Effect of the presence of a conducting channel between India and Sri Lanka Island on the features of the equatorial electrojet     

Mita Rajaram  B. P. Singh  N. Nityananda  A. K. Agrawal 《Geophysical Journal International》1979,56(1):127-138

Summary. Transient geomagnetic variations like SSCs, Bays, Sq and storm-time variations show anomalously large Z amplitudes at the three permanent magnetic observatories in India under the equatorial electrojet. Our earlier studies have shown that these anomalies cannot be explained in terms of the usual coastal effect. Another unique feature of this area is the small equatorial enhancement of all magnetic fluctuations, which still remains to be completely understood. It is also noticed that Z/H ratio at Annamalainagar is very large for night-time variations but becomes insignificant for day-time fluctuations, whereas no such large difference is seen at Trivandrum, the other coastal station. All the above features have been explained here by introducing the presence of a conducting channel in the lower crust or upper mantle between India and Sri Lanka Island. The anomalies of the equatorial electrojet in the Indian region thus do not necessitate the conducting surface of the mantle to be deeper in this area as has been suggested by earlier workers. A less conducting mantle in the Indian region otherwise could be difficult to incorporate in the present theories of mantle convection when this area is known to be tectonically active. The presence of the conducting channel is further confirmed by analogue model experiments of Papamastorakis. We further observe that the equatorial electrojet does have an associated internal part in the Indian region.  相似文献   

Heat and mass transfer of an oscillatory flow with Hall current,II     

H. L. Agrawal  P. C. Ram  V. Singh 《Astrophysics and Space Science》1983,94(2):383-393

An analysis of Hall current on the combined effects of thermal and mass diffusion of an electrically conducting liquid past an infinite vertical porous plate is performed. Analytical expressions for the transient velocity, the transient temperature in the boundary layer and the skin-friction on the plate are derived. The effects of various parameters on the velocity, temperature, shearing stresses and rate of heat transfer are shown by graphs and tables.  相似文献   

Evidence of low density sub-crustal underplating beneath western continental region of India and adjacent Arabian Sea: Geodynamical considerations     

O.P. Pandey  P.K. Agrawal  J.G. Negi 《Journal of Geodynamics》1996,21(4):365-377

The known high mobility of the Indian subcontinent during the period from 80 to 53 Ma has evoked considerable interest in recent times. It appears to have played an important role in shaping the subcontinental structures of western India and the adjoining Arabian Sea. During this period, a major catastrophic event took place in the form of Deccan volcanism, which coincides with the biological mass extinction at the K-T boundary, including the death of dinosaurs. The origin of Deccan volcanism is still being debated.Geophysically, western India and its offshore regions exhibit numerous prominent anomalies which testify to the abnormal nature of the underlying crust-lithosphere. In this work, we develop a two-dimensional structural model of these areas along two long profiles extending from the eastern basin of the Arabian Sea to about 1000 km inland. The model, derived from the available gravity data in the oceanic and continental regions, is constrained by seismic and other relevant information in the area, and suggests, for the first time, the presence of an extensive low-density (2.95–3.05 g/cm³) sub-crustal underplating. Such a layer is found to occur between depths of 11 and 20 km in the eastern basin of the Arabian Sea, and betweeen 45 and 60 km in the continental region where it is sandwiched in the lower lithosphere. The low density may have been caused as a result of serpentinization or fractionation of magma by a process related in some way to the Deccan volcanic event. Substantial depletion of both oceanic and continental lithosphere is indicated. We hypothesize that the present anatomy of the deformed lithosphere of the region at the K-T boundary is the result of substantial melt generated owing to frictional heat possibly giving rise to a hot cell like condition at the base of the lithosphere, resulting from the rapid movement of the Indian subcontinent between 80 and 53 Ma.  相似文献   

Palaeoclimate,stratigraphy and prehistory in north and west Rajasthan     

D. P. Agrawal  P. S. Datta  Zahid Hussain  R. V. Krishnamurthy  V. N. Misra  S. N. Rajaguru  P. K. Thomas 《Journal of Earth System Science》1980,89(1):51-66

Quaternary formations in western Rajasthan are of fluvial, locustrinal and aeolian origins. Fossil gravel ridge of Jayal in Nagaur District is one of the earliest quaternary formations so far recorded in the region. A rich lower palaeolithic habitation-cum-workshop site has been discovered in association with the gravel ridge. Multiple evidence for climatic change in the area during the quaternary period is discussed.  相似文献   

X-Ray emission from the pleiades cluster     

P. C. Agrawal  G. R. Riegler  K. P. Singh 《Astrophysics and Space Science》1983,92(1):177-180

Detection of a new X-ray source and its identification with the Pleiades cluster is reported here. The new X-ray source has an X-ray luminosity of ～10³² ergs s^?1 in the 0.15–3.0 keV energy band. The observed X-ray emission could be explained as integrated emission from a large number of stars in the cluster.  相似文献   

