• Volume 89, Issue 2

      July 1980,   pages  121-276

    • Cosmic ray effects in the solar system objects

      N Bhandari M N Rao

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      Long term characteristics of solar and galactic cosmic rays, as revealed by the study of their nuclear effects in lunar, meteoritic and terrestrial samples are summarised. The data so far available on radioisotopes, noble gases and tracks, though limited, are consistent with nearly constant fluxes and composition during different epochs over billions of years; one exception is14C activity in the earths atmosphere over the past few hundred years, suggesting a variation in the solar activity. Other small or brief variations, which cannot be ruled out as yet, require better estimation of depth and size dependence of nuclear effects in rocks before they can be attributed to cosmic rays.

    • Cosmogenic and bomb-produced7Be in stratospheric air

      Prem Sagar P S Goel

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      Concentration of7Be has been measured in 15 air filters flown at 18·3 km in the latitudes 10 to 25°N and longitudes 80 to 96°W. Testing of nuclear weapons in atmosphere increased7Be considerably, on two occasions, above the expected cosmic-ray production level in the stratosphere. This provides evidence for the existence of interhemispheric mixing,via stratosphere.

    • On the growth and decay of irregularities in the ionosphere

      Hari om Vats M R Deshpande

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      It has been demonstrated that VHF/UHF scintillation data can be used to evaluate important physical parameters such as scale sizes, strength, growth and decay of irregularities in the equatorial ionosphere. These parameters are important in constructing electroject models. It is shown that large scale irregularities are generated first which later break into smaller scale sizes. During the decay phase, the small scale irregularities disappear first after followed by large scale irregularities. The generation and destruction time of these irregularities has been estimated to be around 20 min. In addition these irregularities affect propagation of radio waves from HF to UHF range which suggests the existence of a wide spectrum of irregularities in the ionosphere. It has been found that the scale sizes of daytimeE-region irregularities are smaller than those in theF-region during night-time. The growth rate of the irregularities seems to be larger in theE-region than in theF-region of the ionosphere.

    • Measurement of recharge rates in soils through detection of tritium produced in Chinese thermonuclear tests

      R N Athavale C S Murti

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      Variations in environmental tritium and moisture content with depth was measured at three sites in sandy-loam and sandy-clay-loam soils, sampled near Hyderabad in May 1974. The tritium input function for precipitation around Hyderabad for the years 1969 to 1973 was determined through measurements on available rain samples and through extrapolation of strontium-90 data for HASL network station at Rawalpindi.

      Three peaks noticed in the tritium input function and probably caused by Chinese thermonuclear tests in 1970, 1971 and 1972, could be matched with those sequentially identified in the soil profiles. This identification has helped in dating the soil moisture and in calculation of average annual recharge to groundwater. The recharge was found to be 15·4 cm and 14·6 cm for sandy-loam and 11·1 cm for sandy-clay-loam soils.

    • On the effect of the partial solar eclipse of 29 April 1976 on electron content

      G Sethia H Chandra M R Deshpande

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      Faraday rotation measurements made at a chain of stations and group delay measurements made at Ootacamund from ATS-6 are examined for the partial solar eclipse event of 29 April 1976. There is no evidence of eclipse-induced gravity waves in these measurements extending from Ootacamund near dip equator to Patiala (dip 45° N). Eclipse-induced fluctuations were however reported at Trivandrum, about 300 km south of Ootacamund.

    • Numerical simulation of the Indian monsoon

      P K Das

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      A review of current work in India on modelling experiments is presented. The experiments are designed to simulate different features of the Indian summer monsoon. The first part of the paper summarises the basic structure of a model, and the problems of computational design. Different grid structures and transformation of the vertical coordinate to include mountains are discussed. Experiments are suggested for minimising truncation errors by using different reference atmospheres, and by normal mode initialisation. A brief account is provided of the use of finite elements for numerical models.

