Hydrometeorological processes in semi-arid western India: insights from long term isotope record of daily precipitation     

Harsh Oza  Virendra Padhya  Akash Ganguly  K. Saikranthi  T. N. Rao  R. D. Deshpande 《Climate Dynamics》2020,54(5):2745-2757

Long term (2005–2016) daily precipitation isotope data (δ18O, δD and d-excess) from Ahmedabad in semi-arid Western India are examined in light of various meteorological parameters and air parcel trajectories to identify prominent patterns in the isotopic character and discern the underlying hydrometeorological processes. One of the most prominent and systematic annual patterns is the isotopic depletion (average δ18O: − 2.5‰ in Jun–Jul; − 5.2‰ in Aug–Sept) in the second half of the Indian Summer Monsoon (ISM), which is observed in the 11 out of the 12 years of this study. Four geographically feasible causal factors have been examined if they contribute to observed late monsoon isotopic depletion. These factors are: (1) increased contribution of terrestrially recycled vapor; (2) intra-seasonal change in sea-surface, surface-air and cloud base temperatures; (3) increased rain-out fraction from marine vapor parcel; and (4) increase in relative proportion of convective rain. It is inferred from the present study that isotopic depletion in the second half of ISM is associated with: (1) increased contribution (45% from 36%) of terrestrially recycled moisture; (2) 1.9° C lower cloud base temperature; (3) increased rainout fraction due to decreased wind velocity (6.9 m/s from 8.8 m/s); and (4) an increase of 22.3% in the proportion of convective rain. Daily rain events with atypical isotopic composition (20‰ < d-excess < 0‰) are ascribed mainly to local weather perturbations causing sudden updraft of moist air facilitating terrestrial recycling of water vapor.  相似文献   

Comparison of Monsoonal change of water quality parameters between 1983 and 2008 in a tropical estuary in Northeastern India: role of phytoplankton and community metabolism     

Mitali Dey  Chumki Chowdhury  Asim A. Pattnaik  Dipnarayan Ganguly  Sandip K. Mukhopadhyay  Tarun K. De  Tapan K. Jana 《Marine Ecology》2013,34(1):14-29

Ongoing climate change and anthropogenic activities are introducing stressors that affect the structure and function of coastal ecosystems. This paper focuses on the fluvial fluxes and estuarine transport of nutrients from a tropical river (Mahanadi River) in Northeastern India and compares select nutrient and water quality parameters between 1983 and 2008. This estuary acts as a perennial source of CO₂ with a net annual flux to the atmosphere of about 135 tons. The non‐conservative fluxes showed a net annual removal of 650 and 140 tons of phosphorus and nitrogen from the water column, respectively. Negative biogeochemical feedbacks that decreased the availability of N and P in 2008 relative to 1983 levels indicate major changes in biogeochemical responses towards fluvial fluxes of nutrient.  相似文献   

Regional and seasonal intercomparison of CMIP3 and CMIP5 climate model ensembles for temperature and precipitation   总被引：2，自引：1，他引：1  

Devashish Kumar  Evan Kodra  Auroop R. Ganguly 《Climate Dynamics》2014,43(9-10):2491-2518

Regional and seasonal temperature and precipitation over land are compared across two generations of global climate model ensembles, specifically, CMIP5 and CMIP3, through historical twentieth century skills and multi-model agreement, and twenty first century projections. A suite of diagnostic and performance metrics, ranging from spatial bias or model-consensus maps and aggregate time series plots, to measures of equivalence between probability density functions and Taylor diagrams, are used for the intercomparisons. Pairwise and multi-model ensemble comparisons were performed for 11 models, which were selected based on data availability and resolutions. Results suggest little change in the central tendency or variability or uncertainty of historical skills or consensus across the two generations of models. However, there are regions and seasons, at different levels of aggregation, where significant changes, performance improvements, and even degradation in skills, are suggested. The insights may provide directions for further improvements in next generations of climate models, and in the meantime, help inform adaptation and policy.  相似文献   

Adsorption kinetic control of As(III &; V) mobilization and sequestration by Mangrove sediment     

S. K. Mandal  N. Majumder  C. Chowdhury  D. Ganguly  M. Dey  T. K. Jana 《Environmental Earth Sciences》2012,65(7):2027-2036

