Application of remote sensing techniques in snow and ice hydrology

The contribution of snow and ice melt towards the water discharges of most of the Himalayan rivers is highly significant. It is, therefore, necessary to monitor the snow accumulation and depletion, and study the melting processes to help in efficient management of water resources. It is also important to compile a glacier inventory for the purpose. The snow bound areas in the Himalaya lie at high altitudes where the terrain is rugged and inaccessible. This renders the conventional methods of study not only difficult but hazardous as well. Remote sensing techniques, therefore, have a vital role to play in these studies for quick results with much less cost. Visual interpretation of Landsat imagery in Beas river basin and use of aerial photographs for glacier inventory in Baspa river basin have been cited as case studies. To perfect the methodology used in various remote sensing techniques, a pilot project approach has been suggested.     

Spherical shock waves in viscous magnetogasdynamics

The point-source, spherical magnetogasdynamics shock wave moving into a constant density -law gas is considered in the limit of infinite shock strength, from the point of view of the Richtmyer-Von Neumann viscosity technique. Numerical solutions of this problem has been obtained in viscous and non-viscous regions. A similarity solution of this problem is shown to exist. We have shown that field variables change rapidly when the magnetic field is imposed in both the viscous and the non-viscous regions.Supported by CSIR, New DeIhi under the grant No. 7157/287/81-DMR-I.     

Structural and metamorphic evolution of the rocks of the Jutogh Group, Chur half-klippe, Himachal Himalayas: A summary and comparison with the Simla area

The rocks of the Jutogh Group in the Himachal Himalayas and their equivalents elsewhere are now considered to represent a several km thick crustal scale ductile shear zone, the so called Main Central Thrust Zone. In this article we present a summary of structural and metamorphic evolution of the Jutogh Group of rocks in the Chur half-klippe and compare our results with those of Naha and Ray (1972) who worked in the adjacent Simla klippe. The deformational history of the Jutogh Group of rocks in the area around the Chur-peak, as deduced from small-scale structures, can be segmented into: (1) an early event giving rise to two sets of very tight to isoclinal and coaxial folds with gentle dip of axial planes and easterly or westerly trend of axes, (2) an event of superimposed progressive ductile shearing during which a plethora of small-scale structures have developed which includes successive generations of strongly non-cylindrical folds, several generations of mylonitic foliation, extensional structures and late-stage small-scale thrusts, and (3) a last stage deformation during which a set of open and upright folds developed, but these are regionally unimportant. The structure in the largest scale (tens of km) can be best described in terms of stacked up thin thrust sheets. Km-scale asymmetric recumbent folds with strongly non-cylindrical hinge lines, developed as a consequence of ductile shearing, are present in one of these thrust sheets. The ductile shearing, large-scale folding and thrusting can be related to the development of the Main Central Thrust Zone. The microstructural relations show that the main phase of regional low-to medium-grade metamorphism (T ≈ 430–600°C andP ≈ 4.5–8.5 kbar) is pre-kinematic with respect to the formation of the Main Central Thrust Zone. Growth zoned garnets with typical bell-shaped Mn profiles and compensating bowl-shaped Fe profiles are compatible with this phase of metamorphism. Some of the larger garnet grains, however, show flat compositional profiles; if they represent homogenization of growth zoning, it would be a possible evidence of a relict high-grade metamorphism. The ductile shearing was accompanied by a low-greenschist facies metamorphism during which mainly chlorite and occasionally biotite porphyroblasts crystallized.     

Period changes in DF Hydrae

The period study of the eclipsing binary DF Hya, based on up-to-date minima has been presented. The least-squares method has been applied to obtain a new period, which comes out to be 0 _. ^d 3306017. Period changes are found around the years 1949, 1974, and 1982. Appreciable period changes are apparent around 1949 and 1974, the strongest being around 1974. The period changes (P) range from 0.46×10^–6 d to 0.46×10^–5 d, the average being 1.89×10^–6 d. Such period changes are usual for a contact system, like DF Hya. Our results do not show increase in the time interval 1959–1985 as suggested by Zhanget al. (1989).     

