Dust ion acoustic (DIA) solitary waves in plasmas with weak relativistic effects in electrons and ions

In the new investigation of dust-ion acoustic (DIA) waves with negative dust charges and weakly relativistic ions and electrons in the plasma, compressive and rarefactive DIA solitons of interesting characters are established through the Korteweg-de Vries (KdV) equation. Eventually, the amplitudes of the compressive DIA solitons are found to be constant at some critical temperature ratio α _c (electron to ion temperature ratio) identifying some critical dust charge Z _dc . It is predicted, that the reception of dust charges by the plasma particles at the variation of temperature starts functioning to the growth of compressive soliton’s constant stage of amplitude after the state of critical α _c . The identification of critical dust charge (Z _dc ) which is found to be very great for solitons of constant amplitudes becomes feasible for very small dust to ion density ratio (σ). But it can be achieved, we observe, due to the relativistic increase in ion-density as in mass, which is also a salient feature of this investigation.     

Chemical weathering in the Krishna Basin and Western Ghats of the Deccan Traps, India: Rates of basalt weathering and their controls

Rates of chemical and silicate weathering of the Deccan Trap basalts, India, have been determined through major ion measurements in the headwaters of the Krishna and the Bhima rivers, their tributaries, and the west flowing streams of the Western Ghats, all of which flow almost entirely through the Deccan basalts.Samples (n = 63) for this study were collected from 23 rivers during two consecutive monsoon seasons of 2001 and 2002. The Total dissolved solid (TDS) in the samples range from 27 to 640 mg l⁻¹. The rivers draining the Western Ghats that flow through patches of cation deficient lateritic soils have lower TDS (average: 74 mg l⁻¹), whereas the Bhima (except at origin) and its tributaries that seem to receive Na, Cl, and SO₄ from saline soils and anthropogenic inputs have values in excess of 170 mg l⁻¹. Many of the rivers sampled are supersaturated with respect to calcite. The chemical weathering rates (CWR) of “selected” basins, which exclude rivers supersaturated in calcite and which have high Cl and SO₄, are in range of ∼3 to ∼60 t km⁻² y⁻¹. This yields an area-weighted average CWR of ∼16 t km⁻² y⁻¹ for the Deccan Traps. This is a factor of ∼2 lower than that reported for the Narmada-Tapti-Wainganga (NTW) systems draining the more northern regions of the Deccan. The difference can be because of (i) natural variations in CWR among the different basins of the Deccan, (ii) “selection” of river basin for CWR calculation in this study, and (iii) possible contribution of major ions from sources, in addition to basalts, to rivers of the northern Deccan Traps.Silicate weathering rates (SWR) in the selected basins calculated using dissolved Mg as an index varies between ∼3 to ∼60 t km⁻² y⁻¹, nearly identical to their CWR. The Ca/Mg and Na/Mg in these rivers, after correcting for rain input, are quite similar to those in average basalts of the region, suggesting near congruent release of Ca, Mg, and Na from basalts to rivers. Comparison of calculated and measured silicate-Ca in these rivers indicates that at most ∼30% of Ca can be of nonsilicate origin, a likely source being carbonates in basalts and sediments.The chemical and silicate weathering rates of the west flowing rivers of the Deccan are ∼4 times higher than the east flowing rivers. This difference is due to the correspondingly higher rainfall and runoff in the western region and thus reemphasises the dominant role of runoff in regulating weathering rates. The silicon weathering rate (SWR) in the Krishna Basin is ∼15 t km⁻² y⁻¹, within a factor of ∼2 to those in the Yamuna, Bhagirathi, and Alaknanda basins of the Himalaya, suggesting that under favourable conditions (intense physical weathering, high runoff) granites and the other silicates in the Himalaya weather at rates similar to those of Deccan basalts. The CO₂ consumption rate for the Deccan is deduced to be ∼3.6 × 10⁵ moles km⁻² y⁻¹ based on the SWR. The rate, though, is two to three times lower than reported for the NTW rivers system; it still reinforces the earlier findings that, in general, basalts weather more rapidly than other silicates and that they significantly influence the atmospheric CO₂ budget on long-term scales.     

