A technique for the determination of areal average rainfall / Une méthode pour la détermination de précipitation moyenne pour une zone donnée

Abstract

A method was developed for allocating an area likely to be shared by a raingauge station. Average areal precipitation was found by weighting the rainfall at the gauging station in terms of the product of distances enclosing it or radiating from it. The method was applied to two real and two hypothetical basins and the results were compared with those obtained by existing techniques.     

A GENERALIZED METHOD OF COMPUTING SECOND DERIVATIVE OF GRAVITY FIELD*

The unsuitability of a particular method of computation of second derivative to varying types of field problems evinces the need of a method by which it may be possible to obtain a wide range of filters. This requirement is achieved by incorporating a mathematical smoothing operator, e^-λρ2, λ and ρ being the smoothing parameter and radial frequency respectively, in the theoretical frequency response of second derivative operation. A few sets of weights for various smoothing parameters, are presented. The analysis of Bouguer gravity anomaly map of Los Angeles Basin, California, U.S.A., is carried out by Elkins's (1951) and Rosenbach's (1953) methods and the sets of weights given in this paper which clearly establishes their filtering equivalence.     

P-T-X Relationships Deduced from Corona Textures in Sapphirine--Spinel--Quartz Assemblages from Paderu, Southern India

The sapphirine (Sa)-spinel (Sp)-quartz (Qz)-bearing rocks fromPaderu occur as lenticular enclaves within the Precambrian khondalite-charnockiteterrane of southern India. In addition these rocks contain orthopyroxene(Opx), sillimanite (Sill), garnet (Gt), cordierite (Cd), biotite,potash feldspar (Kf), plagioclase, and symplectites of Cd-Kf-Qz-Opx.The symplectites may have formed from the breakdown of osumilite.Grain contacts of sapphirine and spinel with quartz are rarelyobserved and the incompatibility with quartz during later stagesis displayed by the development of several types of polymineralicreaction coronas. The coronas in the different rock types A,B, etc. are (minerals listed from core to rim of corona): (A-1) sapphirine-bearing rock type without spinel: Sa-Sill-Opx,Sa-Sill-Cd, Sa-Cd-Opx (A-2) sapphirine and spinel-bearing: Sp-Sa-Sill-Opx-Qz, Sp-Sa-Sill,Sp-Sa-Opx, Sp-Sill-Opx, Sp-Sa-Sill-Gt-Qz, Sa-Sill-Opx, Sp-Sa-Sill-Opx,Sa-Sill-Opx-Gt, Sp-Sa-Opx-Gt, Sp-Sa-Sill-Gt; and (B) spinel-bearingbut sapphirine free: Sp-Sill-Opx, Sp-Sill-Gt, Sp-Cd. Commonlythe coronas in the rock type A 2 and B also contain ilmeno-hematite?corundumin the core in association with spinel. These rock types alsoprovide textural evidence for later crystallization of Cd, Cd+ Sa, and Gt + Qz from Opx+Sill?Qz and Gt+Sill+Qz. Sapphirine is aluminous (near 7(Mg, Fe²⁺)O?9(Al, Fe³⁺)₂O₃?3SiO₂)and contains up to 12?2 wt. per cent iron as FeO. Orthopyroxeneis also aluminous, containing up to 10?4 wt. per cent Al₂O₃.Sapphirine and spinel have relatively high contents of Fe₂O₃.X_Mg in the Fe-Mg minerals increases from rock type B to A2 toA1. A sequence of reactions has been deduced from coronas and otherreaction textures, and from the phase compatibility relationsin the FeO-MgO-Al₂O₃-SiO₂-H₂O system. The P-T-X relationshipsfrom geothermobarometry and petrogenetic grids, viz. µ_Fe2O3vs. µ_FeO and µ_H2O vs. µ_Fe2O3, suggest: (1)a retrograde, mildly decompressive trajectory from 900?60?C/65?0?7kb (core) to 760?50?C/5 ? 0?6 kb (rim); and (2) the observedmineralogy of the coronas and reactions deduced from them aredependent on the relative FeO, Fe₂O₃, and H₂O contents of therocks (µ_FeO3, µ_Fe2O3), and µ_H2O).     

