Inductive electric fields in the magnetosphere     

M. Roy  Ramaswamy Rajaram 《Planetary and Space Science》1979,27(6):817-819

A quantitative estimate of the electric fields induced by the time dependent ring current is made incorporating the drifts and induced electric fields in a self-consistent manner. It has been shown that in the ring current region, the results of the self-consistent calculations deviate substantially from the first order estimates hitherto obtained. Since for a rapidly varying ring current, the induced electric field can be of the same order as the convection electric field in the magnetosphere, these deviations have to be taken into account in substorm studies.  相似文献   

Study of Aeromagnetic Data Over Part of Eastern Ghat Mobile Belt and Bastar Craton     

S.P. Anand  Mita Rajaram   《Gondwana Research》2003,6(4):859-865

A portion of the aeromagnetic anomaly map of India, from 17⁰ to 20⁰ N and 78^o to 84^o E has been analysed to understand the tectonics of the region. The distribution of magnetic sources in the study region are clearly brought out in the analytic signal map and found to be associated with charnockitic rocks, iron formation and trap flows. The Godavari Graben is devoid of any magnetic sources. High-grade charnockitic rocks on surface and sub-surface, flank the shoulders of the Godavari Graben on either side. From the analysis of magnetic data, Sileru Shear Zone (SSZ) is identified as the contact of the Bastar craton and the Eastern Ghat Mobile Belt (EGMB). The Eastern Ghat is divided into two blocks: Block-N north of Srikakulam is devoid of magnetic sources while the charnockitic rocks are the main magnetic carriers in Block-S. The difference in magnetic characteristics of the two blocks has been attributed to the difference in metamorphic history. Block-N has an over print of amphibolite facies metamorphism while Block-S to the south depicts granulite facies metamorphism. The Euler solutions within the EGMB shows that the magnetic sources along SSZ is shallower than the south east implying that the exhumation process in the EGMB has a differential rate.  相似文献   

Obituary     

Mita Rajaram 《Journal of the Geological Society of India》2018,92(6):770-770

  相似文献   

SporadicE ionization associated with meteor events     

Girija Rajaram  H Chandra 《Journal of Earth System Science》1991,100(3):255-265

Two meteor events which were sighted in the Gujarat skies of India, were accompained by the visibility of sporadicE ionization on the ionograms recorded at Ahmedabad (Geog. Lat. 23·2°N, long. 72·30°E). The first event was the Dhajala fireball which flashed into the geoatmosphere along an E-N to W-S trail at about 20·40 h IST on 28 January 1976; the closest distance of the ground projection of meteor trail from Ahmedabad was 50km. The other event was a possible meteor group sighted over Ahmedabad on 28 May 1978, at about 21·10 h IST. This work describes the nature of the sporadicE ionization observed on Ahmedabad ionograms during the two events. Features of theEs echo during the Dhajala event which indicate that it could be of meteoric origin are discussed. Meteor theory is used to relate the observed ionization with the physical dimensions of the Dhajala meteorite as obtained by other workers.  相似文献   

Motion of charged particles in the magnetosphere     

G. K. Mukherjee  R. Rajaram 《Astrophysics and Space Science》1981,74(2):287-301

The adiabatic motion of charged particles in the magnetosphere has been investigated using Mead-Fairfield magnetospheric field model (Mead and Fairfield, 1975). Since the motion of charged particles in a dipolar field geometry is well understood, we bring out in this paper some important features in characteristic motion due to non-dipolar distortions in the field geometry. We look at the tilt averaged picture of the field configuration and estimate theoretically the parameters like bounce period, longitudinal invariant and the bounce averaged drift velocities of the charged particle in the Mead-Fairfield field geometry. These parameters are evaluated as a function of pitch angle and azimuthal position in the region of ring current (5 to 7 Earth radii from the centre of the Earth) for four ranges of magnetic activity. At different longitudes the non-dipolar contribution as a percentage of dipole value in bounce period and longitudinal invariant show maximum variation for particles close to 90° pitch angles. For any low pitch angle, these effects maximize at the midnight meridian. The radial component of the bounce averaged drift velocity is found to be greatest at the dawn-dusk meridians and the contribution vanishes at the day and midnight meridians for all pitch angles. In the absence of tilt-dependent terms in the model, the latitudinal component of the drift velocity vanishes. On the other hand, the relative non-dipolar contribution to bounce averaged azimuthal drift velocity is very high as compared to similar contribution in other characteristic parameters of particle motion. It is also shown that non-dipolar contribution in bounce period, longitudinal invariant and bounce averaged drift velocities increases in magnitude with increase in distance and magnetic activity.  相似文献   

