest types, namelyAnogeissus pendula, Boswellia serra ta, mixedAnogeissus-Butea and mixed Acacia-Zizyphus occupied 28.47 percent, 6.60 percent, 18.60 percent and 9.70 percent of the forested land, respectively. The area under National Park was 51.28 percent of total study area. About 61 percent of the Park area was under tree-covered vegetation. Overall accuracies for classified and smoothened-classified images were 89.37 percent and 91.96 percent, respectively. The vegetation of the area is controlled by topography and edaphic factors.  相似文献   

Radiative effects of black carbon aerosols on Indian monsoon: a study using WRF-Chem model     

Pramod?SoniEmail author  Sachchida?Nand?Tripathi  Rajesh?Srivastava 《Theoretical and Applied Climatology》2018,132(1-2):115-134

The Weather Research and Forecasting model with Chemistry (WRF-Chem) is utilized to examine the radiative effects of black carbon (BC) aerosols on the Indian monsoon, for the year 2010. Five ensemble simulations with different initial conditions (1st to 5th December, 2009) were performed and simulation results between 1st January, 2010 to 31st December, 2010 were used for analysis. Most of the BC which stays near the surface during the pre-monsoon season gets transported to higher altitudes with the northward migration of the Inter Tropical Convergence Zone (ITCZ) during the monsoon season. In both the seasons, strong negative SW anomalies are present at the surface along with positive anomalies in the atmosphere, which results in the surface cooling and lower tropospheric heating, respectively. During the pre-monsoon season, lower troposphere heating causes increased convection and enhanced meridional wind circulation, bringing moist air from Indian Ocean and Bay of Bengal to the North-East India, leading to increased rainfall there. However, during the monsoon season, along with cooling over the land regions, a warming over the Bay of Bengal is simulated. This differential heating results in an increased westerly moisture flux anomaly over central India, leading to increased rainfall over northern parts of India but decreased rainfall over southern parts. Decreased rainfall over southern India is also substantiated by the presence of increased evaporation over Bay of Bengal and decrease over land regions.  相似文献   

1891–1883 Ma Southern Bastar–Cuddapah mafic igneous events, India: A newly recognized large igneous province     

Jason E. French  Larry M. Heaman  Thomas Chacko  Rajesh K. Srivastava 《Precambrian Research》2008,160(3-4):308-322

A newly recognized remnant of a Paleoproterozoic Large Igneous Province has been identified in the southern Bastar craton and nearby Cuddapah basin from the adjacent Dharwar craton, India. High precision U–Pb dates of 1891.1 ± 0.9 Ma (baddeleyite) and 1883.0 ± 1.4 Ma (baddeleyite and zircon) for two SE-trending mafic dykes from the BD2 dyke swarm, southern Bastar craton, and 1885.4 ± 3.1 Ma (baddeleyite) for a mafic sill from the Cuddapah basin, indicate the existence of 1891–1883 Ma mafic magmatism that spans an area of at least 90,000 km² in the south Indian shield.This record of 1.9 Ga mafic/ultramafic magmatism associated with concomitant intracontinental rifting and basin development preserved along much of the south-eastern margin of the south Indian shield is a widespread geologic phenomenon on Earth. Similar periods of intraplate mafic/ultramafic magmatism occur along the margin of the Superior craton in North America (1.88 Ga Molson large igneous province) and in southern Africa along the northern margin of the Kaapvaal craton (1.88–1.87 Ga dolerite sills intruding the Waterberg Group). Existing paleomagnetic data for the Molson and Waterberg 1.88 Ga large igneous provinces indicate that the Superior and Kalahari cratons were at similar paleolatitudes at 1.88 Ga but a paleocontinental reconstruction at this time involving these cratons is impeded by the lack of a robust geological pin such as a Limpopo-like 2.0 Ga deformation zone in the Superior Province. The widespread occurrence of 1.88 Ga intraplate and plate margin mafic magmatism and basin development in numerous Archean cratons worldwide likely reflects a period of global-scale mantle upwelling or enhanced mantle plume activity at this time.  相似文献   

Petrology, geochemistry and genesis of rift-related carbonatites of Ambadungar, India     

Rajesh K. Srivastava 《Mineralogy and Petrology》1997,61(1-4):47-66

Summary The Ambadungar (Amba Dongar) alkaline carbonatite complex is emplaced in the Deccan traps igneous province. A wide range of carbonatites and alkaline rocks are exposed around Ambadungar. The alkaline rocks have been classified as tinguaite, phonolite and/or phononephelinite, melanephelinite, and syenite and/or nepheline syenite whereas carbonatites vary from calcio-carbonatites to ferro- and silicocarbonatites. The enrichment in large-ion lithophile elements (LILE), P, and rare-earth elements (REE) in carbonatites is considered to result from fractionation of a mantle derived magmatic liquid, i.e. nephelinitic magma, by liquid immiscibility which also produced melanephelinite and/or phononephelinite with high field strength elements (HFSE) such as Ca, Mg, Fe, and Mn in the alkaline silicate liquid fraction. The La:Lu ratios of the carbonatites are typical of igneous rocks and vary between 590 and 1945, similar to many known magmatic carbonatites. The ¹³C concentration varies between –2 and –8 whereas ¹⁸O-values vary between 7.7 and 26.8. The ¹³C concentration is typical of primary igneous carbonatites but ¹⁸O enrichment is thought to be the result of post-magmatic processes such as interaction with meteoric water and re-equilibration with hydrous fluids at low temperatures.