      The latter half of the paper deals with different physical processes in the atmosphere. They are (i) the radiation balance of the atmosphere, (ii) clouds and precipitation, (iii) frictional effects, and (iv) sea surface temperature. The results of models developed in India are compared with those obtained by general circulation models. It is shown that present models succeed in simulating certain features of the monsoon fairly well, but further work is needed to simulate other aspects, such as, rainfall.

    • Some aspects of the large scale fluctuations of summer monsoon rainfall over India in relation to fluctuations in the planetary and regional scale circulation parameters

      D R Sikka

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      Year-to-year fluctuations of summer monsoon (June–September) rainfall of India are studied in relation to planetary and regional scale features. Anomalous epochs in the monsoon rainfall have been found to coincide with the epochs having anomalous patterns of temperature distribution in the northern hemispheric extratropics as well as with the spells of years having anomalous patterns of sea surface temperature distribution in the equatorial Pacific Ocean (EL-Nino phenomenon).

      Relationship between monsoonal rainfall and regional atmospheric circulation features is studied by compositing data of five good and five bad monsoon rainfall years over India. A comparison of the two data sets yields interesting relationships between the anomalous patterns of rainfall on the one hand and atmospheric parameters on the other. On the average parameters of monsoon depressions are more or less the same among the two types of composites. The most important distinguishing feature of good monsoon years is the greater frequency of cyclogenesis (monsoon lows included) on the regional scale which keeps the monsoon trough near its normal position and with concomitant higher cyclonic vorticity in the trough zone contributes to greater seasonal rainfall on the regional scale during good monsoon years.

    • Aircraft measurements of SST using IR-radiometer and temperature corrections due to atmospheric effects

      H S S Sinha S V Kasture V Satyan R M Pandya P A Solanki

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      Using an airborne scanning IR-radiometer, measurements of sea surface temperature (SST) were made from nine different levels in the Sandheads region of the Bay of Bengal on 5 October 1978. To retrieve SST from the observed radiances a temperature correction scheme, which uses the radiosonde data in the vicinity of flight area, has been generated. Atmospheric effects which have been considered include absorption due to water vapour and carbon dioxide, and the re-emission from different atmospheric layers. The radiances observed at different altitudes when corrected by our scheme yield a fairly consistent value of SST. The special ship measurements of SST, at the same location, are found to have very good agreement with the SST retrieved from the observed radiances using our scheme. The temperature corrections turn out to be 0·3 and 3·3°C at 600 and 3000 meters respectively for the type of atmosphere which has been used in our study.

    • Shift of quasi-stationary flow features during active and break monsoons

      R N Keshavamurty V Satyan S K Dash H S S Sinha

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      During our search for dynamical differences in monsoon flows between the active and break phases of the monsoon, we noticed some interesting differences which may have some dynamical significance and do not appear to have been highlighted so far. There appear to be shifts of quasi-stationary flow features both in the lower and upper tropospheres.

    • Some thermodynamical and microphysical aspects of monsoon clouds

      A Mary Selvam A S Ramachandra Murty R Vijayakumar S K Paul G K Manohar R S Reddy B K Mukherjee Bh V Ramana Murty

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      The thermodynamical and microphysical characteristics of monsoon clouds in the Poona, Bombay and Rihand regions were investigated using extensive aircraft in-cloud observations. The number of clouds sampled at Poona, Bombay and Rihand is 2199, 169 and 104 respectively.

      The temperatures inside the cloud are colder than its environment at Poona and Rihand. The maximum difference is about 3°C at the cloud base level and the difference decreased with height. At Bombay the difference is less than 1°C and at some levels the temperatures inside the cloud are warmer than its environment.

      The lapse rates of temperatures inside the cloud are slightly less than those in the immediate environment of the cloud. The environmental lapse rates are nearly equal to the saturated adiabatic value.

      The positive increments in liquid water content (LWC) are associated with the increments in temperature inside the cloud. Similarly positive increments in temperatures inside the cloud are associated with the increments in temperature of its immediate environment at the same level or the layer immediately above.

