• Volume 97, Issue 2

      December 1988,   pages  117-192

    • Cosmic-ray production rates of neon isotopes in meteorite minerals

      N Bhandari

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      The rates of production of21Ne and22Ne in spallation reactions, both due to solar as well as galactic cosmic rays, in some major meteoritic minerals, e.g. olivines, feldspars and pyroxenes, are calculated using their energy spectra and excitation functions. The production profiles of21Ne and22Ne due to galactic cosmic rays, and the22Ne/21Ne ratio depend upon the size of the meteoroid. The22Ne/21Ne ratio is very sensitive to the abundance of sodium and consequently its depth profile is distinctly different in feldspars, the ratio increasing with depth rather than decreasing as in pyroxenes and olivines. In the near-surface regions, up to a depth of 2cm, production due to solar flare protons dominates, giving rise to a steep gradient in isotopic production as well as in the22Ne/21Ne ratio. Composite production profiles are given and compared with measurements in some meteorites.

    • Northward propagation of the 30–50 day mode in the Indian monsoon region

      R N Keshavamurty V Krishnakumar V Kasture

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      A highly simplified zonally symmetric system of equations is used to understand the basic mechanism of the northward movement of the 30–50 day oscillation in the Indian monsoon region. Zonally symmetric perturbations are used on the July mean basic flow in the Indian region. A two-level model is employed. A simple parametrization of cumulus heating is included. An expression is derived for the northward phase speed. A right order of magnitude for the phase speed is obtained. The northward movement appears to be controlled by the basic zonal wind profile and cumulus heating.

    • Spectra of different fluxes over the arid and semiarid zones of northwest India during MONEX 1979

      U S Singh Daya Shanker R K Singh

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      Fluxes of heat, momentum and the kinetic energy over the arid and semiarid regions of Indian Peninsula have been computed. Spectral analysis of these fluxes at 50 mb interval were performed at each level in the vertical up to 300 mb surface. The eddy latent heat transport is governed essentially by short- and long-range periodicities. A 5-day periodicity is generally present in the vertical mean eddy fluxes. Long-range periodic oscillations are more pronounced in the extreme north of the Indian subcontinent. Dominance of medium-range periodicity is observed in all the fluxes except latent heat.

    • Satellite-tracked drifting buoy observations in the south equatorial current in the Indian Ocean

      S R Shetye G S Michael

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      Three satellite-tracked drifting buoys released in the south equatorial current in the Indian Ocean followed the path of the current moving westward approximately zonally in the vicinity of 10 S latitude. On nearing the east coast of Africa two buoys moved north and the third moved south. Over the open sea regime the buoys moved with a speed of approximately 30 cm/s at an angle of about 35° to the left of the wind. The overall tendencies seen in the buoy drift are similar to those observed elsewhere in the world oceans.

    • Retrieval of cloud classification parameters using two-dimensional fast Fourier transform

      M Mohan Lakshmi Bhaduri Vijay K Agarwal

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      A method is presented for the retrieval of classification parameters of clouds observed by satellite-borne imaging systems. It is based on a two-dimensional fast Fourier transform of cloud images and an analysis of their power spectra. The parameters retrieved provide quantitative information on mean brightness, size, shape and directional properties of clouds. The efficacy of the subdivision of the original cloud image into smaller regions and the determination of individual parameters is demonstrated by applying this procedure to some NOAA and INSAT cloud images.

    • Spectral width parameter for wind-generated ocean waves

      C xxxV K Prasada Rao

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      An evaluation of the spectral width parameter for wind-generated ocean waves is presented based on the analysis of wave data obtained through the ship-borne wave recorder fitted to RVGaveshani. The coverage of wave data includes deep as well as shallow waters on the east and west coasts of India. Considering that the spectral width parameter ɛ0 derived from Tucker's wave analysis provides a reasonably accurate estimate, a comparative study has been made for the other band-width definitions available in the literature. The results indicate some bias in the estimation of spectral width information using higher-order moments, e.g. ɛS andv, and with the alteration of spectral forms that are usually associated with multiple- or single-peaked wave spectra. Such a bias is not seen in the case of Goda's peakedness parameterQp with variation of spectral form. The effect of the ratio of the high-frequency cut-off to the spectral peak period on ɛS,v andQp is also investigated.

    • Water characteristics and transport of the Antarctic circumpolar current in the Indian Ocean

      P M Muraleedharan Basil Mathew

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      Geostrophic velocities are computed across meridians 37 °E and 105 °E using hydrographic data. The estimated mass transport is represented on a temperature-salinity diagram. The characteristics of the water within the Antarctic circumpolar current at 37 °E and 105 °E are discussed. The computed transport agrees with the previous estimates. Transports due to the current between 45 °S and the Antarctic continent at these two meridians are comparable. The westerly flow south of 42 °S at 105 °E is associated with a cyclonic eddy which appears to be a permanent feature, whereas the one at 50 °S is related to the topography of the region.

    • Selection of optimum frequency of a wind scatterometer

      Abhijit Sarkar Raj Kumar Mannil Mohan

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