Convective dynamos in spherical wedge geometry     

P.J. Kpyl  M.J. Korpi  A. Brandenburg  D. Mitra  R. Tavakol 《Astronomische Nachrichten》2010,331(1):73-81

Self‐consistent convective dynamo simulations in wedge‐shaped spherical shells are presented. Differential rotation is generated by the interaction of convection with rotation. Equatorward acceleration and dynamo action are obtained only for sufficiently rapid rotation. The angular velocity tends to be constant along cylinders. Oscillatory large‐scale fields are found to migrate in the poleward direction. Comparison with earlier simulations in full spherical shells and Cartesian domains is made (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Deep learning for predicting the monsoon over the homogeneous regions of India   总被引：1，自引：0，他引：1  

Moumita Saha  Pabitra Mitra  Ravi S Nanjundiah 《Journal of Earth System Science》2017,126(4):54

Indian monsoon varies in its nature over the geographical regions. Predicting the rainfall not just at the national level, but at the regional level is an important task. In this article, we used a deep neural network, namely, the stacked autoencoder to automatically identify climatic factors that are capable of predicting the rainfall over the homogeneous regions of India. An ensemble regression tree model is used for monsoon prediction using the identified climatic predictors. The proposed model provides forecast of the monsoon at a long lead time which supports the government to implement appropriate policies for the economic growth of the country. The monsoon of the central, north-east, north-west, and south-peninsular India regions are predicted with errors of 4.1%, 5.1%, 5.5%, and 6.4%, respectively. The identified predictors show high skill in predicting the regional monsoon having high variability. The proposed model is observed to be competitive with the state-of-the-art prediction models.  相似文献   

Assessment of heavy metal pollution in soils around a paper mill using metal fractionation and multivariate analysis     

P. Borah  A. Paul  P. Bora  P. Bhattacharyya  T. Karak  S. Mitra 《International Journal of Environmental Science and Technology》2017,14(12):2695-2708

Effects of paper mill wastes on the status of soil copper (Cu), manganese (Mn) and zinc (Zn) in and around 16 sites near a paper mill in Assam, North East India (26°07.485′ to 26°07.915′ N latitude and 92°12.706′ to 92°15.065′ E longitude), have been investigated in the present study. The six-step sequential extraction techniques revealed that the water-soluble fraction had the least contribution (below detectable limit to 3.24 mg kg^?1 of Cu, 13.87 mg kg^?1 of Mn and 1.25 mg kg^?1 of Zn) towards soil contamination, irrespective of the metals evaluated. Chemical fractionation of Cu, Mn and Zn in majority of the sampling locations showed non-homogenous orders of contamination. Comparison of the magnitude of local and individual heavy metal contamination factors against global values showed that the places near the paper mill waste disposal site displayed higher potential risk from metal contamination. Furthermore, the mobility factor related to ecotoxicity of soil environment was found to be metal specific and depended not only on total metal concentration but also on the nature of metal in the order Mn > Cu > Zn.  相似文献   

Performance testing of selected automated coastline detection techniques applied on multispectral satellite imageries     

Shreyashi Santra Mitra  D. Mitra  Abhisek Santra 《Earth Science Informatics》2017,10(3):321-330

Coastline detection has been of major interest for environmentalists and many methods have been introduced to detect coastline automatically. Remote Sensing techniques are the most promising ones to deliver a satisfactory result in this regard. In our study, the objective was to retrieve performance level of certain image processing techniques vigorously used for the purpose to delineate coastline automatically and they were tested against two images acquired almost on the same period by LISS III and LANDSAT ETM+ sensors. The algorithms used in the study are Water Index, NDVI, Complex Band Ratio, ISODATA, Thresholding, ISH Transfirmation techniques. Accuracy of the shoreline detection by classifying the image in land and water has been tried to be estimated in three ways, firstly with comparison to the visually interpreted high resolution google earth image, secondly field collected GCP data of reference points of classes and thirdly the raw image itself. But problem in temporal disparity caused the constraint doing accuracy assessment from the first two reference data and maps along the coast. As a whole although four techniques among six, show satisfactory results namely density slicing, ISODATA classification, Water Index and ISH transformation technique, in the case of LISS-III and ETM+, Water Index (with kappa value being 0.95 for LISS-III and 0.97 for ETM+) and Intensity-Hue-Saturation transformation techniques give better performance. Sensor to sensor variation might have introduced certain differences in shoreline detection in images of same season with similar tidal influence.  相似文献   

Secondary dynamical spectra of pulsars as indicators of inhomogeneities in the interstellar plasma     

E. R. Safutdinov  M. V. Popov  Ya. Gupta  D. Mitra  U. Kumar 《Astronomy Reports》2017,61(5):406-416

Observations of ten bright pulsars were obtained on the Giant Meter-wavelength Radio Telescope (GMRT, India) in order to study the effects of scattering of their radio waves by contructing and analyzing secondary dynamical spectra. The observations were conducted at 610 and 1420 MHz using a digital spectral analyzer operating in a real-time regime. The frequency resolution was 32.5 or 65.1 kHz, and the readout time was from 61.44 to 512 μs. Archival data for five pulsars at 327 MHz were also used. Procedures for normalizing the spectra and for constructing the secondary dynamical spectra were developed. Parabolic arcs were found in the secondary spectra of four pulsars (B1642-03, B1556-44, B2154+40, and B2021+51). The curvature of these arcs can be used to determine the distance to the effective scattering screen. In all cases, these screens are located relatively near the pulsars themselves.  相似文献   

