• Volume 98, Issue 3

      October 1989,   pages  223-308

    • Relationship between the southern oscillation/El Nino and rainfall in some tropical and midlatitude regions

      R P Kane

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      Association of ENSO (El Nino/southern oscillation) events with annual rainfalls in S. America, Africa, India, Australia and New Zealand was found to be poor except for India and Victoria. For these two regions the relationships were one-sided i.e. most of the ENSO were associated with droughts; but many droughts were not associated with ENSO. for some rainfall series, the relationships are significant and prominent periodicities existed in the long periodicity region.

    • Diffusion characteristics of the Kakinada Bay for effluent assessment

      A S Unnikrishnan V Asthana

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      The present study reports the determination of diffusion characteristics of the Kakinada Bay to choose a suitable marine outfall location for industrial discharge of effluents from a proposed fertilizer plant. The study consisted of dye diffusion experiments using Rhodamine-B, a fluorescent dye by the instantaneous release technique. Concentrations of samples collected at different time intervals were analysed using a fluorometer. Simultaneously, oceanographic data were also collected. The dye distributions were plotted based on the measured concentration values from the samples collected at various points in the patch. It was found that the movements of the patches depended on the tidal phase during the release. The computed values of diffusion coefficients were of the order of 0·2–2·9×103 cm2/s.

    • Observations of mid-troposhheric circulation from water vapour radiances of polar orbiting satellites

      M S Narayanan P K Pal P C Joshi M Mali Baby Simon

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      Water vapour tracers can provide useful information on winds at ≈ 500mb by observing the 6·7μ radiances. This fills the data gap in the cloud motion winds provided by conventional meteorological geostationary satellites. There is no geostationary satellite at present over the Indian Ocean with 6·7μ imaging capability to provide mid-tropospheric winds. The potentials of 6·7μ radiances, available from polar orbiting satellites, for mid-tropospheric circulation features have been examined in this study. Tiros-N satellite data of May 1979 and ECMWF level-IIIb wind data were analysed to relate the radiances with the streamlines. We find that the radiances of 6·7μ from orbiting satellites agree well with the wind field.

    • Canonical sound speed profile for the Central Bay of Bengal

      T V Ramana Murty S Prasanna Kumar Y K Somayajulu J S Sastry Rui J P De Figueiredo

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      Following Munk's canonical theory, an algorithm has been presented for computing sound channel parameters in the western and southern Bay of Bengal. The estimated canonical sound speed profile using these parameters has been compared with computed values for a set of CTD and hydrocast data. The analysis indicates appreciable variation in the perturbation coefficient ε even over short ranges, particularly in the eastern region. This has an important implication in ray tracing, where the range dependency of the acoustic field can be introduced with suitable modification. In the region where the channel axis is nearly symmetrical about the upper and lower bound, the canonical profile almost reproduces the computed one. The results of the exponential, stratified model lead to a reasonable/realistic fit with the ocean beneath the thermocline.

    • Wave-induced nearshore circulation along the Calangute-Candolim beach, Goa, west coast of India

      V Krishna Kumar C S Murty A K Heblekar

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      The wave-induced nearshore circulation model suggested by Noda has been modified and applied for three small segments along the coast of Goa. The present model incorporates the prevailing bottom topography and considers its variation along with the radiation stress as the driving force for the circulation. We find that the flow pattern is strongly dependent on bottom topography. While normal incidence of waves results in a cellular pattern of flow, meandering flows prevail for oblique incidence along the coast. The shoreward flows are always located over shoals while the rip currents prevail over channels. The onshore/offshore flows show magnitudes as high as 3·1 m/s, while those alongshore reach a maximum of 1·1 m/s. When compared with field observations these values are slightly higher.

    • Solar activity and radiative flux divergence in the tropical middle atmosphere

      K Mohanakumar

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      Results of a study on radiative net flux divergence at various heights of the middle atmosphere (15–80 km) over the tropical station, Thumba (8°N, 77°E), India, for a period of 12 years from 1971 to 1982 using M-100 rocket data are reported. Over Thumba mesospheric net flux divergence occurs during the descending phases and flux convergence takes place during the ascending phases of the solar cycle. The net flux divergence in middle stratosphere seems to have quasi-biennial variations. The total net flux divergence during a 11-year solar cycle is found to be highly negative in the mesosphere and strongly positive in the upper stratosphere, representing the heat source and sink regions in the middle atmosphere.

    • Anomalous SO4−Cl groundwater in the coastal aquifer, Kerala

      D Chandrasekharam

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      Groundwater in laterite along the northern part of the Kerala coast shows anomalous concentration of SO4 and Cl ions. Investigation based on the chemical characteristics of groundwater, rain and Arabian seawater together with results of the laterite-water interaction experiment and sea-aquifer water-chemical mixing models show that Tertiary sediments in this region are the main source contributing SO4 and Cl ions to the groundwater system.

    • Generation of low-frequency oscillations in the subsolar venus ionopause

      R N Singh Hari Om Upadhyay

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      The steep electron density gradient, the magnetic field curvature and the effect of gravity make the Venus ionopause region unstable. The onset of flute instability in the Venus ionopause plasma has been studied. The dispersion of waves and their growth have been studied using in situ measured data. The existence of low frequency waves in the subsolar magnetic field data ionopause region has been interpreted to arise as the result of flute instability.

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