Geographic Information System and groundwater quality mapping in Panvel Basin,Maharashtra, India

Panvel Basin of Raigarh district, Maharashtra, India is the study area for groundwater quality mapping using the Geographic Information System (GIS). The study area is typically covered by Deccan basaltic rock types of Cretaceous to Eocene age. Though the basin receives heavy rainfall, it frequently faces water scarcity problems as well as water quality problems in some specific areas. Hence, a GIS based groundwater quality mapping has been carried out in the region with the help of data generated from chemical analysis of water samples collected from the basin. Groundwater samples show quality exceedence in terms of chloride, hardness, TDS and salinity. These parameters indicate the level of quality of groundwater for drinking and irrigation purposes. Idrisi 32 GIS software was used for generation of various thematic maps and for spatial analysis and integration to produce the final groundwater quality map. The groundwater quality map shows fragments pictorially representing groundwater zones that are desirable and undesirable for drinking and irrigation purposes.     

Differential Alteration of Ilmenite in a Tropical Beach Placer, Southern India: Microscopic and Electron Probe Evidences

Abstract. The study based on microscopic and microprobe techniques reveals that ilmenite of Manavalakurichi deposit has generally reached the alteration phase of 'leached ilmenite'. The XRD and bulk chemical analysis confirm the limited alteration undergone by ilmenite grains. Ilmenite alteration has been found to be a process of continuous leaching of iron from the mineral lattice and hydroxylisation. The enrichment of trace elements with progressive alteration is discussed. Si and Al are enriched by more than 100 fold. The prevalence of reducing environment at present in the deposit indicates that the oxidation of ferrous iron leading to pseudorutile formation would have occurred during transportation of sediments.     

Observations of the atmospheric surface layer parameters over a semi arid region during the solar eclipse of August 11th, 1999

This paper discusses the observations of the Atmospheric Surface Layer (ASL) parameters during the solar eclipse of August 11th, 1999. Intensive surface layer experiments were conducted at Ahmedabad (23‡21′N, 72‡36′E), the western part of India, which was close to the totality path. This rare event provided by nature is utilised to document the surface layer effects during the eclipse period using measurements of high frequency fluctuations of temperature, tri-axial wind components as well as mean parameters such as temperature, humidity, wind speed and subsoil temperature. Analysis showed that during the eclipse period, the turbulence parameters were affected leading to the suppression of the turbulence process, the main dynamic process in the atmospheric boundary layer, while the mean parameters showed variations within the natural variability of the observational period. The spectra of the wind components and temperature indicated decrease in spectral power by one order in magnitude during the eclipse period. The rate of dissipation of turbulent kinetic energy is found to decrease by more than one order during the eclipse period. The stability parameter showed a change from unstable to stable condition during the period of eclipse and back to unstable condition by the end of eclipse     

Fluxes of material in the Arabian Sea and Bay of Bengal — Sediment trap studies

In order to investigate how monsoons influence biogeochemical fluxes in the ocean, twelve time-series sediment traps were deployed at six locations in the northern Indian Ocean. In this paper we present particle flux data collected during May 1986 to November 1991 and November 1987 to November 1992 in the Arabian Sea and Bay of Bengal respectively. Particle fluxes were high during both the SW and NE monsoons in the Arabian Sea as well as in the Bay of Bengal. The mechanisms of particle production and transport, however, differ in both the regions. In the Arabian Sea, average annual fluxes are over 50gm^-2y^-1 in the western Arabian Sea and less than 27gm^-2 y^-1 in the central part. Biogenic matter is dominant at sites located near upwelling centers, and is less degraded during peak flux periods. High particle fluxes in the offshore areas of the Arabian Sea are caused by injection of nutrients into the euphotic zone due to wind-induced mixed layer deepening. In the Bay of Bengal, average annual fluxes are highest in the central Bay of Bengal (over 50gm^-2y^-1) and are least in the southern part of the Bay (37gm^-2y^-1). Particle flux patterns coincide with freshwater discharge patterns of the Ganges-Brahmaputra river system. Opal/carbonate and organic carbon/carbonate carbon ratios increase during the SW monsoon due to variations in salinity and productivity patterns in the surface waters as a result of increased freshwater and nutrient input from rivers. Comparison of S years data show that fluxes of biogenic and lithogenic particulate matter are higher in the Bay of Bengal even though the Arabian Sea is considered to be more productive. Our results indicate that in the northern Indian Ocean interannual variability in organic carbon flux is directly related to the strength and intensity of the SW monsoon while its transfer from the upper layers to the deep sea is partly controlled by input of lithogenic matter from adjacent continents.     