Thermal convection instability of a two-component fluid layer in hydromagnetics

The thermal convection instability of a two component fluid layer subjected to a temperature gradient has been studied in the presence of an applied magnetic field. The associated thermal diffusion separation has a predominant effect even when the separations are small. Solutions for the non-oscillatory marginal states have been obtained. It is shown that the concentration gradient has a stabiliting or destabilizing effect according as T<or>0. Approximate solutions for the oscillatory solutions have been obtained by the method of variational principle and the dispersion relation has been solved numerically.     

Non-linear analysis of the stability of the Screw Pinch

Non-linear effects on the stability of the Screw Pinch in cylindrical system surrounded by a uniform pitch magnetic field in an incompressible pressureless plasma have been studied. A linear dispersion relation governing the stability of interface has been obtained with the help of normal mode analysis. Perturbation technique has been used to obtain the non-linear Schrödinger equation for the time variation of amplitudeA(t) which evolves according to . This can lead to non-linear stabilization, explosive instability or eventual decay, depending on the sign of . The whole calculations have been made form=1, kink modes in a sharp boundary plasma pinch. Non-linear analysis for -pinch (0) andz-pinch () have also been discussed in detail. It has been found that non-linear theory have a destabilizing influence on both - andz-pinches.     

Validation of ERS-1 and High-Resolution Satellite Gravity with in-situ Shipborne Gravity over the Indian Offshore Regions: Accuracies and Implications to Subsurface Modeling

Geoid and gravity anomalies derived from satellite altimetry are gradually gaining importance in marine geoscientific investigations. Keeping this in mind, we have validated ERS-1 (168 day repeat) altimeter data and very high-resolution free-air gravity data sets generated from Seasat, Geosat GM, ERS-1 and TOPEX/POSEIDON altimeters data with in-situ shipborne gravity data of both the Bay of Bengal and the Arabian Sea regions for the purpose of determining the consistencies and deviations. The RMS errors between high resolution satellite and ship gravity data vary from 2.7 to 6.0 mGal, while with ERS-1 data base the errors are as high as 16.5 mGal. We also have generated high resolution satellite gravity maps of different regions over the Indian offshore, which eventually have become much more accurate in extracting finer geological structures like 85° E Ridge, Swatch of no ground, Bombay High in comparison with ERS-1satellite-derived gravity maps. Results from the signal processing related studies over two specific profiles in the eastern and western offshore also clearly show the advantage of high resolution satellite gravity compared to the ERS-1 derived gravity with reference to ship gravity data.     

Diurnal variation of the total magnetic field along the east coast of Canada

The amplitude and phase values of the diurnal variations of the total magnetic field on the east coast of Canada were obtained from short time recordings over a four year period. The results show a decrease in amplitude and increase in phase of the variations at a station located near the continental margin relative to those at a coastal station, contrary to the expected ocean edge effect.     

Analysis of stability of earthen dams in kachchh region, Gujarat, India

The Kachchh region of Gujarat, India bore the brunt of a disastrous earthquake of magnitude M_w = 7.6 that occurred on January 26, 2001. The major cause of failure of various structures including earthen dams was noted to be the presence of liquefiable alluvium in the foundation soil. Results of back-analysis of failures of Chang, Tappar, Kaswati and Rudramata earth dams using pseudo-static limit equilibrium approach presented in this paper confirm that the presence of liquefiable layer contributed to lesser factors of safety leading to a base type of failure that was also observed in the field. Following the earthquake, earth dams have been rehabilitated by the concerned authority and it is imperative that the reconstructed sections of earth dams be reanalyzed. It is also increasingly realized that risk assessment of dams in view of the large-scale investment made and probabilistic analysis is necessary. In this study, it is demonstrated that the probabilistic approach when used in conjunction with deterministic approach helps in providing a rational solution for quantification of safety of the dam and in the estimation of risk associated with the dam construction.