Precipitable water and dew point temperature relationship during the Indian summer monsoon     

Sinha  Subroto  Sinha  Sushanta K. 《Pure and Applied Geophysics》1981,119(5):913-921

Two years of contrasting monsoon rainfall over the Indian subcontinent are studied with reference to (a) total precipitable water and precipitation efficiencies during the respective years and (b) the correlation between the dew point temperature at a particular level and the total precipitable water. It is found that the maximum correlation occurs between the dew point temperature at the 850 mb level and the total precipitable water at an individual station. The precipitation efficiencies are less during the year of bad monsoon. A linear regression equation is attempted between the total precipitable water and dew point temperature.  相似文献   

Shift of quasi-stationary flow features during active and break monsoons     

R N Keshavamurty  V Satyan  S K Dash  H S S Sinha 《Journal of Earth System Science》1980,89(2):209-214

During our search for dynamical differences in monsoon flows between the active and break phases of the monsoon, we noticed some interesting differences which may have some dynamical significance and do not appear to have been highlighted so far. There appear to be shifts of quasi-stationary flow features both in the lower and upper tropospheres.  相似文献   

Comparative geochronology in the reversely zoned plutons of the Bottle Lake Complex,Maine: U-Pb on zircons and Rb-Sr on whole rocks     

R. A. Ayuso  J. G. Arth  A. K. Sinha  J. Carlson  D. R. Wones 《Contributions to Mineralogy and Petrology》1984,88(1-2):113-125

The Bottle Lake Complex is a composite granitic batholith emplaced into Cambrian to Lower Devonian metasedimentary rocks. Both plutons (Whitney Cove and Passadumkeag River) are very coarse grained hornblende and biotite-bearing granites showing petrographic and geochemical reverse zonation. Two linear whole rock Rb/Sr isochrons on xenolith-free Whitney Cove and Passadumkeag River samples indicate ages of 379±5 m.y. and 381±4 m.y., respectively, in close agreement with published K-Ar ages for biotite from Whitney Cove of 377 m.y. and 379 m.y., and for hornblende ⁴⁰Ar/³⁹Ar determinations from Passadumkeag River which indicate an age of 378±4 m.y. The initial Sr isotopic ratio for Whitney Cove is 0.70553 and for Passadumkeag River is 0.70414. A whole-rock isochron on a suite of xenoliths from the Passadumkeag River granite indicates a whole rock Rb-Sr age of 496±14 m.y., with an initial Sr isotopic ratio of 0.70262.Two types of zircon exhibiting wide petrographic diversity are evident in variable proportions throughout the batholith. One of these types is preferentially found in a mafic xenolith and it is widely dispersed in the host granites forming discrete grains and probably as inclusions in the other type of zircon. U-Pb analyses of zircons give concordia intercept ages of 399±8 m.y. for Whitney Cove, 388±6 m.y. for Passadumkeag River, 415 m.y. for a mafic xenolith in Passadumkeag River, and 396±32 for combined Whitney Cove and Passadumkeag River granite. The zircons show a spread of up to 20 m.y. in the ²⁰⁷Pb/²⁰⁶Pb ages. Omitting the finest zircon fraction in the Passadumkeag River results in a concordia intercept age of 381±3 m.y., in better agreement with the whole-rock Rb-Sr and mineral K-Ar ages. For the Whitney Cove pluton, exclusion of the finest fraction does not bring the zircon age into agreement with the Rb-Sr data.Age estimates by the whole rock Rb-Sr, mineral K-Ar and Ar-Ar methods suggest that the crystallization age of the plutons is about 380 m.y., slightly younger than the U-Pb zircon intercept ages. A possible reason for this discrepancy is that the zircons contain inherited lead. Thus, zircon U-Pb ages might represent a mixture of newly developed zircon and older inherited zircon, whereas the Rb-Sr whole rock age (380 m.y.) reflects the time of crystallization, and the argon ages result from rapid cooling after emplacement.  相似文献   

Geochemical and strontium isotopic characteristics of parental Aleutian arc magmas: evidence from the basaltic lavas of Atka   总被引：3，自引：1，他引：3  

James D. Myers  Bruce D. Marsh  A. Krishna Sinha 《Contributions to Mineralogy and Petrology》1986,94(1):1-11

Eighteen flows from a basal stratigraphic sequence on the Aleutian Island of Atka were analyzed for major elements, trace elements and initial ⁸⁷Sr/⁸⁶Sr ratios. Petrographically, these lavas contain abundant plagioclase (24–45%) and lesser amounts of olivine (<7%), magnetite and clinopyroxene phenocrysts. Compositionally, the lavas are high-alumina (20wt%) basalts (48–51 wt% SiO₂) with low TiO₂ (<1%) and MgO (<5%). Within the section, compositional variations for all major elements are quite small. While MgO content correlates with olivine phenocryst contents, no such relationship exists between the other oxides and phenocryst content. These lavas are characterized by 8–10 ppm Rb, high Sr (610–669 ppm), 308–348 ppm Ba and very constant Zr (23–29 ppm) and Sc (23–29 ppm) abundances. Ni and Cr display extremely large compositional ranges, 12–118 ppm and 12–213 ppm, respectively. No correlation exists between trace element concentrations and phenocryst contents. Strontium isotopic ratios show a small but significant range (0.70314–0.70345) and are slightly elevated with respect to typical MORB. No systematic correlation between stratigraphic position and petrography or geochemistry is evident. REE abundances measured on six samples are LREE enriched ((La/ Yb)_N = 2.20–2.81) and display similar chondrite normalized patterns. One sample has a slight positive Eu anomaly but the other lavas do not. Compared to other Aleutian basalts of similar silica content, these lavas are less LREE enriched and have lower overall abundances. The geochemical characteristics of these basalts suggest they represent true liquid compositions despite their highly porphyritic nature. Published phase relations indicate fractionation of a more MgO-rich magma could not have produced these lavas. The high Al₂O₃ and low MgO and compatible element abundances suggest a predominantly oceanic crustal source for parental high-alumina basalts.  相似文献   

