Petrology, geothermobarometry and C-O-H-S fluid compositions in the environs of Rampura-Agucha Zn-(Pb) ore deposit, Bhilwara District, Rajasthan

The massive Zn-(Pb) sulfide ore body at Rampura-Agucha in Bhilwara district, Rajasthan, occurs within graphitic metapelites surrounded by garnet-biotite-sillimanite gneiss containing concordant bodies of amphibolite. These rocks and the sulfide ores have been studied to estimate the pressure, temperature and fluid composition associated with upper amphibolite facies metamorphism. Geothermobarometric calculations involving garnet-biotite and garnet-hornblende pairs, as well as sphalerite-hexagonal pyrrhotite-pyrite and garnet-plagioclase-sillimanite-quartz assemblages indicate that the most pervasive P-T condition during peak of regional metamorphism was 650°C and 6 kb, and was attained between the first and second deformations in the region. Some temperature-pressure estimates also cluster around 500°C–5.1 kb which probably represent retrograde cooling during unloading. Consideration of devolatilization equilibria in the C-O-H-S system at the pervasive metamorphic conditions mentioned above shows that the metamorphic fluid was H₂O-rich ( ) but also had a substantial component of . and were the other important phases in the fluid. CO (X_CO = 0.002) and were the minor phases in the fluid. It is probable that a part of this aqueous fluid was consumed by re-/neocrystallization of hydrous silicate phases like chlorite during the retrogressive metamorphic path, so that fluid entrapped in quartz below 450°C was rendered CO₂-rich (Holleret al 1996).     

Hydrogeochemical evaluation and statistical analysis of groundwater of Sylhet,north-eastern Bangladesh

Acta Geochimica - To investigate the hydrogeochemical characteristics of groundwater 23 shallow, 30 intermediate and 38 deep wells samples were collected from Sylhet district of Bangladesh, and...     

Response of multilayer geosynthetic-reinforced bed resting on soft soil with stone columns

In the present study, a mechanical model has been developed to study the behavior of multilayer geosynthetic-reinforced granular fill over stone column-reinforced soft soil. The granular fill and geosynthetic reinforcement layers have been idealized by Pasternak shear layer and rough elastic membranes, respectively. The Kelvin–Voight model has been used to represent the time-dependent behavior of saturated soft soil. The stone columns are idealized by stiffer springs and assumed to be linearly elastic. The nonlinear behavior of the soft soil and granular fill is considered. The effect of consolidation of soft soil due to inclusion of the stone columns on settlement response has also been included in the model. Plane strain conditions are considered for the loading and reinforced foundation soil system. An iterative finite difference scheme is applied for obtaining the solution and results are presented in nondimensional form. It has been observed that if the soft soil is improved with stone columns, the multilayer reinforcement system is less effective as compared to single layer reinforcement to reduce the total settlement as there is considerable reduction in the total settlement due to stone column itself. Multilayer reinforcement system is effective for reducing the total settlement when stone columns are not used. However, multilayer reinforcement system is effective to transfer the stress from soil to stone column. The differential settlement is also slightly reduced due to application of multiple geosynthetic layers as compared to the single layer reinforcement system.     

Radon as seismic precursor: new data with well water of Jalpaiguri,India

This paper reports the measurement of radon concentration in well water at the site of Jalpaiguri (26°32′N, 88°46′E) near the active fault zone of West Bengal, India. Radon concentration has been measured in well water with the help of solid-state nuclear track detectors (SSNTD). The study indicates a positive correlation between radon anomaly and earthquake. The data of radon content in well water have been compared with that in soil gas at the same site.     

Sensitivity of Indian Monsoon to Entrainment and Detrainment in Mass Flux Schemes

A new analytical formulation of entrainment and detrainment in the Tiedtke's mass flux cumulus parameterization is presented here in which cloud height is one of the key parameters. The proposed analytical profiles of entrainment and detrainment are tested in GCM for long-term simulation and are evaluated in the light of the results from the original Tiedtke's scheme and another mass flux scheme due to Emanuel. The variations of Indian monsoon rainfall have been examined with these schemes in a general circulation model. Evaluation of the simulated rainfall against observations is done by empirical orthogonal function (EOF) analysis for the Indian Monsoon region. It is noted that the spatial and temporal variations of the all-India monsoon rainfall are sensitive to the formulation of entrainment and detrainment in a mass flux scheme, and that the new formulation can effectively represent the increased dilution with height in deep clouds.     