Internally consistent recalibrations of mineral equilibria for geothermobarometry involving garnet–orthopyroxene–plagioclase–quartz assemblages and their application to the South Indian granulites

Abstract Three reactions are calibrated as geothermobarometers for garnet–orthopyroxene–plagioclase–quartz assemblages, namely: 1/2 ferrosilite + 1/3 pyrope ± 1/2 enstatite + 1/3 almandine (A): ferrosilite + anorthite ± 2/3 almandine + 1/3 grossularite + quartz (B); and enstatite + anorthite ± 2/3 pyrope + 1/3 grossularite + quartz (C). The internally consistent geothermobarometers based on reactions (A), (B) and (C) are calibrated from experimental data only. The thermodynamic parameters of reaction (A) are derived from published experimental data in the FMAS system (n= 104) in the range 700–1400°C and 5–50 kbar, while those for reaction (B) are derived by summation of the existing reversed experimental data of the mineral equilibria: ferrosilite ± fayalite + quartz (D) and anorthite + fayalite ± 2/3 almandine + 1/3 grossularite (E). The retrieved thermodynamic parameters for reactions (A), (B) and (C) are, respectively: (ΔH⁰, cal) -3367 ± 209, -2749 ± 350 and +3985 ± 545; (ΔS⁰, cal K^?1) -1.634 ± 0.163, -8.644 ± 0.298 and -5.376 ± 0.391; and (ΔV⁰_1,298, cal bar^?1) -0.024, -0.60946 and -0.5614. On a one-cation basis, the derived Margules parameters of the ternary Ca–Fe–Mg in garnet are: W_Fe–Mg= -1256 + 1.0 (～0.23) T(K), W_Mg–Fe= 2880 -1.7 (～0.13) T(K), W_Ca–Mg= 4047 (～77) -1.5 T(K), W_Mg–Ca= 1000 (～77) -1.5 T(K), W_Ca–Fe= -723 + 0.332 (～0.02) T(K), W_Fe–Ca= 1090, (cal) and the ternary constant C₁₂₃= -4498 + 1.516 (～0.265) T(K) cal (subregular solution model of non-ideal mixing); and Fe–Mg–Al in orthopyroxene: W_Fe–Mg= 948 (～200) -0.34 (～0.10) T(K), W_Fe–Al= -1950 (～500) and W_Mg–Al= 0 (cal) (regular solution model of non-ideal mixing). The anorthite activity in plagioclase is calculated by the ‘Al-avoidance’model of subregular Ca–Na mixing commonly used for geobarometry based on reactions (B) and (C). When the geothermobarometers are applied to garnet–orthopyroxene–plagioclase–quartz assemblages (n= 45) of wide compositional range from the Precambrian South Indian granulites, temperature ranges of 690–860°C (X= 760 ± 45°C) and pressure ranges of 5–10 kbar were obtained. The P–T values were estimated simultaneously and there is no difference in the pressure calculated from P_Mg (reaction C) and P_Fe (reaction B). In the existing calibrations this difference is 1 kbar or more. Furthermore, there is no compositional dependence of the ln K of the experimental data in the FMAS (n= 104) and the CFMAS (n= 78) systems at different temperatures and the estimated temperatures of the South Indian granulites.     

Drought flow analysis of the River Tigris at Baghdad / Analyse d'écoulement pendant les séchéresses pour le Tigre à Baghdad

Abstract

Some commonly used statistical distributions have been compared to find their applicability for describing minimum flows of the Tigris River at Baghdad gauging station. Drought flows with given return period have, thereafter, been predicted by these techniques. The mean of the estimated flows by the various distributions has been calculated to represent a design drought; upper and lower values estimated have been used to give an idea of variation in drought flow estimation. The methodology suggested herein may avoid the dilemma as to which distribution to select for drought flow estimation.     

CALCULATION OF THE VERTICAL GRADIENT OF THE GRAVITY FIELD USING THE FOURIER TRANSFORM*

Fourier transform techniques have been used to calculate the theoretical filter (amplitude) response function of Nth order vertical derivative continuation operation. The amplitude response functions of the vertical gradient and its continuation follow from the same. These response functions are subsequently used to calculate the weighting coefficients suitable for two dimensional equispaced data. A shortening operator has been incorporated to limit the extent of the operator. For comparative study, some of the developed coefficient sets and the one presented in this paper are analysed in the frequency domain and their merits and demerits are discussed.