Nonlinear kinetic energy interactions and their contributions to the growth and decay of atmospheric waves in the lower troposphere during summer monsoon, 1979     

D. R. Chakraborty  S. K. Mishra 《Meteorology and Atmospheric Physics》1997,64(3-4):215-230

Summary Lower tropospheric (1000–500) hPa kinetic energy (KE), temporal variations of KE and nonlinear KE transfer of rotational and divergent flows and energy conversion between them, partitioning further into stationary and transient components in the Fourier spectral domain and the mechanism for the evolution of significant transient waves for the month July 1979 in the latitudinal belt 10° S–30° N are studied.Divergent zonal and eddy KE show their maxima at the lowest level 1000 hPa. Lower tropospheric monsoon motion provides a non-divergent level close to 850 hPa. The daily flow patterns bear little resemblence to the climatology over tropics at 500 hPa. Although the transient mode of synoptic scale waves is stronger than that of planetary scale waves they are comparable. Analysis of energetics over global tropics can get signature of transient activities embedded in the large scale system. Summer momentum flux in the lower troposphere is essentially associated with stationary planetary and transient synoptic scale waves. Waves 1, 3 and 6 are the most preferred transient waves. Divergent to rotational KE conversion is the most dominating mechanism for the maintenance of planetary and synoptic scale waves. All categories of waves contribute towards the maintenance of zonal flows. The primary source of energy for transient synoptic scale waves is the transient divergent rotational KE transfer whereas the interaction between zonal stationary and transient wave is likely to be secondary source. Transient KE and all transient interactions, stationary KE and all stationary interactions are found to be strongest at 500 hPa and 850 hPa respectively. Growth and decay of transient waves 1 and 3 are mainly controlled by divergent-rotational KE conversions whereas those of transient wave 6 are controlled by KE transfer due to zonal-wave interaction.With 13 Figures  相似文献   

Comparative performance of per-pixel classifiers using ers-1 sar data for classification of rice crop     

M Chakraborty  S Panigrahy 《Journal of the Indian Society of Remote Sensing》1997,25(3):155-161

Three-date ERS-1 SAR data acquired on August 24, September 28 and November 2, 1995, was used to classify rice crop in a predominant rice growing region of West Bengal. India, Artificial neural network, maximum likelihood, decision rute and K-Means clustering classifiers were used. Classification accuracy was evaluated from the error matrix of same set of training and validating pixels. Rice classification accuracy improved significantly using neural network classifier. The decision rule based classifier performed equally good for most of the sites, indicating the feasibility of deriving a common rule based algorithm for large area application. Law aecuracy was observed for maximum likelihood classifier.  相似文献   

On disturbances produced in an elastic medium by twists applied on the inner surface of a spherical cavity     

S. K. Chakraborty 《Pure and Applied Geophysics》1956,33(1):17-22

Summary In this note, disturbances generated in an isotropic elastic medium by some simple types of twisting forces applied on the inner surface of a spherical cavity have been investigated. Prof.S. K. Chakraborty, Surendranath College, 24 Harrison Road,Calcutta (India).  相似文献   

An Efficient Accurate Direct Solution of Poisson’s Equation for Computation of Meteorological Parameters     

D. R. Chakraborty  P.S. Salvekar 《大气科学进展》1989,6(4):501-508

Poisson's equation is solved numerically by two direct methods, viz. Block Cyclic Reduction (BCR) method and Fourier Method. Qualitative and quantitative comparison between the numerical solutions obtained by two methods indicates that BCR method is superior to Fourier method in terms of speed and accuracy. Therefore. BCR method is applied to solve (?)2(?)= ζ and (?)2X= D from observed vorticity and divergent values. Thereafter the rotational and divergent components of the horizontal monsoon wind in the lower troposphere are reconstructed and are com pared with the results obtained by Successive Over-Relaxation (SOR) method as this indirect method is generally in more use for obtaining the streamfunction ((?)) and velocity potential (X) fields in NWP models. It is found that the results of BCR method are more reliable than SOR method.  相似文献   

Factors affecting the performance of family planning workers: importance of geographical information systems in empirical analysis     

Ali M  De Francisco A  Khan MM  Chakraborty J  Myaux J 《International journal of population geography : IJPG》1999,5(1):19-29

