Guided wave propagation in a moving magnetized plasma bounded by parallel perfectly conducting planes

The structure of the Saturnian rings is compared with the asteroidal belt and the relative importance of the resonance effects and the cosmogonic effects is evaluated. No visible correspondence to the Kirkwood gaps is expected theoretically, nor is there any observational evidence for such effects. The only possible resonance is the 1:1 resonance with Saturn's spin period.Cosmogonic shadow effects are responsible for the main features of the ring structure, including Cassini's division, the limit between the B and C ring, and possibly also Guérin's division.     

The Air-Coastal Sea Chemical Exchange: A Case Study on the New Jersey Coast

The coastal marine atmosphere adjacent to large urban and industrial centers is in general strongly impacted by pollution emissions, resulting in high loading of pollutants in the ambient air. Among the airborne substances are certain trace elements from a variety of emission sources that can serve as micronutrients to marine organisms in coastal waters. High concentrations of such elements in coastal air can result in enhanced air-to-sea deposition fluxes to coastal waters. They could also be transported over the open ocean, affecting the composition of the remote marine atmosphere and then ocean ecosystems. To provide better understanding of the extent of air-to-sea deposition processes on the New Jersey coast, a heavily polluted coastal region on the US East Coast, a synthesis of observation data was carried out for selected trace elements, including Fe, Cd, Cr and Cu, derived from measurements of both size-segregated and bulk aerosol particles, as well as precipitation around the New Jersey coast. The atmospheric input of Hg was also estimated based on measurement data. Results indicated that the total deposition fluxes of most trace elements were higher in Northern coastal NJ compared to Southern coastal NJ, reflecting the differences in the source strengths of these element emissions between the two coastal regions. Dry deposition processes were more significant for common dust-derived elements, particularly Fe and Al, compared with their wet deposition fluxes. However, the processes of precipitation scavenging appeared to be more important for the elements that were often enriched in fine particles including Zn, Cu, Pb and Ni. The removal of Hg from the ambient air was overwhelmingly dominated by atmospheric wet deposition. In the future, atmospheric measurements at more sites on the NJ coast should be performed simultaneously to reduce the spatial and temporal uncertainties associated with atmospheric deposition fluxes estimated in this study.     

Perturbations in tropical middle atmosphere during winter, 1984–1985

Summary Using high altitude rocketsonde data for Thumba (8.5 N, 76.9E) and Balasore (21.5 N, 86.9E) and the stratalert messages for high latitudes for the winter (December–March) 1984–1985, an examination has been made to study the perturbations in the temperature and winds in the tropical middle atmosphere and their linkage with the dynamical events occurring over the high-latitude middle atmosphere during that winter.The results of analysis indicated occurrence of strong cooling in the mesosphere over a period of seven days (5–12 December 1984) and the depth of the cooling layer was 15 km. This incident was followed by a strong warming over a period of seven days (12–19 December 1984) and the depth of the warming layer was 13 km. The major warming event, which occurred over high latitudes during the later part of December and the first week of January, was followed by the cooling in the mesosphere and warming in the stratosphere at Thumba. Also the zonal winds were strong easterly and the meridional winds were northerly in the upper stratosphere and the lower mesosphere over tropics during the same period. Weaker zonal winds/stronger easterly winds were generally noticed to be associated with coolings/warmings over tropics.With 7 Figures     

Contamination of shallow aquifers by arsenic in upper reaches of Tista river at Siliguri–Jalpaiguri area of West Bengal, India

Arsenic is present in groundwater at Siliguri–Jalpaiguri area, West Bengal, India. This is the place where Tista river descending from the Himalayas meets the alluvial plain. The area represents alluvial fan and floodplains of Tista, Mahananda-Balasan, Jaladhaka and its tributaries. In the river sediment samples, para- and ferro-magnetic minerals within 0.3–0.05 mm fraction contain 9–80 ppm of arsenic. The study indicates that iron bearing minerals viz. biotite, hornblende as well as iron coated grains of the sediment are major contributors towards arsenic budget. Though magnetite as a mineral shows maximum arsenic content (22 ppm), it is volumetrically not of much significance. Measurement of groundwater collected from tube wells shows up to 0.05 ppm of arsenic. These arsenic contaminated tube wells occur in a linear fashion along the course of the rivers. Moreover, localization of contaminated tube wells coincides with the change of channel gradient as observed in longitudinal section. The study enumerates a cause–effect relationship of arsenic occurrence with river gradient and fluvial sedimentation.     

