• Volume 94, Issue 2

      July 1985,   pages  77-186

    • Detection of large scale electron density irregularities duringips observations at 103 MHz

      S K Alurkar H O Vats R V Bhonsle A K Sharma

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      Angular displacements in the positions of the quasar 3C 298 were observed during its interplanetary scintillation (ips) observations made using a correlation interferometer at 103 MHz at Thaltej near Ahmedabad. These changes in the apparent positions of the source could be seen as variations in the declination of 3C 298. Two possibilities which might cause such effects are considered; refraction of the radio waves either in the earth’s ionosphere or in the interplanetary medium (ipm) by large scale plasma density inhomogeneities. Order of magnitude calculations for both are presented. Further studies using two-site observations are suggested to decide between the two mechanisms.

    • Basal flow rate of Changme-Khangpu glacier, Sikkim Himalaya based on32Si and210Pb chronology

      V N Nijampurkar

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      Using environmental radioisotopes silicon-32 and lead-210, the radiometric ages of ice at the surface and at 5 m depth at the snout of the Changme-Khangpu (ck) glacier have been calculated to be 100 and >650 years respectively. Based on i) these age estimates, ii) a net uniform accumulation rate of 0·7 m/yr of ice in the accumulation zone; and iii) applying a simple ice flow model assuming melting of ice of 1 cm/yr at the base of the glacier, it is demonstrated that the average basal flow rate of theck glacier is much smaller (at least by a factor of three) than that of 40 m/yr estimated for the surface ice. This observation is in good agreement with the earlier work on basal flow rates and indicates that the deeper ice near the bed rock travels much slower than the surface ice.

    • An analytical technique for rapid determination of surface rock density

      G Ramadass S M Varaprasada Rao M S Vijaya Raghava

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      Computation of the coefficient of correlation between the Bouguer reduced gravity and the ground relief apparently helps minimize the subjectivity inherent in the Nettleton’s method of surface rock density determination. The ideal density is the one that results in zero correlation between them. The iterative procedure in sweeping the calculations through the range of densities chosen can be avoided by taking advantage of the linear relationship between this coefficient and the density. Linear interpolation is therefore suggested to arrive at the ideal density. The suggested procedure consequently consists of correlation coefficient computations for the two-density extremum values within which the density of the surface rock formations is expected to lie. The computer program for this method is also presented. The procedure involved and the efficacy of the method are illustrated with some practical analyses.

    • Preliminary studies on the geochemistry of the Cauvery river basin

      V Subramanian L van t’ Dack R van Grieken

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      Samples of water and sediments were collected over a three year period from the entire region of Cauvery river basin excluding the estuary. On the basis of our observations, we have calculated the average composition of the Cauvery river at several locations from the catchment to the river mouth, the downstream profile of sediment load, annual erosion rates, solute and sediment fluxes and have predicted on long term changes. The sediment chemistry was determined by x-ray fluorescence (xrf) technique, and calculated mean compositions of the Cauvery and its tributary bed and the suspended sediment were compared to those of world average river sediments. Downstream profiles of some of the elements appear to be controlled by size and mineralogical characteristics besides local factors specific to the location of the samples. Interelemental relationships indicated good correlation among the transition elements indicating their co-genetic behaviour within the drainage basin.

    • Anomaly map ofZ component of the Indian sub-continent from magnetic satellite data

      M G Arur P S Bains Jeevan Lal

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      An anomaly map of the Z component has been produced for the region of the Indian sub-continent for the first time by the Survey of India usingmagsat data. Data of thousands of kilometres of satellite tracks of varying altitude have been reduced to a common elevation of 400 km by removing the external field and linear trend. The entire data was plotted on a map of 1:6 M and mean values of 2°×2° blocks then accepted for contouring. A prominent magnetic low is reflected over the Himalayas and a prominent high over the Indian peninsula. The dividing line of positive and negative anomalies between the Himalayas and Deccan Traps falls along the Narmada lineament.

    • Summer cooling of the Arabian Sea—a review

      J S Sastry V Ramesh Babu

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      The summer cooling of the Arabian Sea has been reviewed in relation to the dynamic and thermodynamic processes. The differences in the quantum of cooling in the coastal regions have been attributed to the variations in the strength of coastal upwelling along the respective coasts. In the central portions of the Arabian Sea, the thickness of the surface layer and the thermal structure appear to be predominantly governed by the turbulent mixing of cold waters entrained into the surface layer in association with the deepening of current shear zone. The surface heat losses during the passage of a cyclone over the east central Arabian Sea account for only 40% of the total heat change in the surface layer while the rest is lost into the interior. Also presented are climatological mean patterns of the forcing parameters and their variations during certain years.