Substantial variation in contraceptive prevalence rates (CPRs) and fertility rates (FRs) between community health workers (CHWs) has been documented since the inception of the Matlab family planning program in rural Bangladesh. The coefficients of variation of these indicators for Matlab CHWs were 7% and 26%, respectively, in 1995. To identify the reasons for these performance variations, geographical information system (GIS) approaches were applied to longitudinal and cross-sectional data on 80 CHWs for the period 1980-95. Each observation in the data-set included catchment area-specific characteristics, measures of CHW efficiency in service delivery, and CHW-specific characteristics for one specific year. A one-unit increase in the average age of target women in the catchment area increases the CPR by 9.2%. The CPR increases by 0.2% for each 1% increase in women's literacy and decreases by 0.1% for each 1% increase in the number of Muslim households in the catchment area. An increase of 1 sq. km in the size of the catchment area reduces the CPR by 3%. CHW performance increases with age up to 45 years and then decreases. Similarly, a 1-year increase in the average age of target women reduces the FR by 2%. A 10% increase in the size of the catchment area reduces program performance by increasing the FR by 1.4%. A single geographic barrier to movement increases the FR by 1%. This analysis indicates that CHW performance can be improved significantly by defining catchment areas through use of GIS techniques. Without knowledge of the spatial distribution of population and the physical barriers to movement, allocating a fixed number of clients per CHW may not be the most efficient approach.  相似文献   

Thermo-elastic Rayleigh waves in transversely isotropic solids     

S. K. Chakraborty  R. P. Pal 《Pure and Applied Geophysics》1969,76(1):79-86

Summary The frequency equation of the thermo-elastic Rayleigh waves in a semi-infinite transversely isotropic solid has been obtained. The form of the frequency equation for small values of the reduced frequency has also been deduced, and it is found that, as in the isotropic medium, the velocity does not depend on the frequency. But unlike the isotropic case, the velocity depends upon the thermal constants as well.  相似文献   

Regional metamorphism of pelitic rocks around Kandra,Singhbhum, Bihar     

K. R. Chakraborty  S. K. Sen 《Contributions to Mineralogy and Petrology》1967,16(3):210-232

A suite of pelitic rocks around Kandra, Singhbhum District, Bihar, displays a metamorphic gradient registered by the index minerals chlorite, biotite, garnet, staurolite and sillimanite in a Barrovian sequence. Metamorphism was by and large coeval with folding movements, and correlating the internal fabric of minerals and deformational characters, a regular sequence of the index minerals is derived. It is argued that the chronological order by itself is not sufficient to prove that metamorphism was progressive in time.Among the index minerals, garnet appears to have formed by the reaction chlorite+biotite_a+quartz garnet+biotite_b+H₂O. For the origin of sillimanite, a new reaction, 3 staurolite+muscovite+quartz=7 sillimanite+biotite+3H₂O, is suggested on the basis of significant textural features. Textural and petrological indications regarding the formation of staurolite are in discordance. Staurolite was either derived from the biotite zone phases, or should be taken to have formed, against textural evidences, from chloritoids of the garnet zone.Graphical analysis of the assemblages by Thompson's AFM projection reveals that chlorite and staurolite are excess phases owing to retrogression and incomplete reaction. Shifting of apices of triangular fields and intersection of garnet-biotite tie lines within a zone can be satisfactorily explained in terms of extra components CaO and MnO or their ratios. It is pointed out that if MgO/(MgO + FeO) between two phases show a linear relation, their tie lines will be concurrent on the AF side of the projection, the point of concurrence reflecting equilibrium and temperature of recrystallisation.  相似文献   

An analytic study on the horizontal motion of monsoon depressions     

S. K. Mishra  D. R. Chakraborty  S. S. Desai 《Meteorology and Atmospheric Physics》1983,32(1-2):35-53

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Geological features and origin of the chromite deposits of sukinda valley,Orissa, India   总被引：1，自引：0，他引：1  