Study of subsurface geology in locating arsenic-free groundwater in Bengal delta,West Bengal,India

Over a large area of the Bengal delta in West Bengal, India, arsenic distribution patterns in groundwater were studied. One hundred and ten boreholes at different target locations were made, subsurface sediments were logged and analysed, and arsenic values in sediments vis-à-vis groundwater were compared. The study elucidates the subsurface geology of the western part of Bengal delta and characterises the sediments that were intersected in different boreholes with contrasting values of arsenic in groundwater. It reveals an existence of multiple aquifers stacked over each other. Depending on the color and nature of aquifer-sands and their overlying clay beds six aquifer types (Type-1 to Type-6) are classified and described. Sediment-arsenic for all the varieties of aquifer sands are near similar but the groundwater-arsenic of these six aquifers varies widely. Type-2 and Type-5 aquifers host arsenic-contaminated groundwater whereas the other four aquifers are arsenic-free. Type-2 and Type-5 aquifers are capped by a grey to dark grey soft organic matter-rich clay unit which makes these aquifers semi-confined to leaky-confined. These contribute in releasing arsenic from the sediments. The results of this study are employed in a proposed georemedial measure against this hazardous toxic element.     

Investigation of dominant modes of monsoon ISO in the northwest and eastern Himalayan region

This study investigates the altitudinal variation of dominant modes of summer monsoon intra-seasonal oscillation (ISO) over the Northwest (NWH) and Eastern Himalayan (EH) region using (i) spatially scattered 133 number of station rainfall observations and (ii) latitudinal transect-wise (LT) rainfall variation, obtained from an observed interpolated gridded rainfall data for the period 1995–2004. The altitudinal variation of dominant modes of monsoon ISO were investigated by exploring the strong and weak phases of the principal components of 10–90 days bandpass rainfall data of June to September with respect to location specific station height. Investigation of frequency of days for light and moderate rainfall along with the occurrence of total seasonal rainy days has revealed existence of a rainfall maximum around 2100 m height for the NWH region. Similarly, the total seasonal rainy days of EH region was found to have maxima between 1100 and 1400 m height. Analyses of the spatially scattered station rainfall observation for the NWH region showed that the strong periods of ISO modes exist around 747.9 (±131.7) m and 2227.2 (±100.2) m heights. Over the EH region, the dominant modes of the monsoon ISO were found to be centred around 1200 m. Significant alterations of strong and weak phases of monsoon ISO as a response to altitudinal variation in the mountain surface were observed when latitudinal transect-wise variation of monsoon ISO modes were investigated.     

Nature and origin of arsenic carriers in shallow aquifer sediments of Bengal Delta,India

Sediments from shallow aquifers in Bengal Delta, India have been found to contain arsenic. Rivers of Ganga-Brahmaputra system, responsible for depositing these sediments in the delta, have created a store of arsenic. Geomorphological domains with different depositional styles regulate the pattern of distribution of zones with widely different content of groundwater arsenic. The high arsenic zones occur as narrow sinuous strips confined to channel deposits. A few iron-bearing clastic minerals and two post-depositional secondary products are arsenic carriers. Secondary siderite concretions have grown on the surface of the clastic carriers in variable intensity. The quantity of arsenic in all clastic carriers is in excess of what is generally expected. Excess arsenic is contributed by the element adsorbed on the concretion grown on the surface of the carriers, which adds up to the arsenic in the structure of the minerals. Variable abundance of concretions is responsible for the variable quantity of arsenic in the carriers and the sediment samples. Fe²⁺ for the growth of siderite concretions is obtained from the iron-bearing clastic carriers. The reaction involves reduction of trivalent iron to bivalent and the required electron is obtained by transformation of As³⁺ to As⁵⁺. It is suggested that oxidation of As³⁺ to As⁵⁺ is microbially mediated. In the Safe zone arsenic is retained in the carriers and groundwater arsenic is maintained below 0.05 mg/l. In the Unsafe zone sorbed arsenic is released from the carriers in the water through desorption and dissolution of concretion, thereby elevating the groundwater arsenic level to above 0.05 mg/l.