Volume 92, Issue 1
March 1983, pages 1-97
pp 1-4 March 1983
Cosmogenic beryllium-10 activities have been measured in marine accumulations of up to ∼6 m.y age by conventional beta counting technique and by accelerator mass spectrometry. The two sets of data at10Be levels of 109–1010 atoms/g agree within the absolute errors of the two methods. The detection limit for10Be by the accelerator mass spectrometry is about five orders of magnitude lower than that with the beta counting method.
pp 5-13 March 1983
Variation of the strength of recurrent geomagnetic activity, which occurs just before a sunspot minimum, with local time is studied for a network of observatories covering different latitude and longitude zones. For this purpose, hourly averages of horizontal intensity(H) for each UT hour for 173 days, which are totally free of disturbances due to solar transients, have been subjected to spectral analysis. Well-defined spectral peaks associated with periodicities of 28, 14 and 9 days were present in almost all the spectra. The pattern of daily variation of the strength of the 27-day signal changes from a diurnal one at low latitudes to a semi-diurnal one near the Sq focus and in this region, the 14-day signal appears to have an independent origin irrespective of the longitude zone. A study of 27-day oscillation in mean dailyH field also indicates that apart from ring current modulation, both Sq and electrojet fields also undergo 27-day oscillations during the declining phase of a solar cycle possibly through the ionospheric wind system.
pp 15-30 March 1983
The magnetic measurements of declination (D), horizontal (H) and vertical (Z) components of earth’s magnetic field, collected from ground surveys between 1962 and 1966, are used to develop an analytical model of geomagnetic field variations over Indian region for the epoch 1965. In order to reflect spatial features with wavelengths of approximately 1000 km, sixth degree polynomial as a function of differential latitude and longitude is calculated by the method of least squares. The root mean square fit of the model to the input data is better than that accounted by the International Geomagnetic Reference Field for 1965.0. Isomagnetic charts drawn forD, H, Z and total force (F) reflect more details than that shown on world magnetic charts. Further, the values of the field at common repeat stations recorded between 1962 and 1974, after eliminating the field values for the epoch 1965.0, are used to get the secular variation as well as its spatial dependence again by means of polynomial which now includes coefficients which are functions of time and of geographical locations. The accuracy of coefficients is tested against the behaviour of secular variation at permanent magnetic observatories. The merits and limitations of the model are discussed.
pp 31-36 March 1983
Variations in a solar activity and their effect if any on the temperature of the stratopause are studied. Monthly mean stratopause temperatures during 1969–1976 and departures from the monthly mean value of eight-year period, determined for four equatorial rocket launching stations,viz. Ascension Island, Kwajalem, Fort Sherman and Thumba, are statistically compared with sunspot number departures. To study the effects of seasonal variation on stratopause temperature, the data have been divided into winter, summer and equinoctial periods. Seasonwise study indicates that the correlation between the stratopause temperature and sunspot number is positive and just below the significant level for Thumba and positive and highly significant over all the other stations with a better relationship in equinoctial periods than in both winter and summer. The estimated regression coefficients are positive and significant.
pp 37-43 March 1983
Almost saturated scintillations of radio beacons from geostationary satellites received at an equatorial station during night-time have been shown to occur even during complete absence of spreadF on the vertical incidence ionograms at the same location. These scintillation events were observed when the ionograms showed blanketing type of sporadicE layers simultaneously at different heights. It is suggested that strong equatorial radio wave scintillations during night-time are caused by multiple scattering between different levels of large plasma density gradients in theF or sometimes in theE regions of the ionosphere.
pp 45-55 March 1983
Indices of the equatorial electrojet and counter-electrojet in the Indian region have been evolved based on certain reasonable assumptions, by a criterion depending on the difference in the horizontal field strength between a station under the electrojet axis (Trivandrum) and a station outside the jet influence (Alibag). The indices enable one to characterize each day of the year by an appropriate index. Distribution, in the months, seasons and over the years, of the electrojet and counter-electrojet frequencies at Trivandrum during a 20-year period, 1959–78, is examined. The salient features of the distributions are: (i) Strong electrojets (range 50 nT) and the afternoon counter-electrojets occur, on an average, on about 50% of the days in the year; (ii) For the counter-electrojet, the monthly frequencies show an annual variation with a summer maximum, and for the strong electrojet, a semi-annual variation with maxima in the equinoxes; (iii) A secondary maximum is noted in January in the occurrence frequency of both counter-electrojet and strong electrojet events; (iv) Intense electrojets occur with greater frequency in September.
pp 57-61 March 1983
In this paper we report on the MEM power spectrum analysis of brightness temperature fluctuations observed at 2.8 GHz during the total solar eclipse of 16 February 1980. The observed periodicities range from 3.5 min to 64 min. These periodicities may arise due to spatial and/or temporal variations in the solar radio emission. The observed periodicities imply presence of scale sizes ranging from 70,000 to 600,000 km assuming that the brightness fluctuations arise because of spatial variation only. On the other hand, if these fluctuations are due to temporal variation, the observed periodicities correspond well to predicted modes of solar global oscillations.
pp 63-71 March 1983
A sophisticated method of measuring water levels is adopted to determine the groundwater potentialities in a typical weathered and fractured environment by storage method. The frequency of the rainfall has shown a direct bearing on recharging the groundwater system compared to the intensity of the rainfall. The Thiessen polygon method is used to determine the weighted average of the rainfall over the basin area to estimate the ground water infiltration rates. The long term average infiltration to the medium is established as 15% of the total rainfall.
pp 73-80 March 1983
The igneous alkaline rocks at Elchuru start from a parent ijolite-melteigite association to basic malignite, melalusitanite and shonkinite followed by nepheline syenites and then biotite lamprophyres (as dykes) at the waning phase of the evolutionary course of the complex. The distinct alkalinity of the rocks is manifested by the development of modal nepheline and calcic amphibole (kaersutite). For both the basic rocks,i.e. alkali gabbro and biotite lamprophyre, the percentages of normative nepheline are always higher than modal nepheline, indicating silica deficiency and alkali enrichment of the mafics. It is evident from detailed petrological and geochemical studies that the two basic members are very much akin to each other and there is no major deviation in their bulk chemistry.
pp 81-97 March 1983
Distribution of a number of trace elements in the Hinota kimberlite pipe, its overlying soil and selected vegetation is discussed in relation to the distribution of the same elements in the soils and vegetation overlying the quartzite country rock through which it is emplaced. The values of most elements in Hinota are similar to those of kimberlites from some other parts of the world, but Ni and Cu are higher. These elements in a “floating reef” of the Dhandraul Quartzite in the pipe closely follow the averages for other sandstones. It is observed that most elements in the soil over the kimberlite are significantly higher than in the soil over the surrounding country rock, particularly Ni, V, Cu and Cr. These could serve as reasonable guides to prospecting for kimberlites. Trace elements in the ash of selected trees growing over the diatreme and the country rock do not show any significant differences.