K. L. Chakraborty  T. L. Chakraborty 《Mineralium Deposita》1984,19(4):256-265

The chromiferous ultramafic rocks of Sukinda Valley (21°0'–21°5'N:85°43'–86°0'E) of Orissa are intrusive into the Iron-Ore Supergroup (2,950–3,200 Ma) at the eastern periphery of the Indian Precambrian shield. Both laterally and vertically, chromite occurs as persistent layers, lenses or pockets in the serpentinized and silicified dunite-peridotite extending over a strike length of 25 km. The ultramafic rocks and the chromitite layers are cofolded with the Iron-Ore Supergroup into a plunging syncline. Primary layering, ball and pillow structures, cross laminations, graded bedding etc. can also be detected. The different varieties of chromite ore present in the area are massive, banded and spotted, laminated and friable. The grain size of chromite varies between 0.25 and 4 mm, and the fineness of the grain increases from the bottom to the top layers. The cell dimension of chromite (8.23–8.32 Å) decreases with the increase of Al₂O₃.Cr₂O₃ in pure chromite varies between 48 to 61 wt. percent, Al₂O₃ is 7.10–15.09 wt. percent, whereas Fe₂O₃ is very low (0.03–3.20 wt. percent). The amount of RO to R₂O₃ varies within a narrow limit of 0.98–1.13, indicating that the chromite is chemically balanced. The FeO to MgO ratio is intermediate between the stratiform and alpine type. Fe³⁺ and Al³⁺ increase with respect to Cr³⁺ and Mg²⁺ in the upper chromitite layers. TiO₂ lacks significant correlation with the major element composition of chromite.It is concluded that the Sukinda Valley chromitites of Orissa are predominantly stratiform in nature and were presumably formed in situ by crystal settling, the layering having been accentuated by the fluctuation of FO₂. The geological features suggest a single magmatic cycle.  相似文献   

Some characters of the bedded chromite deposits of Kalrangi,Cuttack district,Orissa, India     

K. L. Chakraborty 《Mineralium Deposita》1973,8(1):73-80

Mineralogy, size distribution of grains, and variation in chemical composition of chromitite occurring in four successive layers in serpentinite, near Kalrangi (85°45 E:21°0 N), Cuttack district, Orissa, have been studied to decipher the mode of formation of the ore bodies. The parent rocks are dunite-peridotite with olivine, olivine-enstatite and minor chromite, the minerals being completely altered to serpentine or talc-serpentine near the surface. The ore bodies are of bedded nature, composed entirely of chromite, and are confined to the top of the dunite-peridotite sheet. Grain-size variation of chromite in different layers in the vertical section shows straight line character which suggests accumulation of chromite grains by the process of magmatic sedimentation. The normal distribution of size variation of the chromite grains probably means that they are the products of a single magmatic cycle. Cr₂O₃ and MgO in chromitite decrease and FeO and Al₂O₃ increase in the vertical direction, which is expected when chromite crystallize from an ultrabasic magma in an undisturbed condition. Ideas of repeated injection and convection currents are negated by the absence of rhythmic layering and cyclic repetition of ultrabasics and chromite.

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Zusammenfassung Die Mineralogie, die Korngrößenverteilung und die Variation der chemischen Zusammensetzung der Chromititvorkommen in vier übereinanderliegenden Lagen im Serpentinit bei Kalrangi (85°45 E:21°0 N), Cuttack District, Orissa, wurden untersucht, um die Bildung der Erze zu verstehen. Die Muttergesteine sind Dunit-Peridotit mit Olivin, Olivin-Enstatit und wenig Chromit, wobei die Mineralien an der Oberfläche vollständig zu Serpentin oder Talk-Serpentinit verändert sind. Die Erzkörper sind geschichtet, bestehen fast völlig aus Chromit und sind auf den obersten Teil der Dunit-Peridotit-Platte beschränkt, die im Hangenden von präkambrischen Mahagiri-Quarziten einer itabiritischen Serie intrudiert ist. Die Korngrößenverteilung im Chromit in den verschiedenen Lagern des Profils zeigt geradlinigen Charakter, was auf die Anlagerung der Chromitkörner durch magmatische Sedimentation hinweist. Die lognormale Korngrößen-Häufigkeits-Verteilung der Chromitkörner spricht für einen einmaligen magmatischen Zyklus. Während Cr₂O₃ und MgO in den Chromititen systematisch nach oben abnehmen, nehmen FeO und Al₂O₃ zu, was zu erwarten ist, wenn die Chromitausscheidung in ungestörtem, ultramafischem Magma vor sich geht. Vorstellungen von wiederholten Injektionen und Konvektionsströmen sind zu widerlegen durch das Fehlen von rhythmischen Schichten und von zyklischen Wiederholungen der ultramafischen Gesteine und des Chromits.

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