A study on the structure of the convective atmosphere over the Bay of Bengal during BOBMEX-99

Convective activity is one of the major processes in the atmosphere influencing the local and large-scale weather in the tropics. The latent heat released by the cumulus cloud is known to drive monsoon circulation, which on the other hand supplies the moisture that maintains the cumulus clouds. An investigation is carried out on the convective structure of the atmosphere during active and suppressed periods of convection using data sets obtained from the Bay of Bengal and Monsoon Experiment (BOBMEX). The cumulus convection though being a small-scale phenomenon, still influences its embedding environment by interaction through various scales. This study shows the variation in the kinematic and convective parameters during the transition from suppressed to active periods of convection. Convergence in the lower levels and strong upward vertical velocity, significant during active convection are associated with the formation of monsoon depressions. The apparent heat source due to latent heat release and the vertical transport of the eddy heat by cumulus convection, and the apparent moisture sink due to net condensation and vertical divergence of the eddy transport of moisture, are estimated through residuals of the thermodynamic equation and examined in relation to monsoon activity during BOBMEX.     

Simultaneous measurement of humidity and temperature in the lower troposphere over Chung-Li,Taiwan

A combined Raman–Rayleigh lidar has been designed at Chung-Li, Taiwan for the simultaneous measurement of water-vapor mixing ratio, temperature and extinction-to-backscatter ratio of aerosol in the lower troposphere. The technique of Raman–Rayleigh lidar can retrieve correct temperature profile in the lower troposphere where the measurements are underestimated due to the aerosol loading. Two typical cases are discussed under different humidity (dry/wet) conditions. The water vapor and temperature profile have shown a good agreement with radiosonde. Simultaneous measurement of Raman–Rayleigh lidar also illustrates the physical nature of the aerosol and is useful in understanding the effects of humidity on aerosol swelling.     

Exsolution textures in orthopyroxene in aluminous granulites as indicators of UHT metamorphism: New evidence from the Eastern Ghats Belt, India

Highly aluminous orthopyroxene, coexisting with sapphirine, cordierite, sillimanite, quartz and garnet in various combinations, constitute granoblastic mosaic peak metamorphic assemblages in aluminous granulites from three localities in the Eastern Ghats Belt, India. Orthopyroxene contains four types of intergrowths: (a) involving sapphirine with or without cordierite, (b) involving spinel, but without sapphirine, (c) involving cordierite, but without sapphirine and spinel, and (d) involving garnet, without sapphirine, spinel or cordierite. On the basis of textural and compositional data, origin of the intergrowths is ascribed to breakdown of Mg-Tschermak component, locally also involving Fe- and Ti-Tschermak. An attempt is made to compute the “pre-breakdown” compositions of orthopyroxene by image analysis, which shows maximum Al₂O₃ content of 13.4 wt.% in the pristine orthopyroxene. Geothermometry, phase equilibria consideration and application of existing experimental data on alumina solubility in orthopyroxene coexisting with sapphirine and quartz, collectively indicate extreme thermal conditions of metamorphism (> 1000 °C) for the studied assemblages. This re-affirms the notion that Al₂O₃ solubility in orthopyroxene is the most powerful indicator of UHT metamorphism (Harley, S.L., 2004. Extending our understanding of ultrahigh temperature crustal metamorphism. J. Mineral. Petrol. Sci. 99, 140–158). The intergrowths are considered to have formed due to cooling from the thermal peak spanning a temperature range of approximately 150 °C. Appearance of diverse types of intergrowths is probably related to subtle differences in bulk composition, particularly Fe:Mg ratios.     

Experimental calibration of lake-sediment spectral reflectance to chlorophyll a concentrations: methodology and paleolimnological validation

Chlorophyll a preserved in lake sediments reflects, in part, past primary production. This study assesses the spectral properties of sedimentary chlorophyll a using visible-near infrared reflectance (VNIR) spectroscopy, with the objective of establishing a new, non-destructive paleolimnological proxy. Reflectance spectra were determined from a dilution series (n = 10) involving incremental additions of pulverized modern algae to a lake sediment matrix of low organic content. This enabled an assessment of the development of sediment reflectance spectra in relation to different sediment chlorophyll a concentrations, and subsequent regression of spectral features against measured concentrations of chlorophyll a and derivatives obtained by high performance liquid chromatography (HPLC). The experiment demonstrates that ubiquitous troughs in sediment reflectance near 675 nm are attributable to chlorophyll a and derivative compounds. A significant correlation (r ² = 0.98, P < 0.01) was obtained between the area of the reflectance trough in the 650–700 nm interval and summed concentrations of chlorophyll a, all derivative isomers, and degradational pheopigments. A simple linear inference model derived from this experiment was applied to a down-core sequence of VNIR spectra from a productive prairie lake (Alberta, Canada), where it produced inferred sediment chlorophyll a concentrations in concordance with HPLC measurements. Although a larger training set is desirable to further refine the inference model, the analyses reported here demonstrate that reflectance spectroscopy provides a rapid, semi-quantitative method for assessing the chlorophyll a content of lake sediments.