Kinematics of the Gondwana basins of peninsular India

The Gondwana successions (1–4 km thick) of peninsular India accumulated in a number of discrete basins during Permo-Triassic period. The basins are typically bounded by faults that developed along Precambrian lineaments during deposition, as well as affected by intrabasinal faults indicating fault-controlled synsedimentary subsidence. The patterns of the intrabasinal faults and their relationships with the respective basin-bounding faults represent both extensional and strike-slip regimes. Field evidence suggests that preferential subsidence in locales of differently oriented discontinuities in the Precambrian basement led to development of Gondwana basins with varying, but mutually compatible, kinematics during a bulk motion, grossly along the present-day E–W direction. The kinematic disparity of the individual basins resulted due to different relative orientations of the basement discontinuities and is illustrated with the help of a simple sandbox model. The regional E–W motion was accommodated by strike-slip motion on the transcontinental fault in the north.     

A new approach to verify the model core with idealized experiments

Summary ?A newly developed ocean general circulation model has been tested and verified with some idealized experiments. Generally two types of idealized experiments have been done here. First types are called as “symmetric experiments” and second types are called as “transport experiments”. The first types of experiment help to correct the model core and any deficiency from boundary conditions. The second types of experiment are the type of validation experiment. In both the experiments there are no continents, so in the first type of experiments where symmetric forcings are provided one can expect that model should maintain the symmetric nature. In the second type of experiments one can expect that model should respond correctly to the wind forcings, if no wind curl is present in the wind forcing there will be no circulation in the extratropics and if there is no wind the equator there will be no circulation. The model reproduces the possible envisaged results of these experiments and gives the confidence for performing the realistic integration. Received February 20, 2002; accepted July 7, 2002 Published online: February 20, 2003     

A coupled model study on ENSO, MJO and Indian summer monsoon rainfall relationships

Summary In this paper, we have tried to understand the ENSO, MJO and Indian summer monsoon rainfall relationships from observation as well as from coupled model results. It was the general feeling that El-Niño years are the deficient in Indian monsoon rainfall and converse being the case for the La-Niña years. Recent papers by several authors noted the failure of this relationship. We find that the model output does confirm a breakdown of this relationship. In this study we have seen that a statistically defined modified Indian summer monsoon rainfall (MISMR) index, a linearly regressed ISMR index and dynamical Webster index (WBSI), shows an inverse relationship with ENSO index during the entire period of integration (1987 to 1999). It is also seen from this study that the amplification of the MJO signals were large and the ENSO signals were less pronounced during the years of above normal ISMR. The MJO signal amplitudes were small and ENSO signals were strong during the years of deficient ISMR. It has been noted that here is a time lag between the MJO and ENSO signal in terms of their modulation aspect. If time lag is added with the ENSO signal then both signals maintain the amplitude modulation theory. A hypothesis is being proposed here to define a relationship between MJO and ENSO signals for the entire period between 1987 and 1999.Received September 18, 2002; revised November 22, 2002; accepted December 20, 2002 Published online: May 8, 2003     

Mg tracer diffusion in aluminosilicate garnets at 750-850° C, 1 atm. and 1300° C, 8.5 GPa

 Tracer diffusion coefficients of Mg in natural aluminosilicate garnets of composition Alm₃₈Pyr₅₀Gr₁₀Sp₂ and Alm₇₃Pyr₂₁Gr₅Sp₁ have been measured at 1 bar, 750-850° C and at 8.5 GPa, 1300° C by chemically depositing a salt layer enriched in ²⁶Mg on the specially prepared surface of a garnet single crystal. Diffusion anneals at 1 atmosphere (101325 Pa) were carried out at a controlled f _{O 2} of ∼10^−17.5 bars maintained by a flowing gas mix of CO-CO₂. Annealing conditions were carefully chosen to avoid decomposition of garnet by redox reactions. High pressure anneals were carried out in a multianvil apparatus. Induced diffusion profiles (0.1–0.6 μm) were measured by an ion-microprobe with SIMS attachment. Diffusion coefficients at 1 atmosphere are in excellent agreement with extrapolation of data from high P-T experiments (Loomis et al. 1985; Chakraborty and Ganguly 1992) and also with the low temperature (750–900° C) dataset of Cygan and Lasaga (1985) if the diffusion coefficients are assumed to be proportional to f _{O 2} ^1/6. Such an f _{O 2} dependence, however, makes this dataset inconsistent with the recent dataset of Schwandt et al. (1995) on garnets of composition (Alm₁₅Pyr₇₂Gr₁₃Sp₀) unless a strong compositional dependence of Mg tracer diffusivity for Mg-rich garnets is invoked. The present experimental results show that such a compositional dependence is weak to non-existent for garnets with >38 mole percent almandine component. It is emphasized that the temperature dependence of diffusion coefficients at constant oxygen fugacities (activation energy ≈54 kcal/mol) are different from that along an oxygen fugacity buffer (activation energy ≈64.5 kcal/mol), as already pointed out by Chakraborty and Ganguly (1991). This distinction is of importance for modelling natural processes. The measurements at low temperatures either eliminate the need for, or greatly reduce the uncertainty of, extrapolation of laboratory data for modelling metamorphic processes. The high pressure results combined with those from Chakraborty and Ganguly (1992) and Loomis et al. (1985) indicate that pressure dependence of Mg tracer diffusivity in garnets is much stronger than that in forsterite (Chakraborty et al. 1994). This difference in pressure dependence of diffusivity may be caused by the difference in compressibility of the coordination polyhedra of Mg between olivines and garnets. Activation volumes of Mg tracer diffusion as high as 8 cm³/mol may be estimated using the present data in combination with earlier results. These data suggest that at a temperature of 1300° C, Mg tracer diffusion rates in garnets will decrease by an order of magnitude for every 100 km depth. The pressure effect will be stronger at lower temperatures. For calculations involving diffusion coefficients of garnets at high pressures (e.g. mantle xenoliths, eclogites) the pressure dependence of diffusivity must be taken into account. Received: 21 December 1994 / Accepted: 22 September 1995     