High pressure-temperature studies on an olivine tholeiite and a tholeiitic picrite from the pavagarh region,Gujarat, India     

Snehmani Agrawal  M M Bindal  Alok K Gupta 《Journal of Earth System Science》1990,99(1):91-98

Experimental studies have been performed on an olivine tholeiite and tholeiitic picrite at pressure and temperature ranges of 20–40 kb and 1200–1300°C. The lower and upper limits of basalt-eclogite transition zone for tholeiitic picrite are 23 kb and 31·67 kb at 1200°C, and 24·67 kb and 33·67 kb at 1300°C, whereas for olivine tholeiite, these are 27 kb and 32·33 kb at 1200°C, and 28·70 kb and 33·70 kb at 1300°C. While the assemblages for both samples below the transition region are Pl+Px+Mt, they are Pl+Gt+Px+Mt within it. The eclogite field has Gt+Px+Mt. The ratio of garnet to plagioclase increases from the transition zone to the eclogite field and with the disappearance of plagioclase, the percentage of garnet increases to 30 in the eclogite field. Comparison of our results with previous studies on basalt-eclogite transition shows that the transition zone found by us occurs at higher pressure-temperature conditions. Seismic studies of the region below the Deccan Traps show an increase in velocity (1–4%) at depth. It is suggested that after partial melting, during ascent of the basaltic liquid, a significant portion of it crystallizes within the upper mantle as pockets of eclogite. As eclogite is more dense than peridotite, their presence should cause a similar increase in the seismic velocity below the Deccan area.  相似文献   

Earthquake protection,by Andrew Coburn and Robin Spence,Wiley, Chichester,U.K. No. of pages: 355. Price: £34·95. ISBN: 0471 918334     

Ramesh Chandra Agrawal 《地震工程与结构动力学》1994,23(3):343-343

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Vertical component MAGSAT anomalies and Indian tectonic boundaries     

J G Negi  P K Agrawal  N K Thakur 《Journal of Earth System Science》1985,94(1):35-41

MAGSAT vertical component (Z-component) of crustal anomalies are correlated for the first time with major geological and tectonic boundaries/features of the Indian subcontinent. A prominent ‘low’ is consistently observed on all the profiles centred between 19° and 23° latitudes over the broad Peninsular ‘high’. The other conspicuous ‘low’ indicated from the present work is confined to the region above Sarda depression (29° N to 31° N) in the foothills of Himalayas. Interesting magnetic signatures are identified over the Narmada-Son rift and Godavari graben.  相似文献   

Impact of LULC change on the runoff,base flow and evapotranspiration dynamics in eastern Indian river basins during 1985–2005 using variable infiltration capacity approach     

Pulakesh Das  Mukunda Dev Behera  Nitesh Patidar  Bhabagrahi Sahoo  Poonam Tripathi  Priti Ranjan Behera  S K Srivastava  Partha Sarathi Roy  Praveen Thakur  S P Agrawal  Y V N Krishnamurthy 《Journal of Earth System Science》2018,127(2):19

As a catchment phenomenon, land use and land cover change (LULCC) has a great role in influencing the hydrological cycle. In this study, decadal LULC maps of 1985, 1995, 2005 and predicted-2025 of the Subarnarekha, Brahmani, Baitarani, Mahanadi and Nagavali River basins of eastern India were analyzed in the framework of the variable infiltration capacity (VIC) macro scale hydrologic model to estimate their relative consequences. The model simulation showed a decrease in ET with 0.0276% during 1985–1995, but a slight increase with 0.0097% during 1995–2005. Conversely, runoff and base flow showed an overall increasing trend with 0.0319 and 0.0041% respectively during 1985–1995. In response to the predicted LULC in 2025, the VIC model simulation estimated reduction of ET with 0.0851% with an increase of runoff by 0.051%. Among the vegetation parameters, leaf area index (LAI) emerged as the most sensitive one to alter the simulated water balance. LULC alterations via deforestation, urbanization, cropland expansions led to reduced canopy cover for interception and transpiration that in turn contributed to overall decrease in ET and increase in runoff and base flow. This study reiterates changes in the hydrology due to LULCC, thereby providing useful inputs for integrated water resources management in the principle of sustained ecology.  相似文献   

Stable (δ13C and δ15N) isotopes and magnetic susceptibility record of late Holocene climate change from a lake profile of the northeast Himalaya     

Shailesh Agrawal  Pradeep Srivastava  Sonam  N. K. Meena  Santosh K. Rai  R. Bhushan  D. K. Misra  A. K. Gupta 《Journal of the Geological Society of India》2015,86(6):696-705

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