Elevated concentrations of arsenic in the sediment and pore water in the Sundarban wetlands pose an environmental risk. Adsorption and desorption are hypothesized to be the major processes controlling arsenic retention in surface sediment under oxic/suboxic condition. This study aims to investigate sorption kinetics of As(III & V) and its feedback to arsenic mobilization in the mangrove sediment. It ranges from sand to silty clay loam and shows the adsorption of As(III & V) following the Langmuir relation. Estimates of the maximum adsorption capacity are 59.11 ± 13.26 μg g⁻¹ for As(III) and 58.45 ± 8.75 μg g⁻¹ at 30°C for As(V) in the pH range 4 to 8 and salinity 15–30 psu. Extent of adsorption decreases with increasing pH from 4 to 8 and desorption is the rate-limiting step in the reaction of arsenic with sediment. Arsenic in the sediment could be from a Himalayan supply and co-deposited organic matter drives its release from the sediment. Arsenic concentration in the sediment is well below its maximum absorption capacity, suggesting the release of sorbed arsenic in pore water by the microbial oxidation of organic matter in the sediment with less feedback of adsorption.  相似文献   

Geothermal reservoirs — A brief review   总被引：1，自引：0，他引：1  

Sayantan Ganguly  M. S. Mohan Kumar 《Journal of the Geological Society of India》2012,79(6):589-602

A brief discussion and review of the geothermal reservoir systems, geothermal energy and modeling and simulation of the geothermal reservoirs has been presented here. Different types of geothermal reservoirs and their governing equations have been discussed first. The conceptual and numerical modeling along with the representation of flow though fractured media, some issues related to non isothermal flow through fractured media, the efficiency of the geothermal reservoir, structure of the numerical models, boundary conditions and calibration procedures have been illustrated. A brief picture of the Indian scenario and some barriers related with geothermal power are discussed and presented thereafter. Finally some gaps of the existing knowledge and recent focuses of research are discussed.  相似文献   

Cr diffusion in orthopyroxene: Experimental determination, Mn-Cr thermochronology, and planetary applications     

Jibamitra Ganguly  Motoo Ito  Xiaoyu Zhang 《Geochimica et cosmochimica acta》2007,71(15):3915-3925

We have determined Cr diffusion coefficients (D) in orthopyroxene parallel to the a-, b-, and c-axial directions as a function temperature at f(O₂) corresponding to those of the wüstite-iron (WI) buffer. Diffusion is found to be significantly anisotropic with D(//c) > D(//b) > D(//a), conforming to an earlier theoretical prediction. Increase of f(O₂) from WI buffer conditions to 4.5 log unit above the buffer at 950 and 1050 °C leads to decrease of D(Cr) by a factor of two to three, possibly suggesting significant contribution from an interstitial diffusion mechanism. We have used the diffusion data to calculate the closure temperatures (T_c) of the Mn-Cr decay system in orthopyroxene as a function of initial temperature (T₀), grain size (a) and cooling rate for spherical and plane sheet geometries. We also present graphical relations that permit retrieval of cooling rates from knowledge of the resetting of Mn-Cr ages in orthopyroxene during cooling, T₀ and a. Application of these relations to the Mn-Cr age data of the cumulate eucrite Serra de Magé yields a T_c of 830-980 °C, and cooling rates of 2-27 °C/Myr at T_c and ∼1-13 °C/Myr at 500 °C. It is shown that the cooling of Serra de Magé to the closure temperature of the Mn-Cr system took place at its original site in the parent body, and thus implies a thickness for the eucrite crust in the commonly accepted HED parent body, Vesta, of greater than 30 km. This thickness of the eucrite crust is compatible only with a model of relatively olivine-poor bulk mineralogy in which olivine constitutes 19.7% of the total asteroidal mass.  相似文献   

Rare earth diffusion kinetics in garnet: Experimental studies and applications     

Massimiliano Tirone  Jibamitra Ganguly  Ralf Dohmen  Richard Hervig 《Geochimica et cosmochimica acta》2005,69(9):2385-2398

We determined the diffusion coefficient of Sm in almandine garnet as function of temperature at 1 bar and fO₂ corresponding to that of wüstite-iron buffer, and to a limited extent, that of a few other selected rare earth elements in almandine and pyrope garnets. Both garnets were demonstrated to have metastably survived the diffusion annealing at conditions beyond their stability fields. The experimental diffusion profiles were analyzed by secondary ion mass spectrometry, and in addition, by Rutherford back scattering spectroscopy for two samples. Transmission electron microscopic study of an almandine crystal that was diffusion-annealed did not reveal any near-surface fast diffusion path. Using reasonable approximations and theoretical analysis of vacancy diffusion, the experimental data were used to develop an expression of rare earth element (REE) diffusion coefficient in garnet as a function of temperature, pressure, fO₂, ionic radius, and matrix composition. Calculation of the closure temperature for the Sm-Nd decay system in almandine garnet in a metamorphic terrain shows very good agreement with that constrained independently. Modeling of the REE evolution in melt and residual garnet suggests that for dry melting condition, the REE pattern in the melt should commonly conform closely to that expected for equilibrium melting. However, for much lower solidus temperatures that would prevail in the presence of a H₂O-CO₂ fluid, the concentration of light REE in the melt could be significantly lower than that under equilibrium melting condition. A reported core and rim differences in the REE content of a garnet crystal in a mantle xenolith in kimberlite have been reproduced by assuming that the REE zoning was a consequence of entrapment in a magma derived from an external source for ∼32,000 yr before the eruption.  相似文献   

Are Majhgawan-Hinota pipe rocks truly group-I Kimberlite?     