    • Monthly-mean wind stress along the coast of the north Indian Ocean

      Satish R Shetye S Satheesh Chandra Shenoi M K Antony V Krishna Kumar

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      Monthly-mean wind stress and its longshore and offshore components have been computed using the bulk aerodynamic method for each of a string of 36 two-degree-latitude by two-degree-longitude squares along the coast of the north Indian Ocean. The data source for the computation is the sixty-year mean resultant winds of Hastenrath and Lamb. The main features exhibited by the components, taking the longshore components as positive (negative) when the Ekman transport is away from (towards) the coast, are: (1) Along the coasts of Somalia and Arabia, the magnitude of the wind stress is among the highest in the north Indian Ocean, and its direction is generally parallel to the coastline. This results in a longshore component which is large (as high as 2·5 dyne/cm2) and positive during the southwest monsoon, and weaker (less than 0·6 dyne/cm2) and negative during the northeast monsoon. (2) Though weak (less than 0·2 dyne/cm2) during the northeast monsoon, the monthly-mean longshore component along the west coast of India remains positive throughout the year. The magnitude of the offshore component during the southwest monsoon is much larger than that of the longshore component. (3) The behaviour of the wind stress components along the east coast of India is similar to that along the Somalia-Arabia coast, but the magnitudes are much smaller.

    • Global temperature changes: relative importance of greenhouse constituents of the atmosphere as calculated with a 1-d radiative-convective model

      M Lal K C S Rao

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      Most modelling endeavours concerning the CO2-climate problem address only the question of the climatic response to increasing atmospheric carbon dioxide, while the amounts of other atmospheric gases remain fixed. But associated changes, either climatologically or anthropogenically induced, of minor atmospheric constituents can also be of significance in producing a substantial global warming. We have analysed the climatic response to changes in a number of atmospheric trace gases as they may enhance or counteract CO2-induced warming if their abundance should change. A comparison of the increase in equilibrium global-mean surface temperature due to plausible changes in the concentration of several trace gases in the atmosphere based on our calculations with a one-dimensional radiative-convective model is presented in this paper. Our results indicate that roughly 35% of global surface warming could be due to changes in trace gases other than CO2 and water vapour. The possible climatic consequences of the ongoing anthropogenic changes in the minor constituents of the atmosphere are also discussed.

    • Interaction of monsoon with northern hemisphere mid-latitude circulation

      S T Awade M Y Totagi S M Bawiskar

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      Fourier analysis has been used for the monthly mean northern hemispheric geopotential height for the levels 700 mb and 300 mb for the months April through August in bad monsoon years (1972, 74 and 79) and in years of good monsoon rainfall over India (1967, 73, 77). From the Fourier coefficients the transport of momentum and of sensible heat have been computed in wave number domain.

      Waves 1 to 3 show contrasting features during years of good monsoon and bad monsoon. Northward transport of momentum across subtropical latitudes is larger in good monsoon years, while northward transport of sensible heat is larger in bad monsoon years. In good monsoon years there is a large divergence of momentum in the subtropics while there is a large convergence of momentum in the mid-latitudes. In bad monsoon years there is a large divergence of sensible heat in the sub-tropics, but a large convergence in the mid-latitudes.

      These quantities show similar features in pre-monsoon (April to May) during good and bad monsoon years.

    • Short range prediction with a multi-level primitive equation model

      S S Singh

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      A five-level primitive equation model in a (x, y, p, t) coordinate system has been developed. A fairly sophisticated scheme of physical processes has been incorporated in the model. The model physics include air-sea interaction, cumulus parametrization, large scale condensation, dry convective adjustment, horizontal and vertical diffusion and simulated radiation. The initial balance between mass and motion fields has been obtained through a dynamic initialization scheme. The model has been integrated upto 48 hr using input data of a case of monsoon depression. The results of initialization and forecast have been presented and discussed. Wind, temperature and vertical velocity fields have been found to retain the observed map features; after the initialization, however, the surface pressure has been considerably modified. The model produced a reasonably good forecast up to 24 hr as far as the flow fields, rainfall region, structure of the depression and the movement of cyclonic circulation were concerned and beyond that damped rapidly. The rainfall rates were underestimated. Some of the shortcomings of the model are also discussed.

    • Correction of the paper “A study of meteorite falls”

      Frans E Wickman Carl D Palmer

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