The complex gravitational lens system B1933+503

We report the discovery of the most complex arcsec-scale radio gravitational lens system yet known. B1933+503 was found during the course of the CLASS survey and MERLIN and VLA radio maps reveal up to 10 components. Four of these are compact and have flat spectra; the rest are more extended and have steep spectra. The background lensed object appears to consist of a flat-spectrum core (quadruply imaged) and two compact 'lobes' symmetrically disposed relative to the core. One of the lobes is quadruply imaged while the other is doubly imaged. An HST observation of the system with the WFPC2 shows a galaxy with an axial ratio of 0.5, but none of the images of the background object is detected. A redshift of 0.755 has been measured for the lens galaxy.     

Modelling the 10-image lensed system B1933+503

A gravitational lens model is presented for the newly discovered 10-image system B1933+503. The underlying object, revealed by modelling, is a triple radio source on the scale of a couple of hundred mas that is well-aligned along the line of sight with a foreground and somewhat flattened lensing galaxy, the orientation and location of which match those of an observed galaxy, known to be at a redshift of 0.755. Uncertainties in the modelling are obtained by a Monte Carlo exercise. Observational tests of the lens model are proposed, and the time delays between various pairs of images are determined, as the core of the source is known to be significantly variable. Future observations of the lens hold the key to using B1933+503 to constrain Hubble's constant. Despite the absence of a source redshift, the utility of the system as a probe of the structure of the lens galaxy is unparalleled as it provides a surfeit of easily identifiable constraints for modelling the system.     

B0712+472: a new radio four-image gravitational lens

A new four-image gravitational lens system, B0712+472, has been discovered during the Cosmic Lens All-Sky Survey. This system consists of four flat-spectrum radio images that are also seen on a Hubble Space Telescope ( HST ) image, together with the lensing galaxy. We present MERLIN, VLA and VLBA maps and WHT spectra of the system as well as the HST images. The light distribution of the lensing galaxy is highly elongated and so too is the mass distribution deduced from modelling. We suggest a redshift of ∼1.33 for the lensed object; the lens redshift will require further investigation. The discovery of this new system further increases the ratio of four-image to two-image lens systems currently known, exacerbating problems of required ellipticity of matter distributions in lensing galaxies.     

Implications of pre-mesozoic orogeny in the geological evolution of the Himalaya and Indo-Gangetic Plains

An integrated geological analysis of the Himalaya and Indo-Gangetic Plains demonstrates that the Great Vindhyan Basin incorporating large parts of these morphotectonic units were uplifted into an uneven landmass due to the Pre-Mesozoic orogenic cycle. This uneven landmass was eroded off largely during a considerable part of the Devonian and Carboniferous thereby causing partial absence of sedimentary sequences of these periods except in parts of the Tethys Himalaya. The Late Paleozoic epeirogenic movements brought about renewed sedimentation in the Lesser and Tethys Himalayas in the Krol and Tethys Basins, respectively, which was terminated by the Himalayan Orogeny during Late Cretaceous—Early Eocene.     

Use of Surface Observations to Estimate Upper Air Humidity for the Objective Analysis of Relative Humidity over Indian Region

In the present study objective analyses of relative humidity (RH) at surface and at the levels of 850,700 and 500 hPa have been made using Gandin’s (1963) optimum interpolation scheme. As the horizontal resolution of the radiosonde stations is rather inadequate for upper air humidity analysis, a scheme has been developed, following Rasmussen (1982) to estimate the upper air RH from the surface observations like surface RH, present weather and cloud cover. The relative humidities at the levels 850, 700 and 500 hPa were related to the surface observations through three separate regression relations. The RH values at 850, 700 and 500 hPa levels were estimated from the surface RH, cloud coverage and present weather using the above regression relations and subsequently the objective analyses at 00 GMT for the period from 4 July to 8 July 1979, were made using these estimated data along with the observed radiosonde data. Objective analyses were also made for the same period using only the radiosonde data for comparison to study the impact of those estimated data. Root mean square errors were computed for all the five days by interpolating RH at the observing stations from the objectively analysed field and comparing them with the actually observed RH to examine how best the analyses (with and without estimated data) fitted the observations. Lastly they were compared with satellite cloud pictures. This study shows that the estimated upper air RH values have positive impact on the analysis of upper air RH and could be used over radiosonde date sparse region and even over oceanic regions.     

Assessment of flexural analysis applied to the Sumatra-Java subduction zone

Indian Ocean subduction zone is one of the most active plate margins of the globe as evident from its vast record of great magnitude earthquake and tsunami events. We use Bouguer admittance (Morlet isostatic response function) in Sumatra-Java subduction zones comprising both the subduction and over-riding plates to determine the lithospheric mechanical strength variations. We determine effective elastic thickness (T _e ) for five oceanic windows (size 990 × 990 km²) by analyzing the admittance using Bouguer gravity and bathymetry data. The results show bimodal T _e values < 20 km for Sumatra and 20−40 km for Java. The lower bimodal values obtained for Sumatra appears to correlate well with the zones of historical seismicity. This is in sharp contrast with Java subduction zone, which shows higher T _e values (20–40 km) and apparently associated with low magnitude earthquakes. We suggest a strong and wide interseismic coupling for Sumatra between the subducting and over-riding plates, and deeper mantle contributing to low strength, shallow focus — high magnitude seismicity and vice versa for Java, leading to their seismogenic zonation.     

