• Volume 93, Issue 4

      November 1984,   pages  343-464

    • Long and short term relationships between solar wind velocity and geomagnetic field at low latitudes

      G K Rangarajan

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      Solar wind velocity control of low latitude geomagnetic field both on long and short term basis is studied. It is shown that semiannual averages of the low latitude field is inversely related to solar wind velocity and that there is a dominant local time dependence of the relationship. Strongest correlation are confined to the local afternoon hours. It is also shown that for a duration when the solar wind velocity exhibits significant recurrent pattern the low latitude geomagnetic field also depicts strong solar synodic rotation periodicity of 27 days with significant coherence with velocity. The low latitude field on a short term basis is influenced by variable solar wind velocity with a delay of about 1–2 days. During the period of systematic recurrent pattern in solar wind velocity even the quiet-time night field at equatorial and low latitudes show a strong dependence on velocity indicative of the solar wind control of the quiet-time proton belt encompassing the earth.

    • Delineation of long-wavelength magnetic anomalies over central India by rectangular harmonic analysis

      B R Arora S Y Waghmare

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      The method of rectangular harmonic analysis is applied to the geomagnetic field data from central India to isolate long wavelength magnetic anomalies associated with largescale crustal structures. The long-wavelength anomalies have accounted for approximately 20 % of the spatial variability of the residual magnetic field over the International Geomagnetic Reference Field. On the magnetic anomaly map, reflecting the surface expression of longwavelength anomalies, the Tapi-Narmada-Son zone is characterized by a feeble positive anomaly bounded by a strong negative anomaly. The anomaly pattern is believed to be caused by the large-scale undulation in Moho and related variations in the thickness of the lower (basaltic) crust. The other two prominent anomalies, the magnetic low striking northwest and the magnetic high trending east-northeast, appear to be related to the deep structural feature of the Godavari graben and the eastern Rajasthan lineament respectively.

    • Effect of relative humidity on the angular distribution of scattered light intensity for rural and urban aerosols

      R K Goel N C Varshneya T S Verma

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      The change in atmospheric relative humidity affects the physical and optical properties of aerosol particles. It would be interesting to study the effect of an increase in relative humidity on the angular scattering of light by aerosols (by incorporating the changes due to it as the complex refractive index and the parameters of the size distribution function). In the present paper we have computed the angular scattering function for rural and urban aerosols, for light of wavelength 0.55 μn. The results obtained for these two models, representative of different environments, are interesting and show some discriminating features.

    • Interannual and long-term variability of Indian summer monsoon rainfall

      B Parthasarathy

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      Analysis of summer monsoon (June to September) rainfall series of 29 subdivisions based on a fixed number of raingauges (306 stations) has been made for the 108-year period 1871–1978 for interannual and long-term variability of the rainfall. Statistical tests show that the rainfall series of 29 sub-divisions are homogeneous, Gaussian-distributed and do not contain any persistence. The highest and the lowest normal rainfall of 284 and 26 cm are observed over coastal Karnataka and west Rajasthan sub-divisions respectively. The interannual variability (range) varies over different sub-divisions, the lowest being 55 and the highest 231% of the normal rainfall, for south Assam and Saurashtra and Kutch sub-divisions respectively. High spatial coherency is observed between neighbouring sub-divisions; northeast region and northern west and peninsular Indian sub-divisions show oppositic correlation tendency. Significant change in mean rainfall of six sub-divisions is noticed. Correlogram and spectrum analysis show the presence of 14-year and QBO cycles in a few sub-divisional rainfall series.

    • Ageostrophic instabilities in a two fluid system with rotation

      N Ramanathan D B Rao

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      The stability of synoptic scale waves formed on a frontal surface is studied including nongeostrophic effects with the basic flow subjected to both vertical and horizontal shear. Spectral method is used to obtain the desired solutions. The stability characteristics of the developed unstable modes are presented as a function of shears of the basic flow. With the inclusion of barotropic shear the spectrum of instabilities increase. The lower speeded member of the mixed mode (gravitational-rotational) pair is influenced by the barotropic shear in the basic current and it appears at lower vertical shears. The structure of the height perturbations are utilized to distinguish the various unstable modes developed in the system together with their stability characteristics. This investigation has shown that the ageostrophic effects can be a significant factor in the development of synoptic scale waves on a frontal surface.