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Petrologie, Geochemie und Genese der riftgebundenen Karbonatite von Ambadungar, Indien

Zusammenfassung Der Ambadungar (Amba Dongar) Alkalikarbonatit-Komplex liegt in der magmatischen Deccan Provinz. Er umfaßt eine Vielzahl von karbonatitischen und alkalischen Gesteinen, die in der Umgebung von Ambadungar aufgeschlossen sind. Die Alkaligesteine sind als Tinguaite, Phonolite und/oder Phononephelinite, Melanephelinite, Syenite und/oder Nephelinsyenite zu klassifizieren, die Karbonatite als Calcio-, bis Ferro- and Silicokarbonatite. Die Anreicherung an LIL-Elementen und Seltenen Erden in den Karbonatiten werden als das Ergebnis der Fraktionierung von Mantelschmelzen, i.e. eines nephelinitisches Magmas, infolge von Nichtmischbarkeit interpretiert. Melanephelinite und/oder Phononephelinite and hohe Gehalte an HFS-Elementen (Ca, Mg, Fe and Mn) in der alkalisch-silikatischen Schmelzfraktion sind ebenfalls das Ergebnis dieser Prozesse. Die La/Lu-Verhältnisse sind typisch für magmatische Karbonatite and variieren zwischen 590 and 1945. Die ¹³C Konzentrationen variieren zwischen -2 and -8 %o, die ¹⁸O Werte zwischen 7.7 and 26.8 %0. Während die ¹³C Konzentration typisch für primär magmatische Karbonatite ist, ist die ¹⁸O-Anreicherung mit postmagmatischen Prozessen, wie etwa die Interaktion mit meteorischen Wässern and die Reequilibration mit niedrig temperierten wäßrigen Fluiden, erklärbar.

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with 11 figures  相似文献   

Hydrogeochemical investigation and qualitative assessment of surface water resources in West Bokaro coalfield,India     

Ashwani Kumar Tiwari  Prasoon Kumar Singh  Mukesh Kumar Mahato 《Journal of the Geological Society of India》2016,87(1):85-96

A hydrogeochemical study of surface water of the West Bokaro coalfield has been undertaken to assess its quality and suitability for drinking, domestic and irrigation purposes. For this purpose, fourteen samples collected from rivers and ponds of the coalfield were analysed for pH, conductivity, total dissolved solids (TDS), major cations (Ca²⁺, Mg²⁺, Na⁺ and K⁺), major anions (HCO₃^-, F^-, Cl^-, SO₄^2- and NO₃^-) and trace metals. The pH of the analysed water samples varied from 7.3 to 8.2, indicating slightly alkaline in nature. The electrical conductivity (EC) value varied from 93 μs cm^-1 to 906 μs cm^-1 while the TDS varied from 76 mg L^-1 to 658 mg L^-1. HCO₃^- and SO₄^2- are the dominant anion and Ca²⁺ and Na⁺ the cation in the surface water. The concentration of alkaline earth metals (Ca²⁺ + Mg²⁺) exceed the alkali metals (Na⁺ + K⁺) and HCO₃^- dominates over SO₄^2- + Cl^- concentrations in the majority of the surface water samples. Ca²⁺ -Mg²⁺ -HCO₃^- and Ca²⁺ -Mg²⁺ -Cl^- are the dominant hydrogeochemical facies in the surface water of the area. The water chemistry is mainly controlled by rock weathering with secondary contribution from anthropogenic sources. For quality assessment, analyzed water parameter values compared with Indian and WHO water quality standard. In majority of the samples, the analyzed parameters are well within the desirable limits and water is potable for drinking purposes. However, concentrations of TDS, TH, Ca²⁺, Mg²⁺ and Fe are exceeding the desirable limits in some water samples and needs treatment before its utilization. The calculated parameters such as sodium absorption ration, percent sodium, residual sodium carbonate, permeability index and magnesium hazard revealed good to permissible quality and suitable for irrigation purposes, however, higher salinity, permeability index and Mg-ratio restrict its suitability for irrigation at few sites.  相似文献   