Spectral wave characteristics in the coastal waters of the central west coast of India during tropical cyclone Kyarr

Ocean Dynamics - The study presents the assessment of spectral wave conditions in the coastal waters of the central west coast of India based on data from waverider buoys at two locations during...     

Assigning a magmatically defined tectonic environment to Chitradurga metabasalts,India, by geochemical methods

The major and trace-element patterns in a set of 45 analyses of the Precambrian Chitradurga metabasalts have been interpreted by geochemical methods to classify the magma-types and to determine the tectonic environment of eruption.During amphibolitization of the tholeiites, the order of relative chemical stability is: SiO₂ > MgO > Al₂O₃ > FeO > CaO > Na₂O > K₂O > P₂O₅. On the ACFN plot the Chitradurga amphibolites approximate the unaltered basalts in their N component, show considerable depletion in F and A, and enrichment in the C components. With respect to the Keweenawan metadomains (pumpellyite and epidote), the Chitradurga amphibolites show considerable enrichment in N and depletion in the C constituents. The calc-alkaline (mol.props.) index, SiO₂ (wt.%) and “F”MA plots have shown the differentiation of the parent olivine normative tholeiite through the transitional calc-alkalic basalts to basaltic andesites; the ferrofemic index being 67.Discriminant functional analysis of the major-element patterns has classified the magma-types into ocean-floor basalts (9 analyses) and the volcanic arc series containing low-potassium tholeiites (24 analyses), calc-alkalic basalts (6 analyses) and basaltic andesites (6 analyses). The effective discrimination of the ocean-floor basalts from low-potassium tholeiites is accomplished due to the relatively low eigenvalues in functions F₁ and F₂ for SiO₂, K₂O and high values for MgO, TiO₂ in the former as compared to the latter. The low-K tholeiites are discriminated from calc-alkalic and basaltic andesites by the gradational increase in eigenvalues for K₂O, SiO₂ and Al₂O₃ in functions F₂ and F₃. The discriminant analyses of the trace-element patterns have classified the ocean-floor basalts from low-K tholeiites on TiCr, TiZr and Ti(× 10^?2)ZrY(× 3) plots. The TiO₂K₂OP₂O₅ plot has discriminated ocean-floor basalts, low-K tholeiites and the calc-alkalic group containing the basaltic andesite members. Thus the discriminant analysis of the major and trace-element patterns have shown noteworthy consistency, thereby attesting to the high success rate of classification.The Ca-Mg rich, low SiO₂, K₂O and alumina, olivine normative characteristics, and the normative pyroxene content of 36.15–45.88% of the ocean-floor basalts compare closely with those of the oceanic magma type of the Dalma volcanic suite of the north-eastern part of the Precambrian Indian shield of Bihar. These compositional features indicate their mantle origin, amphibolite and plagioclase—pyrolite assemblage of the upper mantle and relatively low-temperature, moderate pressure and hydrous environment of pyrolite.The presence of ocean-floor basalts at Chitradurga implies the existence of an oceanic rise and their eruption through its axial rift region. The mean Ti content (0.77%) of ocean-floor basalts compares closely with that of the Dalma suite (0.76%). The low-alumina content indicates faster spreading of the ocean floor.Identification of the magma-types of volcanic arc series containing a wide range of Zr and Y is attributed to quartz-normative fractionation of the magma and its differentiation to calc-alkalic and basaltic andesite members due to incorporation of sialic material by accretion in the marginal regions of the volcanic belt.Attention is focussed on the synonymous tectonic evolutionary trends of the two typical volcanic belts of the two geographically widely separated regions of the Indian Precambrian shield; the basis being: (1) low-alumina, enriched Ca-Mg and almost identical concentrations of Ti in the ocean-floor magma type, and (2) the presence of a pronounced volcanic arc magma type in the Chitradurga area and two analyses of a volcanic arc magma type in the Dalma area.     

Salinity-induced survival strategy of Vibrio cholerae associated with copepods in Cochin backwaters

The occurrence of Vibrio cholerae in water, sediment and copepods was studied over a wide range of salinity using conventional and polymerase chain reaction (PCR) techniques in the Cochin backwaters. V. cholerae occurred either as culturable or non-culturable form in this tropical estuary. During the pre monsoon period when high salinity prevailed (35.5psu) V. cholerae was associated with copepods only in non-culturable form, but with the onset of monsoon when lower salinity prevailed, copepod-associated-V. cholerae reverted back to culturable form. The optimum salinity range for culturability was found to be 15-20psu. This points to the fact that salinity is a major factor that which influences V. cholerae's culturability and its association with copepods in Cochin backwaters.     

Numerical Simulations of the Impacts of Land-Cover Change on a Southern Sea Breeze in South-West Western Australia

A sea-breeze event in south-west Western Australia is simulated using the Regional Atmospheric Modelling System (RAMS) version 6.0. The model is evaluated against high resolution soundings as well as station observations and is shown to reproduce the qualitative features of the sea breeze well. Sensitivity tests are carried out to investigate the effects of historical land-cover change and changes in soil moisture on the dynamics of the sea breeze. It is found that land-cover change alone, i.e., a change from wooded grasslands to bare soil, with no change in soil moisture initialisation, does not significantly alter the overall structure of the sea breeze but results in higher surface winds due to the reduced vegetation roughness length, which leads to enhanced surface moisture advection inland. On the other hand, land-cover change in conjunction with increased soil moisture results in a considerably weaker, shallower, and less penetrative sea breeze, and delays its onset and duration. A sea-breeze scaling analysis highlights the impact of increasing soil moisture on reducing the sea-breeze volume flux scale.