Observations of trace gases and aerosols over the Indian Ocean during the monsoon transition period

Characteristics of trace gases (O3, CO, CO2, CH4 and N2O) and aerosols (particle size of 2.5 micron) were studied over the Arabian Sea, equatorial Indian Ocean and southwest part of the Bay of Bengal during the monsoon transition period (October-November, 2004). Flow of pollutants is expected from south and southeast Asia during the monsoonal transition period due to the patterns of wind flow which are different from the monsoon period. This is the first detailed report on aerosols and trace gases during the sampled period as the earlier Bay of Bengal Experiment (BOBMEX), Arabian Sea Monsoon Experiment (ARMEX) and Indian Ocean Experiments (INDOEX) were during monsoon seasons. The significant observations during the transition period include: (i) low ozone concentration of the order of 5 ppbv around the equator, (ii) high concentrations of CO2, CH4 and N2O and (iii) variations in PM2.5 of 5-20μg/m3

Optimal nonlinear wind analysis over the Indian region by iterative correction scheme

The development of satellite observing systems (asynoptic observations) has led to the idea that dynamical evolution of atmospheric flow should be explicitly taken into account while defining the initial conditions of the forecast. In view of this, objective analysis of wind field over the Indian region has been made by applying an iterative analysis correction scheme proposed by Lorenc Lorenc A C, Q J R Meteorol Soc (UK), 112 (1986) 1177. The most likely analysis of wind field for a given set of observations is obtained. In this process, at each iteration, the height values are estimated from wind field by nonlinear balance equation. Their partial derivatives with reference to wind field are used in modifying the weights and to obtain the convergence. The solution of the iteration is the most likely analysis of wind field. The scheme has been tested for two cases of monsoon depressions, 2-5 August 1988 and 28-30 July 1991. The analysis has been compared with the conventional linear optimum interpolation analysis. Divergence and vorticity computed from both the analysed wind fields have been examined. Synoptic features depicted in both the analyses are similar and agree with cloud pictures, suggesting that the scheme has performed well and also it is possible to introduce the information on approximate geostrophic balance in assimilation process

Optimal nonlinear wind analysis over the Indian region by iterative correction scheme

156-167The development of satellite observing systems (asynoptic observations) has led to the idea that dynamical evolution of atmospheric flow should be explicitly taken into account while defining the initial conditions of the forecast. In view of this, objective analysis of wind field over the Indian region has been made by applying an iterative analysis correction scheme proposed by Lorenc [Lorenc A C, Q J R Meteorol Soc (UK) 112 (1986) 1177]. The most likely analysis of wind field for a given set of observations is obtained. In this process, at each iteration, the height values are estimated from wind field by nonlinear balance equation. Their partial derivatives with reference to wind field are used in modifying the weights and to obtain the convergence. The solution of the iteration is the most likely analysis of wind field. The scheme has been tested for two cases of monsoon depressions, 2-5 August 1988 and 28-30 July 1991. The analysis has been compared with the conventional liner optimum interpolation analysis. Divergence and vorticity computed from both the analysed wind fields have been examined. Synoptic features depicted in both the analyses are similar and agree with cloud pictures, suggesting that the scheme has performed well and also it is possible to introduce the information on approximate geostrophic balance in assimilation process

Etude des conséquences de l'évolution de la structure chimique sur la variation des propriétés physiques de polymères soumis à un vieillissement photochimique

L'exposition des polymères aux contraintes de leur environnement d'usage provoque une modification de la structure chimique des macromolécules qui se traduit par une évolution irréversible de leurs propriétés fonctionnelles. L'objectif majeur de cette thèse était de passer, dans la compréhension des phénomènes de photovieillissement, du niveau moléculaire au niveau macroscopique. Pour ce faire, trois polymères dont le vieillissement est gouverné par des réactions de re ticulation et / ou de coupures de chaîne, ont été étudiés. Nous avons principalement développé l'utilisation de la microscopie à force atomique en effectuant des nanoindentations tant à la surface que dans l'épaisseur du matériau irradié et comparé les résultats à de nombreuses autres techniques. Cette méthodologie nous a permis de progresser dans la connaissance des relations qui existent entre modification de la structure chimique et variation des propriétés physiques de polymères sous l'impact du photovieillissementCLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

Comparative sorption of chromium species as influenced by pH, surface charge and organic matter content in contaminated soils

Excessive use of chromium (Cr) in several industrial applications has a significant impact on soil biota. Chromium when present in soil and water occurs in two forms [Cr(III) and Cr(VI)] which exhibit contrasting characteristics and therefore retention of these two species is of prime importance to arrest Cr contamination in the environment. In this study, the effect of lime, elemental sulfur (to change pH), Fe(III) oxide (for surface charge) and cow manure (organic matter content) was tested on the retention capacity of Cr(III) and Cr(VI) in contaminated soils. The results showed that the addition of lime increased Cr(III) retention while elemental sulfur (So), Fe(III) oxide and cow manure increased Cr(VI) retention. The effect of So on Cr(VI) sorption is mediated through a decrease in soil pH, which facilitated an increased retention of Cr(VI) as measured by Freundlich sorption coefficient from 0.079 (in pristine soil, pH 7.15) to 21.06 L/kg (in So amended soil, pH 4.08). Also, Fe(III) oxide addition at 5% has favoured for an increase in the retention of Cr(VI) (Kf = 91.15 L/kg). Cow manure promoted Cr(VI) reduction, possibly due to the presence of functional groups that are present along with dissolved organic carbon and also by increased microbial activity. It is concluded that the mitigation of Cr toxicity is brought about by the addition of amendments which manipulate the properties of soil to increase retention of Cr(III) and Cr(VI)