4D-variational assimilation over the Bay of Bengal using the Adjoint of a Variable Resolution Global Ocean Model

Summary The adjoint technique has been widely used over the last two decades in applications involving the dynamics of the Atmosphere and Ocean. This present study applies this technique in the assimilation of oceanic parameters such as temperature and net-surface heat flux, in a variable resolution Ocean General Circulation Model (OGCM). The National Center for Environmental Prediction (NCEP) 1999 July–August global data (sea-surface temperature and derived surface heat flux) and vertical temperature profiles collected from ORV Sagar Kanya and INS Sagardhwani during the Bay of Bengal Monsoon Experiment (BOBMEX 1999) are used for assimilation over the Bay of Bengal. The net-surface heat flux and temperature obtained after assimilation show good agreement with their respective seasonal patterns over the whole Indian Ocean, though there are some differences in the numerical values of heat fluxes. The vertical profiles of temperature after assimilation over the Bay of Bengal show strong resemblance with the corresponding ship observations, emphasizing the importance of the adjoint technique in ocean data assimilation.     

Impact of assimilation of INSAT-3D retrieved atmospheric motion vectors on short-range forecast of summer monsoon 2014 over the South Asian region

The Weather Research and Forecasting (WRF) model and its three-dimensional variational data assimilation system are used in this study to assimilate the INSAT-3D, a recently launched Indian geostationary meteorological satellite derived from atmospheric motion vectors (AMVs) over the South Asian region during peak Indian summer monsoon month (i.e., July 2014). A total of four experiments were performed daily with and without assimilation of INSAT-3D-derived AMVs and the other AMVs available through Global Telecommunication System (GTS) for the entire month of July 2014. Before assimilating these newly derived INSAT-3D AMVs in the numerical model, a preliminary evaluation of these AMVs is performed with National Centers for Environmental Prediction (NCEP) final model analyses. The preliminary validation results show that root-mean-square vector difference (RMSVD) for INSAT-3D AMVs is ～3.95, 6.66, and 5.65 ms^?1 at low, mid, and high levels, respectively, and slightly more RMSVDs are noticed in GTS AMVs (～4.0, 8.01, and 6.43 ms^?1 at low, mid, and high levels, respectively). The assimilation of AMVs has improved the WRF model of produced wind speed, temperature, and moisture analyses as well as subsequent model forecasts over the Indian Ocean, Arabian Sea, Australia, and South Africa. Slightly more improvements are noticed in the experiment where only the INSAT-3D AMVs are assimilated compared to the experiment where only GTS AMVs are assimilated. The results also show improvement in rainfall predictions over the Indian region after AMV assimilation. Overall, the assimilation of INSAT-3D AMVs improved the WRF model short-range predictions over the South Asian region as compared to control experiments.     

Evaluation of rainfall–runoff model performance under non-stationary hydroclimatic conditions

ABSTRACT

Understanding of rainfall–runoff model performance under non-stationary hydroclimatic conditions is limited. This study compared lumped (IHACRES), semi-distributed (HEC-HMS) and fully-distributed (SWATgrid) hydrological models to determine which most realistically simulates runoff in catchments where non-stationarity in rainfall–runoff relationships exists. The models were calibrated and validated under different hydroclimatic conditions (Average, Wet and Dry) for two heterogeneous catchments in southeast Australia (SEA). SWATgrid realistically simulates runoff in the smaller catchment under most hydroclimatic conditions but fails when the model is calibrated in Dry conditions and validated in Wet. All three models perform poorly in the larger catchment irrespective of hydroclimatic conditions. This highlights the need for more research aimed at improving the ability of hydrological models to realistically incorporate the physical processes causing non-stationarity in rainfall–runoff relationships. Although the study is focussed on SEA, the insights gained are useful for all regions which experience large hydroclimatic variability and multi-year/decadal droughts.     

Planar and nonplanar ion acoustic shock waves with nonthermal electrons and positrons

The nonlinear propagation of ion acoustic shock waves (IASWs) are studied in an unmagnetized plasma consisting of nonthermal electrons, nonthermal positrons, and singly charged adiabatically hot positive ions, whose dynamics is governed by the two dimensional nonplanar Kadomstev-Petviashvili-Burgers (KPB) equation. The shock solution of the KPB equations is obtained numerically. The effects of several parameters and ion kinematic viscosities on the properties of ion acoustic shock waves are discussed in planar and nonplanar geometry. It is shown that the ion acoustic shock wave propagating in cylindrical/spherical geometry with transverse perturbation will be deformed as time goes on. Also, it is seen that the strength and the steepness of the IASWs increases with increasing β, the nonthermal parameter.