Some observations from the data taken in and around Kharagpur during the onset of the monsoon, 1990     

R Pradhan  B Roy  U K De  D K Rakshit 《Journal of Earth System Science》1996,105(1):17-29

During MONTBLEX 1990, various observational platforms were operated at Kharagpur and the nearby Kalaikunda Air Base. Using the data from all the platforms, one can draw the following conclusions. The temperature and wind data obtained from various sensors have overall compatibility. Sodar wind data indicate the presence of a low level jet at around 300 m above ground. The inversion height may be evaluated from the vertical profile of the sodar back-scatter echo intensity. The sub-synoptic or synoptic scale convergence modulates the inversion height and the presence of cloud-base within the inversion height in turn modulates the sensible heat and momentum fluxes.  相似文献   

Mapping of tropical dry deciduous forest and landuse in part of Vindhyan range using satellite remote sensing     

Pant  D N  Das  K K  Roy  P S 《Journal of the Indian Society of Remote Sensing》1992,20(1):9-20

Forest vegetation of Vindhyan range located in the north of G.B. Pant Sagar (dam) has been subjected to degradation due to high biotic pressure caused by the installation of thermal power plants, coal mining, heavy cattle grazing etc. In the present study Landsat TM FCC of 1∶250,000 scale was visually analysed with respect to forest vegetation types, crown density and structure along with other landuse/land cover classes. ExceptShorea robusta (Sal) andLagerstroemia parviflora (Lendia) all forest vegetation types show higher percentage of degradation and under-stocked condition with respect to their areal extent under study. Overall classification accuracy of the forest types has been found to be 88.94%. This indicates that for obtaining reliable mapping accuracy in dry deciduous areas, satellite remote sensing data of appropriate season is essential.

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Post-collapse volcanic history of calderas on a composite volcano: an example from Roccamonfina,southern Italy     

P D Cole  J E Guest  A M Duncan  D K Chester  R Bianchi 《Bulletin of Volcanology》1992,54(4):253-266

Roccamonfina, part of the Roman Potassic Volcanic Province, is an example of a composite volcano with a complex history of caldera development. The main caldera truncates a cone constructed predominantly of this caldera may have been associated with one of the ignimbritic eruptions of the Brown Leucitic Tuff (BLT) around 385 000 yr BP. The Campagnola Tuff, the youngest ignimbrite of the BLT, however, drapes the caldera margin and must postdate at least the initial stages of collapse. During the subsequent history of the caldera there were several major explosive eruptions. The largest of these was that of the Galluccio Tuff at about 300 000 yr BP. It is likely that there was further collapse within the main caldera associated with these eruptions. It is of note that despite these subsequent major explosive eruptions later collapse occurred within the confines of the main caldera. Between eruptions caldera lakes developed producing numerous lacustrine beds within the caldera fill. Extensive phases of phreatomagmatic activity generated thick sequences of pyroclastic surge and fall deposits. Activity within the main caldera ended with the growth of a large complex of basaltic trachyandestite lava domes around 150 000 yr BP. Early in the history of Roccamonfina sector collapse on the northern flank of the volcano formed the northern caldera. One of the youngest major events on Roccamonfina occurred at the head of this northern caldera with explosive activity producing the Conca Ignimbrite and associated caldera. There is no evidence that there was any linkage in the plumbing systems that fed eruptions in the main and northern calderas.  相似文献   

Geometry and evolution of superposed folding in the Zawar lead-zinc mineralised belt,Rajasthan     

A. B. Roy 《Journal of Earth System Science》1995,104(3):349-371

The lead-zinc bearing Proterozoic rocks of Zawar, Rajasthan, show classic development of small-scale structures resulting from superposed folding and ductile shearing. The most penetrative deformation structure noted in the rocks is a schistosity (S ₁) axial planar to a phase of isoclinal folding (F ₁). The lineations which parallel the hinges ofF ₁ folds are deformed by a set of folds (F ₂) having vertical or very steep axial planes. At many places a crenulation cleavage (S ₂) has developed subparallel to the axial planes ofF ₂ folds, particularly in the psammopelitic rocks. The plunge and trend ofF ₂ folds vary widely over the area. Deformation ofF ₂ folds into hook-shaped geometry and development of another set of axial planar crenulation cleavage are the main imprints of the third generation folds (F ₃) in the region. In addition to these, there are at least two other sets of cleavage planes with corresponding folds in small scales. More common among these is a set of recumbent and reclined folds (F ₄), developed on steeply dipping early-formed planes. Kink bands and associated sharp-hinged folds represent the other set (F ₅). Two major refolded folds are recognizable in the map pattern of the Zawar mineralised belt. The larger of the two, the Main Zawar Fold (MZF), shows a broad hook-shaped geometry. The other large-scale structure is the Zawarmala fold, lying south-west of the MZF. Both the major structures show truncation of lithological units along their respective east ‘limbs’, and extreme variation in the width of formations. The MZF is primarily the result of superimposition ofF ₃ onF ₂.F ₁ folds are relatively smaller in scale and are recognizable in the quartzite unit which responded to deformation mainly by buckle shortening. Large-scale pinching-and-swelling that appears in the outcrop pattern seems to be a pre-F₂ feature. The structural evolutionary model worked out to explain the chronology of the deformational features and the large-scale out-crop pattern envisages extreme east-west shortening following formation ofF ₁ structures, resulting in the formation of tight and isoclinal antiforms (F ₂) with pinched-in synforms in between. These latter zones evolved into a number of ductile shear zones (DSZs). The east-west refolding of the large-scaleF ₂ isoclinal antiforms seems to be the consequence of a continuous deformation and resultant migration of folds along the DSZs. The main shear zone which wraps the Zawar folds followed a curved path. Because of the penetrative nature of theF ₂ movement, the early lineations which were at high angles to the later ones (as is evident in the west of Zawarmala), became subparallel to the trend ofF ₂ folding over a large part of the area. Further, the virtually coaxial nature ofF ₂ andF ₃ folds and the refolding ofF ₃ folds by a new set of N-S folds is an indication of continuous progressive deformation.  相似文献   