Sargipali galenas: Unusual lead-isotope data from eastern India     

Rajesh K. Vishwakarma  A. V. Ulabhaje 《Mineralium Deposita》1991,26(1):26-29

The Sargipali sulphide deposit, hosted by a sequence of metasediments of the Precambrian Gangpur Series, represents the stratiform and stratabound Pb-Cu mineralization. Lead-isotope analyses obtained from six galena samples of different forms and stratigraphical levels, yielded a model Pb age of 1665 Ma, which predates the episodes of deformation and metamorphism ( 850 Ma) as well as syn-to late-tectonic magmatism. The model Pb age, on the contrary, shows a relationship to the closing phase of the Gangpur sedimentation (1700 Ma) in a shallow-water marine environment. The notable paucity of the interlayered volcanic rock in the deposit and its Pb-rich nature possibly point to its being the sedimentary exhalative (SEDEX) type. Documentary evidence for the Pb component from the geological environment of the upper continental crust is revealed by an exceptionally high (= ²³⁸U/²⁰⁴Pb) and the slightly above average W(= ²³²Th/²³⁸U) values. These indicate that the source rock was initially rich in U-Th-Pb concentration. For the Sargipali ore Pb, the parent is assumed to be late Archean-lower Proterozoic soda granite.  相似文献   

Study of Cosmic-Ray Intensity Variations Associated with Anomalous,Long-Duration High-Speed Solar Wind Streams in 2003     

Laxmi Tripathi  Anil Kumar Tiwari  S. P. Agrawal 《Solar physics》2007,241(1):171-184

High-speed solar wind streams (HSWS) were identified for solar cycles 22 and 23 (up to 2004). Preliminarily, HSWS were classified in three groups according to their continuous period of occurrence. In the declining phase of solar cycle 23, 2003 is found to be anomalous, showing a very large number of HSWS events of long duration (> ten days). We have studied the effect of HSWS on the cosmic-ray intensity as well as their relationship with geomagnetic disturbance index Ap on yearly, daily, and hourly bases. The yearly average of solar-wind speed was also found to be maximum in 2003. Being within the declining phase of solar activity, the occurrence of solar flares in 2003 is quite low. In particular during HSWS, no solar flares have been observed. Associations with cosmic-ray changes do not support the notion that the HSWS are usually effective in producing significant cosmic-ray decreases. Out of 12 HSWS events observed during the period 2002 (December) to 2003, four events of significant cosmic-ray decreases at all the stations have been selected for further analysis. The cosmic-ray intensity has been found to decrease during the first phase of the event (first five days of HSWS) at all three neutron-monitor stations situated at different latitudes with different cutoff rigidities. The rigidity spectra of observed decreases in cosmic-ray intensity for these four cases have been found to be significantly different than that of Fds (Forbush decrease). In two cases the spectra are softer, whereas in the other two they are harder than that of Fds. However, if the average of all four events is considered together then the spectra of the decrease in cosmic rays during HSWS exactly match that of Fds. Such a result implies that initially individual events should be considered, instead of combining them together, as was done earlier. The Ap index is also found to generally increase in the first phase of the event. However, the four events selected on the basis of cosmic-ray decrease are not always associated with enhanced values of the Ap index. As such, the significance of our study is that further detailed investigations for much longer periods and on an event-by-event basis is required to understand the effect of coronal-hole-associated HSWS.  相似文献   

Effect of general loss-cone distribution function on electrostatic ion-cyclotron instability in an inhomogeneous plasma: particle aspect analysis     

Ruchi Mishra  M. S. Tiwari 《Earth, Moon, and Planets》2007,100(3-4):195-214

The electrostatic ion-cyclotron instability (EICI) in low β (ratio of plasma to magnetic pressure), anisotropic, inhomogeneous plasma is studied by investigating the trajectories of the particles using the general loss-cone distribution function (Dory-Guest-Harris type) for the plasma ions. In particular, the role of the loss-cone feature as determined by the loss-cone indices, in driving the drift-cyclotron loss-cone (DCLC) instability is analysed. It is found that for both long and short wavelength DCLC mode the loss-cone indices and the perpendicular thermal velocity affect the dispersion equation and the growth rate of the wave by virtue of their occurrence in the temperature anisotropy. The dispersion relation for the DCLC mode derived here using the particle aspect analysis approach and the general loss-cone distribution function considers the ion diamagnetic drift and also includes the effects of the parallel propagation and the ion temperature anisotropy. It is also found that the diamagnetic drift velocity due to the density gradient of the plasma ions in the presence of the general loss-cone distribution acts as a source of free energy for the wave and leads to the generation of the DCLC instability with enhanced growth rate. The particle aspect analysis approach used to study the EICI in inhomogeneous plasma gives a fairly good explanation for the particle energisation, wave emission by the wave–particle interaction and the results obtained using this particle aspect analysis approach are in agreement with the previous theoretical findings using the kinetic approach.  相似文献   

Simultaneous measurements of black carbon and PM2.5, CO,and NO x variability at a locally polluted urban location in India     

S. Tiwari  D. S. Bisht  A. K. Srivastava  Örjan Gustafsson 《Natural Hazards》2015,75(1):813-829

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