Significance of transition between Talchir Formation and Karharbari Formation in Lower Gondwana basin evolution — A study in West Bokaro Coal basin, Jharkhand, India

Basal part of the Gondwana Supergroup represented by Talchir and Karharbari Formations (Permo-Carboniferous) records an abrupt change-over from glacio-marine to terrestrial fluviolacustrine depositional environment. The contact between the two is an unconformity. Facies analysis of the glacio-marine Talchir Formation reveals that basal glaciogenic and reworked glaciogenic sediments are buried under storm influenced inner and outer shelf sediments. Facies associations of the Karharbari Formation suggest deposition as fluvio-lacustrine deposits in fault-controlled troughs. An attempt has been made in this paper to explain the sedimentation pattern in Talchir and Karharbari basins, and the abrupt change-over from glacio-marine to terrestrial fluviolacustrine depositional environment in terms of glacio-isostacy.     

Impact of single-point GPS integrated water vapor estimates on short-range WRF model forecasts over southern India

Specifying physically consistent and accurate initial conditions is one of the major challenges of numerical weather prediction (NWP) models. In this study, ground-based global positioning system (GPS) integrated water vapor (IWV) measurements available from the International Global Navigation Satellite Systems (GNSS) Service (IGS) station in Bangalore, India, are used to assess the impact of GPS data on NWP model forecasts over southern India. Two experiments are performed with and without assimilation of GPS-retrieved IWV observations during the Indian winter monsoon period (November–December, 2012) using a four-dimensional variational (4D-Var) data assimilation method. Assimilation of GPS data improved the model IWV analysis as well as the subsequent forecasts. There is a positive impact of ～10 % over Bangalore and nearby regions. The Weather Research and Forecasting (WRF) model-predicted 24-h surface temperature forecasts have also improved when compared with observations. Small but significant improvements were found in the rainfall forecasts compared to control experiments.     

A study on soil physico-chemical, microbial and metal content in Sukinda chromite mine of Odisha, India

Soil samples from chromite mining site and its adjacent overburden dumps and fallow land of Sukinda, Odisha, were analysed for their physico-chemical, microbial and metal contents. Chromite mine soils were heterogenous mixture of clay, mud, minerals and rocks. The pH of the soils ranges between 5.87 and 7.36. The nutrient contents of the mine soils (N, P, K and organic C) were found to be extremely low. Analysis of chromite mine soils revealed accumulation of a number of metals in high concentrations (Fe > Cr > Mn > Ni > Zn > Pb > Sr) which exceeded ecotoxicological limits in soil. Correlation and cluster analysis of metals revealed a strong relation between Cr, Ni, Fe, Mn among the different attributes studied. Assessment of different microbial groups such as fungi, actinomycetes and bacteria (heterotrophic, spore forming, free-living nitrogen fixing, phosphate solubilising and cellulose degrading) from mine soils were found to be either extremely low or absent in some soil samples. Further chromium tolerant bacteria (CTB) were isolated using 100 mg/L Cr(VI) enriched nutrient agar medium and were screened for their tolerance towards increasing concentrations of hexavalent chromium and other toxic metals. Out of 23 CTB isolates, three bacteria tolerated up to 900 mg/L, 6 up to 500 mg/L, 20 up to 200 mg/L of Cr(VI). These bacteria were also found to be sensitive towards Cu > Co > Cd and very few CTB strains could show multiple metal tolerance. These strains have great scope for their application in bioremediation of toxic chromium ions in presence of other metals ions, which needs to be explored for their biotechnological applications.     

Observation based analysis of the growth of MJO time scale from its nonlinear scale interactions with the synoptic scales

Summary The present paper addressed the issue of growth of planetary boundary-layer fluxes on the time scale of MJO based on ECMWF reanalysis daily data of 180 days covering April–September, 2001. Diagnostic analysis of this data set utilises computations of moisture and sensible heat fluxes in the frequency domain which involve nonlinear interactions phenomena of MJO time scale with the synoptic scales. Basically the whole computations performed are based on surface similarity theory and Richardson number dependent K-theory in the surface and planetary boundary layer (PBL), respectively, both invoke triple product nonlinearilies. Present observational study shows that among the totality of the triads participating in phase-locking phenomena, a prominent band of those reside in the MJO time scales (30 to 60 days) and the synoptic time scales (3 to 7 days). The study suggests that the low frequency variability on MJO time scale in moisture and sensible heat flux arises from its nonlinear interactions with synoptic time scales. The results show that the phases of the three interacting oscillations associated with specific humidity/SST, Richardson number dependent instability factor and wind shear are positive and reasonably close to each other. The amplitudes of the synoptic scale oscillations are not insignificant compared to that of MJO. These dynamical aspects regarding the phases and amplitudes of the three participating oscillations favour the nonlinear interactions of MJO to the synoptic scales and thus lead to rapid exchange of energy transfer to the former.Visiting scientist from Indian Institute of Tropical Meteorology, Pune-411008, India.