      The maximum cloud lengths observed at Poona and Bombay respectively are 14 and 3 km. The horizontal cross-section of LWC showed a maximum number of 13 peaks in clouds at Poona while only 7 peaks were observed at Bombay. The location of maximum LWC in the horizontal cross-section is more or less at the centre of the cloud. The LWC profile showed an increase with height from the base of the cloud at Poona and Bombay. There is no marked variation of LWC with height at Rihand.

      The total droplet concentration at different altitudes at Poona and Bombay is in the range 28–82 cm−3. The size distribution of cloud droplets experienced a broadening effect with increase in height from the cloud base at Poona. The broadening effect at Bombay is not as marked as that at Poona.

    • Capability ofBhaskara SAMIR to distinguish atmospheric water vapour and liquid water contents

      P C Pandey A K Sharma B S Gohil

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      An environmental model to compute microwave brightness temperatures for downward looking radiometers on board satellite is described. The effects of water vapour, oxygen and clouds on the brightness temperature have been studied for frequencies from 5 to 50 GHz for a standard tropical atmosphere. The effect of look angle on brightness temperture has also been investigated. Based on the model it has been shown that while the radiometers on boardBhaskara at 19·35 and 22·235 GHz are capable of giving the atmospheric water vapour and liquid water contents, the ability to distinguish these quantities is more for the combination of the frequencies 22·235 and 31 GHz.

    • Electrical resistivity anomalies over hydrocarbon bearing structures

      V K Gaur Sri Niwas N R Garg

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      The present study is aimed at working out the possible resistivity anomalies associated with hydrocarbon bearing structures. The anomaly due to a typical two-dimensional anticlinal structure filled with hydrocarbon, and overlying a basement of infinite resistivity was computed using the conformal mapping technique. A more realistic and elaborate model, which could not be simplified by conformal mapping, was studied using the finite element method. This model consisted of a two-dimensional anticlinal structure filled with oil or gas-embedded midway in a homogeneous layer which itself overlies a half-space of infinite resistivity, the electrical resistivity of the hydrocarbon bearing structure being simulated as infinite.

    • Study of microwave response of coal and sandstone samples

      R Singh Ramesh P Singh K P Singh

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      Detailed measurements of relative dielectric constant and loss tangent of coal and sandstone samples have been carried out in the X-band of microwave frequency range (8–10 GHz). The effect of moisture, saline and petrol content on the dielectric and loss tangent has been studied. The reflection and transmission coefficient of these samples have been computed. The application of such measurements to geophysical prospecting has been discussed.

    • Magnetic studies on charnockites of Palni Hills

      K Ramaswamy N Ramamurthy

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      The magnetic properties like coercive force, mean mass susceptibility and relative remanence of some charnockites of Palni Hills, South India collected at different altitudes were measured.

    • The possible influence of curvature and rotation on ocean currents

      R Narasimha

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      Recent laboratory investigations have shown that rotation and (streamwise) curvature can have spectacular effects on momentum transport in turbulent shear flows. A simple model that takes account of these effects (based on an analogy with buoyant flows) utilises counterparts of the Richardson number Rg and the Monin-Oboukhov length. Estimates of Rg for meanders in ocean currents like the Gulf Stream show it to be of order 1 or more, while laboratory investigations reveal strong effects even at |Rg|∼0·1. These considerations lead to the conclusion that at a cyclonic bend in the Gulf Stream, a highly unstable flow in the outer half of the jet rides over a highly stable flow in the inner half. It is conjectured that the discrepancies noticed between observation and the various theories of Gulf Stream meanders, and such phenomena as the observed detachment of eddies from the Gulf Stream, may be due to the effects of curvature and rotation on turbulent transport.

    • Age of Saurashtra miliolites by U-Th decay series methods: possible implications to their origin

      N Hussain N Bhandari K R Ramanathan B L K Somayajulu

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