Induced magnetic variations at Shillong in relation to regional geology     

Nandini Nityananda  D Jayakumar 《Journal of Earth System Science》1981,90(1):47-53

The Shillong plateau and Mikir Hills form a conspicuous feature in the geologically complex region of Northeastern India. From observations of geomagnetic variations at Shillong a consistent suppression of the vertical (Z) component of variation is noted. From previous analyses of a selected geomagnetic storm observed at Shillong, Ujjain and Jaipur, stations at nearly the same latitude, the complex demodulates ofZ variation at Shillong demonstrate this suppression. Results from a comparative study of bays and storm sudden commencements are also cited. An attempt to calculate induction vectors at Shillong was made but they were found to be indeterminate. However, a case for the presence of induced current concentrations near Shillong is strong, when these characteristics of geomagnetic variations are considered in the context of regional geology. Shillong and the Mikir Hills are the intruded northeastern remnants of the Indian Shield, that have been transported into the Eastern Himalayan syntaxis. But the present data are insufficient to delineate the path of induced currents in the Shillong region or to estimate their intensity.  相似文献   

Regional character of induced magnetic variations in India     

A.K. Agarwal  B.P. Singh  N. Nityananda 《Physics of the Earth and Planetary Interiors》1979,18(3):232-237

Variations recorded simultaneously at eight Indian stations during a magnetic storm are analysed to obtain the power spectra for each component using the fast Fourier transform. For two selected peaks, observed for H at all stations, at 49.5- and 70-min periods, a complex demodulation is performed for each component. From the variations thus obtained, horizontal polarization ellipses are drawn for four events of 49.5-min period. The variation of the demodulates and polarization ellipses at the stations shows a regional character which coincides with the physiographic grouping of the stations. Anomalously large Z variations are observed at the equatorial stations, which are near the sea. A distinct feature is the suppression of H at Trivandrum where the polarization ellipses confirm the E-W trend of the induced currents in this region. The overall similarity of the horizontal variations is demonstrated by these ellipses. Horizontal disturbance vectors at Annamalainagar, Trivandrum and Sabhawala confirm channelled currents located previously. At Shillong, the induced effects are evident and the currents are deduced to flow eastward, directly beneath the station.The overall regional similarities in variations are clearly manifested.  相似文献   

‘Sub-human’ beyond citizenship. A review of Nasir Uddin's The Rohingya.     

Prem Kumar Rajaram 《Singapore journal of tropical geography》2023,44(1):170-173

  相似文献   

Stability of a collisionless contact discontinuity     

R. Rajaram  G. L. Kalra  J. N. Tandon 《Astrophysics and Space Science》1980,67(1):137-145

The stability of a contact discontinuity in a collisionless plasma is examined. It is shown that the discontinuity can become unstable when the pressure component normal to the magnetic field is not continuous across the discontinuity. Even when the system is unstable, the growth rates are very small and unimportant in the context of wave propagation, except when the propagation is almost normal to the field. The instability could, however, lead to the slow dissipation of contact discontinuities in the solar wind and in the day side of the cusp region of the solar wind-magnetosphere boundary.  相似文献   

Undamped oscillations of collisionless stellar systems: Spheres,spheroids and discs     

S. Sridhar  R. Nityananda 《Journal of Astrophysics and Astronomy》1989,10(3):279-293

The collisionless Boltzmann equation governing self-gravitating systems such as galaxies has recently been shown to admit exact oscillating solutions with planar and spherical symmetry. The relation of the spherically symmetric solutions to the Virial theorem, as well as generalizations to non-uniform spheres, uniform spheroids and discs form the subject of this paper. These models generalize known families of static solutions. The case of the spheroid is worked out in some detail. Quasiperiodic as well as chaotic time variation of the two axes is demonstrated by studying the surface of section for the associated Hamiltonian system with two degrees of freedom. The relation to earlier work and possible implications for the general problem of collisionless relaxation in self gravitating systems are also discussed  相似文献