    • Seasonal variability of the temperature field off the south-west coast of India

      Satish R Shetye

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      The temperature field in the coastal region off south-west India exhibits a wellmarked annual cycle. Around March the isotherms develop an upward tilt near the coast. The magnitude of the tilt increases continuously till August, then decreases and vanishes in November. To check the hypothesis that this feature is in response to the local wind, we have used the resultant wind data to determine the annual march of the wind stress. It is found that though weak during November–March, the monthly-mean longshore component of the wind stress is always conducive to coastal upwelling and follows a pattern similar to that of the isotherm tilt. We interpret this result to indicate that coastal processes in the area during April–October are controlled by the longshore component of the local wind stress in accordance with the classical model for a coastal upwelling system. During November–March, when the wind stress is weak, it appears that the influence of the longshore density gradient, which persists at the surface during this period, dominates over the effect of the wind.

    • A digital model to evaluate the water balance in a typical hardrock environment

      B H Briz-Kishore

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      A digital model was designed and developed to study the water balance situation in a typical hardrock environment near Hyderabad, Andhra Pradesh. The model was calibrated over a period of six years with observed field hydrographs. An optimum error factor of 0.001 m was chosen and the computer took 47 iterations for outputting the results with the desired accuracy. Prognostic studies were carried out with progressively increasing draft conditions and water levels were observed to be declining even when the draft was less than the recharge. The analysis of the experiments further amended the belief of the earlier workers.

    • Inter-element relations in some alkaline suites of the Eastern Ghats Precambrian belt

      Mihir K Bose Monoj Maitra Asish K Ghosh Roy

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      Element interrelations, with particular emphasis on alkaline earth metals, have been studied quantitatively for three alkaline suites of the Eastern Ghats Precambrian belt. Geochemical characterisation brings the Koraput and the Kunavaram suites closer, relative to the Elchuru suite. K-Ba and K-Rb correlations vary during the fractionation process, being strongly positive for the early members and almost noncorrelatable for the late fractions. The covariant relation between Ba and Sr is not well developed in any of the suites. Significant positive correlation between Rb and the degree of differentiation has been observed for the Koraput and the Kunavaram suites but not for the Elchuru suite. Liappears to be fractionated with the early mafic phases and is negatively correlated with Na. Zr shows a significant positive correlation with differentiation in the Elchuru but not in the Koraput suite although Ti/Zr falls remarkably with advancing differentiation for both the suites. P and Ti are mutually positively correlated in all the three suites and both tend to manifest significant negative correlation with progressive fractionation. K-(P + Ti + Sr) seems to be a good indicator of the fractionation process in the suites investigated.

    • SP anomaly over doable line of poles-interpretation through log curves

      B V S Murty P Haricharan

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      In the analysis and interpretation ofsp anomalies, two-dimensional finite sheet models are equated to the double line of poles. The profiles over such a model being asymmetric with a minor positive peak and a major negative peak, a double logarithmic curve matching technique simpler than that of Meiser is suggested in the paper for easy and unique solution for all values of depth, dip and length. This technique along with a few others have been tested on two profiles across the sulphide deposit from the Rakha Mines, Singhbhum copper belt, India.

    • Depositional environment of the Krol Group of the Nainital area and its impact on the stromatolites

      S B Misra

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      Depositional environment of the Krol group varied temporally from subtidal in the Manora to intertidal in the Sleepy Hollow times. The conditions that succeeded were peritidal in the Ayarpatta and supratidal in the Narainnagar times. These conditions were the main controlling factors in the growth and development of the algal stromatolites. The Manora formation, due to subtidal conditions, and the Sleepy Hollow formation, due to detrital influx, are almost devoid of stromatolites. The carbonates of the Ayarpatta formation representing a peritidal complex possess columnar and oncolitic stromatolites, while the sediments of the Narainnagar formation characterized by supratidal features contain blistered, domal and crinkled-laminar forms. The types and sizes of stromatolites therefore are governed by the depositional conditions prevailing in the sedimentary basin.

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