Geochemical problems associated with deccan basalts     

R. C. Sinha 《Bulletin of Volcanology》1971,35(4):1015-1021

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Propagation of elastic waves in an infinite plate of transversely isotropic material in three dimensions     

Nirmal Kumar Sinha 《Pure and Applied Geophysics》1971,86(1):80-87

Summary Free oscillations in three dimensions of an infinite plate of transversely isotropic material are studied in this paper. The dependence of the wave-velocity on the frequency has been determined numerically for the first two modes of propagation only and plotted graphically.  相似文献   

On plane waves in thermo-viscoelastic solids deformed by magnetic fields     

Dilip K. Sinha 《Pure and Applied Geophysics》1964,57(1):53-60

Summary In the present paper,Maxwell's electromagnetic equations together with the equation of motion of two types of viscoelastic solids have been used to deal with the propagation of magneto-thermoviscoelastic plane waves.  相似文献   

Effect of atmospheric gases,surface albedo and cloud overlap on the absorbed solar radiation     

Ashok Sinha 《Annales Geophysicae》1996,14(3):329-335

Recent studies have provided new evidence that models may systematically underestimate cloud solar absorption compared to observations. This study extends previous work on this “absorption anomaly” by using observational data together with solar radiative transfer parameterisations to calculate f_s (the ratio of surface and top of the atmosphere net cloud forcings) and its latitudinal variation for a range of cloud types. Principally, it is found that (a) the zonal mean behaviour of f_s varies substantially with cloud type, with the highest values obtained for low clouds; (b) gaseous absorption and scattering can radically alter the pattern of the variation of f_s with latitude, but gaseous effects cannot in general raise f_s to the level of around 1.5 as recently determined; (c) the importance of the gaseous contribution to the atmospheric ASR is such that whilst f_s rises with surface albedo, the net cloud contribution to the atmospheric ASR falls; (d) the assumed form of the degree of cloud overlap in the model can substantially affect the cloud contribution to the atmospheric ASR whilst leaving the parameter f_s largely unaffected; (e) even large uncertainties in the observed optical depths alone cannot account for discrepancies apparent between modelled and newly observed cloud solar absorption. It is concluded that the main source of the anomaly may derive from the considerable uncertainties regarding impure droplet microphysics rather than, or together with, uncertainties in macroscopic quantities. Further, variable surface albedos and gaseous effects may limit the use of contemporaneous satellite and ground-based measurements to infer the cloud solar absorption from the parameter f_s.  相似文献   

Urban Ground Water Pollution: A Case Study in Cuttack City, India     

Jyotirmaya Das  Rama Krishna Sahoo  B.K. Sinha 《Ground Water Monitoring & Remediation》2002,22(3):95-103

A large number of ground water samples (360) was collected from 60 stations over six consecutive seasons to study the influence of the main sewerage drain on shallow ground water table beneath the municipal area of Cuttack, India. A majority of the samples collected from stations close to the drain exceeded the maximum permissible limits set by the World Health Organization (WHO). Almost all the samples near the drain exceeded the WHO limit for NO₃^- and Na⁺. However, the concentrations decreased as the distance from the drain increased. The winter season registered the maximum concentrations of NH₄⁺, NO₃^-, and SO₄^2- ions whereas the minimum values always coincided with the rainy season. R-mode factor analysis was conducted to find relationships amongst the 16 chemical parameters studied. Fluoride showed a negative correlation with Cl^-, Na⁺, NO₃^-, SO₄^2-, and PO₄^3-. The concentration of F^- may be lower in raw waste water than naturally occurs in the ground water. Therefore, a decrease in the concentration of F^- near the drain may be attributed to dilution by contributions of waste water to the ground water. The rest of the parameters were found to be directly related to the distance of collection points to the sewerage. The distribution of nutrients is strongly affected by leaching of waste water into the ground water.  相似文献   

Sensitivity and inversion of borehole flexural dispersions for formation parameters     

Bikash K. Sinha 《Geophysical Journal International》1997,128(1):84-96

Propagation characteristics of borehole flexural waves are functions of five borehole, fluid and formation parameters. Uncertainties in any of these model parameters may introduce errors in the estimate of formation shear-wave speed. Other sources of error in the estimate may be caused by deviations from the assumed circular borehole cross-section or heterogeneity in the material properties of formation in the vicinity of a borehole from the usually assumed homogeneous properties. The influence of uncertainties in model parameters on borehole flexural dispersion has been calculated from a general perturbation model based on Hamilton's principle. A sensitivity analysis of the flexural dispersion to small variations in the model parameters shows that the formation shear speed has by far the most dominant influence in a slow formation. In contrast, the flexural dispersion in a fast formation is significantly influenced by three of the five model parameters: the formation shear speed, the borehole fluid compressional speed and the borehole diameter. The frequency dependence of these sensitivity functions indicates that the inversion of flexural dispersion for formation shear speed is optimal in the range 2–4 kHz for a borehole of diameter 25.4 cm. The range of validity of the perturbation model has been estimated by comparing results of concentric annuli of different thicknesses, and shear-wave speeds different from that of the formation with those from exact numerical solutions from a modal search program. Generally, the perturbation results for altered annuli of thicknesses up to 15 cm are accurate to within 1 per cent for a shear-wave speed 10 per cent lower than that of the formation. This difference between the perturbation and exact results increases to approximately 1 to 3 per cent for a shear-wave speed 20 per cent lower than that of the formation.  相似文献