Motion of Venusian clouds by the deposition of meteoroids     

Ved Mitra 《Planetary and Space Science》1975,23(3):551-555

The theory of superrotation of the Earth's atmosphere by global deposition of meteoroids recently developed by the author (Mitra, 1974) is extended after a slight refinement to explain the rotation period of Venusian clouds. A satisfactory agreement with observations is obtained.  相似文献   

Comprehensive test of different cumulus parameterization schemes for the simulation of the Indian summer monsoon     

S. Das  A. K. Mitra  G. R. Iyengar  S. Mohandas 《Meteorology and Atmospheric Physics》2001,78(3-4):227-244

Summary The global spectral model of NCMRWF at T80 horizontal resolution and 18 vertical levels has been integrated for the summer season (July) using different cumulus parameterization schemes namely, the Simplified Arakawa-Schubert scheme (SAS), the Relaxed Arakawa-Schubert Scheme (RAS), and the Kuo-type cumulus parameterization scheme (KUO). The results have been compared with mean analysis of the operational NCMRWF model (ANA) and other available observations. Results indicate that, while the global distributions of basic fields such as the wind, temperature and moisture are fairly well simulated by all the three schemes, there are many differences seen in the simulation of the typical features of the Indian summer monsoon. The strength of the Low Level Westerly Jet (LLWJ), the Cross Equatorial Flow (CEF), and the Tropical Easterly Jet (TEJ) are better simulated by RAS and SAS as compared to ANA than the KUO scheme. RAS and SAS produce strong rising motion owing to strong intensity of convection produced by these two schemes. This in turn produces stronger Hadley cell by RAS and SAS than compared to the KUO scheme. Simulation of the 200 mb velocity potential and divergent wind by RAS and SAS produced two prominent centers, one in the Bay of Bengal and another in the Western Pacific, which correspond to the intense latent heating by cumulus convection during the active monsoon phase. The velocity potential and divergent winds were weaker in KUO, than compared to RAS and SAS. The simulation of OLR is improved by RAS as compared to observations. The cold bias produced by KUO at 200 mb is reduced by RAS and is substantially improved by SAS. Study of observed and simulated rainfall indicated that RAS and SAS produced better distribution of precipitation over the Western Ghat Mountains and the Arakan coast, where deep cumulus convection is produced due to orographic forcing of the warm moist air. The KUO scheme underestimated the rainfall over these two regions, but produced slightly better distribution of rainfall over the northwest and central India, where the intensity of convection is relatively weaker. Evaluation of overall dynamics, thermal structure and rainfall indicates that in general, SAS is able to provide relatively better results compared to other two schemes. Received October 3, 2000/Revised December 5, 2000  相似文献   

Geomorphology and Petroleum Prospects of Cauvery Basin,Tamilnadu, Based on Interpretation of Indian Remote Sensing Satellite (IRS) Data     

D S Mitra  R P Agarwal 《Journal of the Indian Society of Remote Sensing》1991,19(4):263-268

Geomorphological studies of the Cauvery basin, Tamilnadu were carried out using IRS images with special emphasis on identification of zones of hydrocarbon occurrences. The basin exhibits landforms of fluvial and fluvio-marine plains. Two major trends of lineaments and 15 circular anomalies have been identified. The NW-SE trend appears to be younger and might have played an important role in migration and entrapment of hydrocarbons. Six circular anomalies are associated with known oil/gas wells. The study has identified probable zones of hydrocarbon occurrences.  相似文献   

Ptygmatic structures: an analysis and review     

S. Mitra  J. Datta 《International Journal of Earth Sciences》1978,67(3):880-895

Buckling of an isolated elastic-plastic layer embedded in a Newtonian viscous matrix has been studied and the generation of ptygmatic folding leading ultimately to clod and fragmentation at the crests as well as along the limbs has been discussed. The cause of formation of some of the uncommon ptygmatic structures has also been evaluated along with a review of the different postulates.

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Zusammenfassung Im Experiment wird die Aufwölbung einer isolierten, elastisch-plastisch Lage in einer viscosen Newton'schen Matrix simuliert. Es entstehen hierbei ptygmatische Falten, die im Endstadium sowohl in den Scheiteln als auch auf den Flanken zerscheren und zerbrechen. Es kann dabei auch die Entstehung ungewöhnlicher ptygmatischer Strukturen studiert werden.

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Résumé Le gondolement d'une couche de plastique élastique enrobée dans une matrice visqueuse newtonienne montre que la formation de plis ptygmatiques conduit finalement à des loupes et des cassures dans les charnières comme aussi le long des flancs. La cause de la formation de certaines structures ptygmatiques a été également considérée sur la base des différents postulats.

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- Newton'a. , c . .

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Evaluation of metallogenic potential of the Nuggihalli greenstone belt,South India     

Sachinath Mitra  Maibam Bidyananda 《Comptes Rendus Geoscience》2003,335(2):185-192

Chromite from the north–south-trending schist belt of Nuggihalli (southern Karnataka), belonging to the greenstone belt of South India (3.0–3.5 Ga) and crystallising at 1178 °C under oxygen fugacity of ?6.67 shows komatiitic affinity. The chemical data of the Cr-spinels when plotted in the form of the discriminant function of Johan (1979) show a remarkable follow-up of the curve A, which delineates the boundary between the ‘barren’ and ‘fertile’ (with respect to the plausible presence of sulphide phases) Cr-spinel bodies. Only a few samples plot marginally within the barren region (Fig. 1), suggesting that the chromite bands should hardly hold the possibility of becoming host of sulphide mineralisation of commercial relevance.  相似文献