• Volume 98, Issue 2

      July 1989,   pages  133-222

    • Upland erosion in a mixed pine forest ecosystem

      K D Sharma J F Correia

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      Starting from basic erosion principles an upland soil erosion model to predict soil loss in humid subtropical monsoon climate by saturation overland flow from individual storms on forested hillslopes can be derived in the formQs=nx2kfSQ, where Qs, is the total soil loss for a storm event,n the roughness coefficient,x the downslope distance,kf the soil erodability factor, S the slope, α the slope exponent andQ the runoff. An mixed pine forest ecosystem hasn = 0.58 and α = 21.

    • Magnetotelluric survey across Singhbhum granite batholith

      K K Roy C K Rao A Chattopadhyay

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      Magnetotelluric soundings have been carried out across the archaean terrain of Singhbhum granite batholith from Bangriposhi to Keonjhar for a distance of about 100 km. One-dimensional inversion models reveal that the depth of the moho varied between 23 and 40 km. The depth of the lithosphere asthenosphere boundary varied from 58 to 76 km. A zone of higher electrical conductivity detected at the base of the lower crust just above the moho is present along the entire profile. Signals within the range of 0.25 to 600 seconds, which crossed the coherency threshold of 0.8 to 0.9, could be stacked. Resistivity ranges of the crust mantle silicates below Singhbhum granite batholith vary over a wide range. Resistivity ranges are (i) 30,000–80,000 ohm for Singhbhum granite phase II, (ii) 2,000 to 9,000 ohm-m for Singhbhum granite phase III, (iii) 250 to 2,200 ohm-m for lower crust (iv) 3,000 to 47,000 ohm for the upper mantle and (v) 200 to 2300 ohm-m for the asthenosphere. Sharp break in electrical resistivity at the (i) upper crust-lower crust (ii) lower crust upper mantle and (iii) lithosphere-asthenosphere boundary is obtained along the entire profile. Signals could see up to 100 km below the granite batholith. Singhbhum granite phase II and III could be demarcated on the basis of resistivity. Low resistive zones in the lower crust and upper mantle might have formed due to (i) water (ii) combined effect of water and carbon and (iii) high temperature and partial melt.

    • Mineralogy and chemistry of banded iron formations (BIF) of Tiruvannamalai area, Tamil Nadu

      N Subba Reddy A N Sashidhar

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      The mineralogy and chemistry of banded iron formations (BIF) of Archaean high grade granulite gneiss belt of Tiruvannamalai area are presented here. The BIF of this area is chemically different from those around the world. The iron formations and associated granulites are of different origin namely metasedimentary and metavolcanic respectively.

    • Holocene marine transgression as interpreted from bathymetry and sand grain size parameters off Gopalpur

      K Mohana Rao G V Rajamanickam T C S Rao

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      Grain size statistical parameters of the surface sediment samples collected from the innershelf off Gopalpur were calculated using graphic and moment methods. Fine-grained sand present up to 15m water depth shows symmetrical skewness and good sorting. These are leptokurtic. The coarse-grained sand beyond 15 m water depth has positive or negative skewness and moderate sorting. These are platy kurtic. Bivariate plot of mean vs skewness indicates two types of sample spread, keeping approximately 2.3ϕ mean as the demarcating boundary suggesting the presence of dune and beach types of sands. The study of log-probability sub-populations further supports these two types of sand as dune with single dominant saltation and beach with two distinct saltation populations. CM patterns suggest the role of rolling and graded suspension. The irregularity observed in bathymetry coincides with difference in the nature of sands within and beyond 15 m water depth. The behaviour of the grain size parameters and the associated bathymetrie features suggest the presence of relict environments of dune and beach.

    • Occurrence of thorite and radioactive zircon in syenite pegmatite, North of Ashwaraopet, Khammam district, Andhra Pradesh, India

      K Surya Prakash Rao R S N Sastry Gautam Roy

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      This paper reports the occurrence of thorite and confirms the earlier find of radioactive zircon by Subbarao, Murali and others from syenite pegmatite in the Vinayakapuram-Kunavaram alkaline belt in the Khammam district of Andhra Pradesh, India. Thorite has also been found as residual concentrations in soil overlying the pegmatite.

    • Simulation of a winter circulation over India using a global spectral model

      S K Dash B Chakrapani

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      A primitive equation spectral model has been successfully integrated for five days starting with the initial data of 26 February 1982. The geopotential heights and wind strengths are well predicted up to day 3. The 24-hour accumulated precipitation of the model reasonably agrees only up to two days, with the observed rainfall under the influence of western disturbance that prevailed over Afghanistan, Pakistan and north India till 3 March 1982. For one day global integration of the model, the CPU time requirement in Cyber 170/730 is about one hour.

    • Phase space analysis of Indian summer monsoon rainfall over subdivisions

      V Satyan

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      Indian summer monsoon seasonal rainfall for the period 1871–1986 over the meteorological subdivisions has been analysed using the method of deterministic chaos. It is shown that a strange attractor underlies the monsoon evolution in each subdivision. The dimensionality of the attractor and the number of key variables necessary to model the subdivisional dynamics have been determined.

    • Latent and sensible heat fluxes under active and weak phases of the summer monsoon of 1986

      P N Vinayachandran Y Sadhuram V Ramesh Babu

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      An analysis of the meteorological data collected by the research vessel ORV Sagarkanya for the mean latent and sensible heat fluxes over the Arabian Sea has indicated appreciable changes between active and weak phases of the southwest monsoon of 1986. We suggest that: (a) the presence of a core of low level winds associated with the Somali jet and its southward shift during the season, along with (b) a ridge in surface pressure over the central Arabian Sea could be responsible for the deficit in monsoon rainfall along the west coast of India in 1986.

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