The dip equator over Peninsular India and its secular movement

A ground geomagnetic survey conducted in peninsular India has demarkated the dip equator for the epoch 1991.0. A well-defined southward migration in the last two decades is evident. The secular trend in the vertical component and the direction of the migration in the India zone are shown to be consistent. The migratory movement of the dip equator in different longitude sectors is compared to highlight the complex nature of the secular trends.     

Results of the studies of monsoon circulation with radon as a tracer

Radon-222 activity levels have been measured at deck level in regions of the Arabian Sea, Indian Ocean, and Bay of Bengal during the summer monsoon periods of 1973, 1977, and 1979, as part of the Monex programme. The aim of the measurements was to find the source regions of the monsoon air and the variations in its composition under different synoptic conditions. The radon data confirm that the monsoon air is predominantly of southern-hemisphere origin, with a small continental component. The continental component, as indicated by radon values, increases at higher latitudes and seems to vary with different circulation patterns in the synoptic scale. The use of radon as a tracer in monsoon studies is thus demonstrated.     

Total precipitable water in the atmosphere over India

Electromagnetic radiation, in its passage through the atmosphere, is attenuated by absorption and scattering by atmospheric gases, dust and aerosols. The most important absorber is water vapour and the most significant parameter in atmospheric absorption studies is the total precipitable water in the atmosphere. The present paper summarises the results of a study made to compute the total precipitable water in the atmosphere over India using radiosonde and other data, as part of a programme for the computation of direct, global and diffuse solar radiation at the ground from the solar constant. Using values of air temperature and dew point from the ground up to 250 mb at 19 radiosonde stations and surface water vapour mixing ratio values at 105 surface observatories in India, precipitable water amounts have been computed for 124 stations, for each month and for the whole year. The paper describes the techniques used to extend the total precipitable water amounts derived from radiosonde data at 19 stations to 124 stations covering the major climatic zones in the country and presents the results in the form of 12 maps showing the spatial and temporal distribution of total precipitable water over India     

Application of the Linear Prediction filters in equatorial electrojet studies

Wiener filters are derived from the horizontal field data of two adjacent equatorial electrojet stations, Adis Ababa and Trivandrum from several sequences of quiet days. The time invariant property of the filter is established and the filter is applied to conditions marked by afternoon counter electrojet events. The prediction efficiency is shown to be consistently high. Possible uses of this technique in studies related to generating mechanisms of counter electrojet events and the day-to-day variability in electrojet currents are indicated. Inter-relationships and day-to-day variability of different components of the fields at the two stations are highlighted.     

Daily variation of geomagnetic field at low latitudes associated with stable solar wind flow

Mean diurnal variation ofH at low and equatorial latitudes is computed for days in the vicinity of passage of ‘quiet’ solar wind. It is shown that the prepassage magnitude of the diurnal variation is appreciably larger when compared to post-passage intervals at low latitudes but the difference vanishes in the electrojet region. It is suggested that the Sq current system moves towards dip equator immediately following quiet wind conditions relative to earlier periods. It is also shown that during conditions of stable solar wind, the solar wind proton density is inversely related to the electrojet strength, while at low latitudes outside the jet influence, there is no clear association.     

Geophysical and tracer studies to detect subsurface chromium contamination and suitable site for waste disposal in Ranipet,Vellore district,Tamil Nadu,India

A chemical factory near Ranipet town in Vellore district, in the state of Tamil Nadu, India produced chromium-based inorganic chemicals. The factory area in granite gnessic terrain receives an average annual rainfall of 1,000 mm. About 1.5 lakh tons of solid wastes rich in hexavalent chromium (Cr⁶⁺), spreading over an area of 14,000 m² (about 3.5 acres), having about 4 m thickness, is accumulated in an open yard within the factory premises. The soil and groundwater in and around the factory area are contaminated with Cr⁶⁺ leached from dump site. Cr⁶⁺ is carcinogenic in nature and when leached in water can lead to respiratory disorders. Resistivity surveys comprising vertical electrical sounding, multielectrode resistivity imaging, drilling of bore wells, chemical analysis of soil, formation and groundwater samples and bore hole tracer studies were carried out within the factory and adjoining areas to decipher subsurface geology, hydraulic behavior of dyke as natural barrier and lateral and vertical extent of pollution zone in and around the chromium dump site. The data obtained were integrated and interpreted for understanding the pollution migration and its impact on environment. Remedial measures are suggested for containing the contamination.     

Daily variation of the geomagnetic field in equatorial region and sector boundary passage

The mean daily range in horizontal intensity at low latitudes shows a significant departure on the day of a sector boundary passage in relation to its magnitude on adjacent days with a measure of dependence on phase of the solar activity. It is shown that this arises because of a substantial difference, in the nature of the response to sector boundary passage, between the instantaneous maximum field and minimum field. From the fact that the responses at three stations spanning the latitudes near dip equator to that near the focus of Sq currents are almost identical, it is suggested that the cause of the observed feature is primarily disturbance and is essentially non-ionospheric. Differences in the nature of responses between pre-1957 and post-1957 periods reported earlier in the planetary indices or low latitude disturbance indices are shown to be true for the daily range, maximum and minimum fields at low latitudes.     

The effect of angle-dependent non-coherent electron scattering and partial redistribution on the polarization of resonance lines

The polarized radiative transfer equation is solved when angle-dependent partial redistribution and non-coherent electron scattering are included as line-scattering mechanisms. A static atmosphere with plane parallel symmetry is assumed. Test calculations are used to illustrate the effects of the electron-scattering coefficient, the thermalization parameter and the continuous absorption coefficient on the line polarization. Results of angle-averaged and angle-dependent redistribution functions are compared and it is shown that angle-dependent functions should be used to model the wing polarization of optically thin lines. The lower the continuous absorption compared with the electron scattering, the higher the wing polarization.     

High resolution facies record on late Holocene flood plain sediments from lower reaches of Narmada Valley,Western India

A high resolution quantitative granulometric record for site Uchediya [21°43′2.22″ N, 73° 6′26.22″ E; 10 m a. s. l.] gives understanding towards accretion history of the late Holocene flood plain in the lower reaches of Narmada River. Two sediment facies (sandy and muddy) and seven subfacies (sandy subfacies: St_MS+FS+CS, Sm_FS+MS, Sl_FS+VFS, and St_{MS + CS}; muddy subfacies: Fm_SILT+VFS+FS, Fm_SILT+VFS (O) and Fm_SILT+VFS (T)) are identified based on cluster analysis supplemented with sedimentary structures observed in field and other laboratory data. Changes in hydrodynamics are further deduced based on various sedimentological parameters and their ratios leading to arrive at a depositional model.