Ravi Shanker  S. Nag  A. Ganguly  A. Absar  B. P. Rawat  G. S. Singh 《Journal of Earth System Science》2001,110(1):63-76

The diamond bearing pipe rocks in Majhgawan-Hinota (more than four pipes) occur as intrusives in sandstones of Kaimur Group. These Proterozoic (974 ±30-1170 ±20 Ma) intrusive rocks, occupying the southeastern margin of Aravalli craton, were called as ‘micaceous kimberlite’ in tune with the reported kimberlite occurrences from other parts of the world. Judging from the definition of kimberlite, as approved by the IUGS Subcommission on Systematics of Igneous Rocks, it is not justified to call these rocks as ‘micaceous kimberlite’. Rather the mineralogical assemblages such as absence of typomorphic mineral monticellite (primary), abundance of phlogopite cognate, frequent presence of barite and primary carbonate mostly as calcite coupled with ultrapotassic and volatile-rich (dominantly H₂O) nature and high concentration of incompatible elements (such as Ba, Zr, Th, U), low Th/U ratios, low REE and no Eu-anomaly clearly indicate a close similarity with that of South African orangeites. Thus orangeites of Proterozoic age occur outside the Kaapvaal craton of South Africa which are much younger (200 Ma to 110 Ma) in age.  相似文献   

Groundwater flow in an arsenic-contaminated aquifer,Mekong Delta,Cambodia     

Shawn G. Benner  Matthew L. Polizzotto  Benjamin D. Kocar  Somenath Ganguly  Kongkea Phan  Kagna Ouch  Michael Sampson  Scott Fendorf 《Applied Geochemistry》2008

To advance understanding of hydrological influences on As concentrations within groundwaters of Southeast Asia, the flow system of an As-rich aquifer on the Mekong Delta in Cambodia where flow patterns have not been disturbed by irrigation well pumping was examined. Monitoring of water levels in a network of installed wells, extending over a 50 km² area, indicates that groundwater flow is dominated by seasonally-variable gradients developed between the river and the inland wetland basins. While the gradient inverts annually, net groundwater flow is from the wetlands to the river. Hydraulic parameters of the aquifer (K ≈ 10⁻⁴ ms⁻¹) and overlying clay aquitard (K ≈ 10⁻⁸ ms⁻¹) were determined using grain size, permeameter and slug test analyses; when coupled with observed gradients, they indicate a net groundwater flow velocity of 0.04–0.4 ma⁻¹ downward through the clay and 1–13 ma⁻¹ horizontally within the sand aquifer, producing aquifer residence times on the order 100–1000 a. The results of numerical modeling support this conceptual model of the flow system and, when integrated with observed spatial trends in dissolved As concentrations, reveal that the shallow sediments (upper 2–10 m of fine-grained material) are an important source of As to the underlying aquifer.  相似文献   

Hydromagnetic stability of some non-dissipative flows subject to non-axisymmetric disturbances     

S. N. Bhattacharyya  A. S. Gupta  K. Ganguly 《Astrophysics and Space Science》1985,115(1):51-60

We study the linear stability of nondissipative flow of an electrically conducting fluid subject to non-axisymmetric disturbances in the following cases: (i) the radial flow of an incompressible fluid between two concentric porous circular cylinders in the presence of a radial magnetic field and (ii) axial flow of a compressible fluid between two concentric circular cylinders permeated by a helical magnetic field (0,B ₀(r),B _0z) in a cylindrical coordinate system. It is shown that in case (i), the flow is stable if the Alfvén velocity based on the undisturbed radial magnetic field exceeds the radial velocity due to suction or injection at the cylinder surfaces. In case (ii), it is found that under certain conditions the complex wave speed for an unstable mode lies within a circle of diameterW _max-W _min, whereW _max andW _min are the maximum and minimum values of the axial velocity in the flow region. In the presence of a purely axial magnetic field, however, the complex wave speed for an unstable mode always lies within the above circle.  相似文献