Paleorainfall Reconstructions from Pedogenic Magnetic Susceptibility Variations in the Chinese Loess and Paleosols   总被引：2，自引：0，他引：2  

Barbara A. Maher  Roy Thompson 《Quaternary Research》1995,44(3)

The rock magnetic properties of the Chinese loess and paleosols constitute a unique and sensitive record of East Asian paleoclimate through the Quaternary Period. Systematic variations in the concentration and grain size of the magnetic minerals in these sediments have produced systematic variations in the magnetic susceptibility signal, which can be easily and rapidly measured at many sites across the Loess Plateau. Variations in many other rock magnetic properties can be used to identify the key shifts in ferrimagnetic grain size, but magnetic susceptibility alone is sufficiently sensitive to record stadial and interstadial climate stages, as well as glaciations and interglaciations. Past changes in rainfall and monsoon activity for this region are reconstructed from the susceptibility variations. The susceptibility record is calibrated using the modern relationship between rainfall and pedogenic susceptibility on the Loess Plateau. Our rainfall reconstructions identify enhanced summer monsoonal activity in the Chinese Loess Plateau region in the early Holocene and the last interglaciation. In the presently semiarid western area of the plateau, annual precipitation in interglacial times was up to 80% higher than at present; in the more humid southern and eastern areas, values were up to 20% higher than today's levels. During the last glaciation, precipitation decreased across the entire plateau, typically by 25%. The relationship between pedogenic susceptibility, climate, and weathering age was examined over the Northern Hemisphere temperate zone and the observed positive correlation between rainfall and susceptibility indicates that climate, rather than soil age, is the predominant factor that controls pedogenic susceptibility enhancement in loess soils.  相似文献   

Application of relaxation method to upward continuation of gravity and magnetic data     

A. Roy  Mr. S. D. Burman 《Pure and Applied Geophysics》1960,45(1):40-52

Summary The method of relaxation has been applied to the upward continuation of gravity and magnetic data. The method yields results that are more accurate than those given byPeters' scheme, and has certain added advantages. In an alternative approach, the finite Fourier sine transform has been used to reduce an area relaxation to a series of line relaxations. The results, again, are very satisfactory. Only the two-dimensional problem is considered, but, with the help of a digital computor, the method is directly extensible to three-dimensional problems.Presented at the symposium on Geophysical Prospecting held by the Central Board of Geophysics at Baroda (India) between Aug. 15–17, 1959. Published by kind permission of Secretary, Central Board of Geophysics.  相似文献   

Magneto-elastic waves and disturbances in initially stressed conducting media: II     

R. G. Roy  P. R. Sengupta 《Pure and Applied Geophysics》1972,101(1):54-66

Summary The paper is concerned with the investigation of the magneto-elastic waves and disturbances in initially stressed conducting media. Firstly, (a) the steady state response to moving loads in a magneto-elastic initially stressed conducting medium under an uniaxial tension has been discussed. Secondly, (b) the Lamb's problem corresponding to a line load suddenly applied in a magneto-elastic initially stressed conducting half-space bounded by a plane under uniaxial tension has been investigated. The final results obtained in both cases are in agreement with the corresponding classical problems when the initial tension is zero and the magnetic field is absent.  相似文献   

Interpretation of vertical gravity and magnetic profiles     

R. L. Dhar  A. Roy 《Pure and Applied Geophysics》1969,73(1):25-38

Summary Methods have been developed by quantitatively interpreting gravity and magnetic data in vertical bore-holes or shafts for geological bodies that can be approximated by spheres and cylinders. Master diagrams that can be directly used by the interpreter are provided.  相似文献   

Comments on Wafer Transfers and Related Problems in Urban Areas     

Roy E. Williams 《Ground water》1968,6(6):6-10

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Mascali,Mount Etna Region Sicily: An Example of Fascist Planning During the 1928 Eruption and Its Continuing Legacy     

Chester  David K.  Duncan  Angus M.  Dibben  Christopher  Guest  John E.  Lister  Philip H. 《Natural Hazards》1999,19(1):29-46

The 1928 eruption of Etna, Sicily, although the largest such event this century, has not been studied in detail. In this paper the nature of the eruption, the destruction it caused – including the complete devastation of the town of Mascali (pre-eruption population 2,000) – and emergency responses of the authorities to it are reviewed in the context of fascist politics and planning priorities. It is contended that, although at one level the response to the 1928 eruption was successful, at another fascism merely continued and enhanced a reactive, propitiatory approach to hazard mitigation. We argue that this legacy was not successfully overcome until the middle of the nineteen eighties. Finally contemporary Italian moves towards a more proactive approach to disaster planning, both generally and in the context of Etna, are discussed.  相似文献