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1.
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
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A portion of the aeromagnetic anomaly map of India, from 170 to 200 N and 78o to 84o 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
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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
5.
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
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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
8.
Considerable debate revolves around the relative importance of rock type, tectonics, and climate in creating the architecture of the critical zone. We demonstrate the importance of climate and in particular the rate of water recharge to the subsurface, using numerical models that incorporate hydrologic flowpaths, chemical weathering, and geomorphic rules for soil production and transport. We track alterations in both solid phase (plagioclase to clay) and water chemistry along hydrologic flowpaths that include lateral flow beneath the water table. To isolate the role of recharge, we simulate dry and wet cases and prescribe identical landscape evolution rules. The weathering patterns that develop differ dramatically beneath the resulting parabolic interfluves. In the dry case, incomplete weathering is shallow and surface parallel, whereas in the wet case, intense weathering occurs to depths approximating the base of the bounding channels, well below the water table. Exploration of intermediate cases reveals that the weathering state of the subsurface is strongly governed by the ratio of the rate of advance of the weathering front itself controlled by the water input rate, and the rate of erosion of the landscape. The system transitions between these end‐member behaviours rather abruptly at a weathering front speed ‐ erosion rate ratio of approximately 1. Although there are undoubtedly direct roles for tectonics and rock type in critical zone architecture, and yet more likely feedbacks between these and climate, we show here that differences in hillslope‐scale weathering patterns can be strongly controlled by climate. 相似文献
9.
The degree sheet Aeromagnetic maps up to 17‡N, acquired from the Geological Survey of India, have been manually redigitised
at 6 minute intervals to study the long wavelength anomalies over peninsular India. These data have been collected at different
survey altitude, epochs, flight line directions, etc. Great care has been taken to correct the total field map and remove
the contribution due to the core field and prepare an accurate crustal anomaly map. For the first time, a regional map, depicting
the NW-SE structural features north of the orthopyroxene isograd with the essentially E-W features to the south of it and
revealing several well known structures, is presented. The analytical signal is calculated to delineate the source fields
of these anomalies. It dramatically maps the charnockites and is able to delineate the orthopyroxene isograd. In the Dharwar
region the magnetic signatures are associated with the intrusives/ iron ore bodies. Thus, we find that the source rocks of
the aeromagnetic anomalies are the host province of charnockites in the SGT and the intrusives/iron ore bodies in the Dharwar
belt. Gravity residuals are calculated and a tectonic map of the region is presented from the combined geopotential data. 相似文献
10.
Data collected by Magsat have been extensively used by Indian scientists in studies of the crust beneath India. Results obtained
by various workers have been summarized and the reasons for differences in findings have been discussed. It is concluded that
methods that work well for higher latitudes do not give the best estimates of crustal field and magnetization in equatorial
regions. A better estimate of the crustal component is obtained when the external current contribution is estimated using
the symmetry properties of associatedX and Z-fields. Inversion technique that provides stable crustal magnetization in midlatitudes, becomes unstable near the equator.
Why such an instability arises and how it can be circumvented are discussed. That the Peninsular shield, the Ganga basin and
the Himalayas are three different geotectonic blocks is clearly reflected in the magnetization distribution. A thick magnetic
crust under Aravalli, Singhbum and Dharwar suggest these areas to be comparatively stable. In general, seismic, gravity and
heat flow data agree characteristically well with the magnetization estimates. 相似文献