Monsoon activity and coupling between low-latitude and high-latitude stratospheric activities

From a Fourier analysis of the monthly mean values of the northern hemispheric geopotential heights at 30 and 50 mb levels, for the period 1972–1979, the transports of momentum and of sensible heat, and the energy conversion terms,C(K _E ,K _Z ) andC(A _Z ,A _E ), have been computed along 30°N and 60°N latitutudes. The variation in these dynamical parameters at 60°N, in relation to monsoon activity in low latitudes and the easterly and westerly phases of the QBO over Gan Island, suggest that a coupling may exist between the high-latitude stratospheric changes and low-latitude monsoon activity and that the low-latitude stratospheric activity modulates high-latitude circulation, confirming the results obtained byHolton andTan (1980) and byLabitzke (1983). The study of the low-latitude stratospheric changes in relation to the high-latitude warmings also indicates a linkage between the low- and high-latitude features     

Estimation of source function and medium response function by autoregressive method

By modelling seismograms as “low” and “high” order autoregressive (AR) processes, the source function and the medium response function are separated from a single channel seismogram. Akaike's final prediction error is used as a statistic to select the appropriate “low” and “high” AR order of the process. Case studies of synthetic data show that the recovered source and reflectivity functions compare very well with the input functions. Using this method, arrivals of the surface reflected P phases of five explosions from the Soviet region and of two earthquakes from Kamchatka, recorded at Gauribidanur Seismic Array (GBA), India, are identified. Certain features of the source and source region of these events are also inferred.     

Dynamics of the stationary eddies in the lower stratospheric circulation in the wavenumber domain and monsoon activity

Meridional transports of momentum and sensible heat have been computed using the Fourier coefficients of the geopotential heights at 50 mb and 30 mb levels for each month during the years 1972 to 1979. Seasonal variations in these transports and in the energy conversionsC (K _E ,K _Z ) andC (A _z ,A _E ) in the contrasting years of monsoon activity have been discussed. The transport and the conversion terms undergo annual variations only with winter maxima and summer minima. Large northward transport of momentum and of sensible heat in the low latitude summer and in the high latitude preceeding winter suggests a linkage between monsoon activity and high latitude stratosphere. Seasonal variations in the energy conversion termsC (K _E ,K _Z ) andC (A _Z ,A _E ) conform with the changes in the system in the years of widely differing monsoon activity both in low and high latitudes. Large conversion of energy fromA _Z toA _E in low latitude summer indicates weakening of the existing meridional temperature gradient, in bad monsoon years.     

A comparative study of implicit and explicit initialization for a tropical barotropic model

The explicit nonlinear normal mode initialization (ENMI) scheme is applied to a tropical barotropic limited area shallow water model in spherical coordinates. The model is formulated by considering potential enstrophy conserving finite difference scheme. It is seen from the results of this study that the ENMI scheme is fully capable of filtering out the spurious gravity wave oscillations. The results are compared with those using an implicit nonlinear normal mode initialization (INMI). The latter scheme gives equally satisfactory results, requiring less computational time than the explicit scheme.     

Impact of aerosols from the Asian Continent on the adjoining oceanic environments

Aerosol optical depth (AOD) at 630 nm wavelength over the oceanic regions adjoining the Asian Continent is examined using a seven-year long data base derived from the Advanced Very High Resolution Radiometer (AVHRR) on board NOAA satellite to study the mean spatial and temporal variations as well as to understand the impact of aerosols advecting from the continent. Depending on the prevailing meteorological conditions and nature of synoptic circulation, the AOD over the oceanic region shows a systematic annual variation. This annual pattern inturn also shows an inter-annual variability because of the corresponding variations in the meteorological features over the continent as well as small-scale deviations in the nature of synoptic circulation. The annual variation over the oceanic regions also shows a pronounced spatial heterogeneity depending on the influence of continental aerosols. Making use of the wind speed dependence of sea-salt AOD at far-oceanic environments and monthly mean wind speeds at small grids of size 5° × 5°, the annual variation of sea-salt AOD at different locations is studied to understand the spatial heterogeneity of this component. The residual component obtained by subtracting this from the measured AOD is the non-oceanic component due to advection from continent. The source regions for major continental advections are delineated from the analysis of air-mass back trajectories at appropriate locations identified from the annual pattern of non-oceanic component. The long-term effect of the continental impact is examined from the mean trend of AOD over the three major oceanic regions. This study shows that the continental influence is most significant over the Arabian Sea, followed by the Bay of Bengal and is almost insignificant in most of the regions over the Southern Hemispheric Indian Ocean, except for the effect of smoke aerosols over a few locations near Indonesia and Madagascar.     

Repeated load tests on geosynthetic reinforced unpaved road sections

This paper presents the experimental results from laboratory repeated plate load tests on unreinforced and reinforced model sections of unpaved road constructed in a steel test tank. Different types of geosynthetics, namely, geotextile, two types of biaxial geogrids and geocells were used to reinforce the road sections in different tests. The effect of type and form of reinforcement on the stress-strain hysteresis of unpaved road sections is discussed in the light of experimental results. Model tests were also conducted with varying heights and positions of geocell layer to study the effect of these parameters on deformations and surface profiles. It was observed that at higher settlements, the reinforced systems developed less permanent settlements and more elastic settlements compared to unreinforced systems. Increasing the height of the geocell layer resulted in improved performance up to a certain height, beyond which, further increase in the height reduced the load resistance because of the inadequate granular overlay thickness.