The changes in La Niña induced summertime interannual variability of sea level anomaly along the western boundary of the Bay of Bengal

Ocean Dynamics - In this study, interannual variability and associated dynamics of sea level anomaly (SLA) along the western boundary of the Bay of Bengal (WBoB) during the summer...     

Do wavelets really detect non-Gaussianity in the 4-year COBE data?

We investigate the detection of non-Gaussianity in the 4-year COBE data reported by Pando, Valls-Gabaud & Fang, using a technique based on the discrete wavelet transform. Their analysis was performed on the two DMR faces centred on the North and South Galactic poles, respectively, using the Daubechies 4 wavelet basis. We show that these results depend critically on the orientation of the data, and so should be treated with caution. For two distinct orientations of the data, we calculate estimates of the skewness, kurtosis and scale–scale correlation of the corresponding wavelet coefficients in all of the available scale domains of the transform. We obtain several detections of non-Gaussianity in the DMR-DSMB map at greater than the 99 per cent confidence level, but most of these occur on pixel–pixel scales and are therefore not cosmological in origin. Indeed, after removing all multipoles beyond ℓ=40 from the COBE maps, only one robust detection remains. Moreover, using Monte Carlo simulations, we find that the probability of obtaining such a detection by chance is 0.59. We repeat the analysis for the 53+90 GHz coadded COBE map. In this case, after removing ℓ>40 multipoles, two non-Gaussian detections at the 99 per cent level remain. Nevertheless, again using Monte Carlo simulations, we find that the probability of obtaining two such detections by chance is 0.28. Thus, we conclude the wavelet technique does not yield strong evidence for non-Gaussianity of cosmological origin in the 4-year COBE data.     

The disturbances in an infinite inhomogeneous medium due to transient forces and twists on the surface of a buried spherical source

Summary In this paper the disturbances in an inhomogeneous medium due to two types of forces (i) transient normal forces, (ii) transient twists in presence of a buried spherical source has been considered. The material of the inhomogeneous medium is assumed to be transversely isotropic. The results are in terms of modified Bessel functions. In a particular case, the equation reduces to an ordinary differential equation of second order.     

Monitoring the impact of coal mining and thermal power industry on landuse pattern in and around Singrauli Coalfield using Remote Sensing data and GIS

Singrauli Coalfield spreading over an area of about 300 sq km along Uttar Pradesh and Madhya Pradesh border in the central part of India, is witnessing rapid industrialisation due to a large number of open pit coal mining projects and Super Thermal Power Station (STPS). Large scale mining activities along with operation of STPS have generated a great deal of environmental stress not only on the landuse pattern but also on various ecosystems in this region. An integrated remote sensing study was conducted to assess the impact of industrialisation on landuse pattern in the area under reference. The multispectral, multi-temporal data (1975, 1986 & 1991) of LANDSAT MSS and TM duly supplemented with ground truth were studied for generation of multidate landuse maps. Data base for landuse for the years 1975, 1986 and 1991 was created using PAMAP GIS for landuse analysis and change detection for optimal utilisation, planning and management of land resources. The study has revealed that the areas under built-up land, mining and fly ash pond have increased substantially from 1975 to 1991. Loss in forest cover and agricultural land has occurred due to rapid industrialisation in this region. It has been observed from the comparison of 1986 and 1991 data that the wasteland generated due to deforestation for initiating coal mining projects has gradually been reclaimed under operation “Green Gold” launched by Northern Coalfields Ltd. Further the wastelands have been effectively utilised for establishing the STPS, townships as well as other infrastructures in this area.     

The interaction of an obliquely incident plane electromagnetic wave with an anisotropic moving conducting half-space

The interaction of an obliquely incident plane electromagnetic wave with an anisotropic moving conducting medium described by tensor constitutive parameters is studied. Starting from the Maxwell-Minkowski equations the wave solutions in the laboratory frame, the modified law of refraction and the reflecton and the transmission coefficients are obtained both for incidentE- andH-waves, corresponding to the two specific orientations of the plane of incidence relative to the direction of motion of the medium. The reflection and the transmission coefficients for a moving conducting medium do not, in general, add to unity resulting in the possibility of energy transference between the moving medium and the transmitted wave. Further the various reflection and transmission characteristics are modified in an interesting manner due to the finite conductivity, the anisotropy and the motion of the medium. Numerical results for the reflection and the transmission coefficients are presented for a range of the parameters characterizing the anisotropy and the velocity of the moving medium.     

Solar-wind interactions: Nature and composition of lunar atmosphere

The solar wind interacts directly with the lunar surface material resulting in an essentially complete absorption of the corpuscles producing no upstream bowshock but a cavity downstream from the Moon. The main source of most neutral species of the atmosphere, except probably⁴⁰Ar, is the solar-wind interaction products. The other sources which appear to be minor contributors to the atmosphere are the interaction products of cosmic rays, planetary degassing, effects of meteorite impacts and radioactive decays. Most of the hydrogen atoms derived from the solar-wind protons contribute to the atmosphere as hydrogen molecules rather than atoms. Only on the basis of the solar-wind protons, alpha particles and ions of oxygen and carbon, the atmospheric species concentration (cm^–3) near the lunar surface at 300K are as follows: H₂ 3.3 to 9.9 × 10³; He 2.4 to 4.7 × 10³; H 3.7; OH 0.25; H₂O 0.24; and O₂, O, CO, CO₂ and CH₄ in concentrations smaller than H₂. Whatever the source, the OH and H₂O concentrations in the atmosphere are about the same. The calculated concentrations are in good agreement with the observations by the Apollo 17 lunar surface mass spectrometer and the Apollo 17 orbital UV spectrometer. At the time of sample collection from the Moon, the hydrogen content in the trapped gas layer of the lunar surface material was partly as hydrogen atoms and partly as hydrogen molecules, but at the time of sample analysis hydrogen was mostly in molecular form. The H₂O content at the time of sample analysis was only a few parts per million by weight.Paper presented at the Conference on Interactions of the Interplanetary Plasma with the Modern and Ancient Moon, sponsored by the Lunar Science Institute, Houston, Texas and held at the Lake Geneva Campus of George Williams College, Wisconsin, between September 30 and October 4, 1974.