Polarization observations of the radio cores of AGN — I. A sample of quasars

We present total-intensity and linear-polarization observations at a single epoch for a sample of 11 quasars and one BL Lac object. The data were taken with the VLA A array at λλ 20, 18, 6 and 2 cm. We examine the variation of the degree of polarization, p , and polarization position angle, PA, with wavelength, and attempt to determine the rotation measure, RM, of the cores in these sources. The degree of polarization does not exhibit any systematic variation with wavelength, the median values ranging from 2.3 to 3.5 per cent at the different wavelengths. The variation of PA with λ² is not linear over the entire wavelength range. However, for most sources the λλ 20-, 18- and 6-cm PAs do follow such a linear relationship, yielding a median |RM| of about 15 rad m⁻². In contrast, the λλ 6- and 2-cm observations give a median |RM| of about 129 rad m⁻². The long-wavelength emission is likely to originate from a spatially different part of the milliarcsec-scale jet from the λ 2-cm emission, which could turn over at a higher frequency and is likely to be more compact and located closer to the quasar nucleus. We have attempted to obtain linear fits over the entire wavelength range allowing for n  π ambiguities in the PAs, but the fits are not statistically significant. The low values of RM for these core-dominated sources suggest that either the radio emission from the jet intercepts few of the emission-line clouds and their confining medium, or the clouds have a small filling factor and are possibly magnetically confined.     

Glacial mass balance changes in the Karakoram and Himalaya based on CMIP5 multi-model climate projections

The impact of future climate change on the glaciers in the Karakoram and Himalaya (KH) is investigated using CMIP5 multi-model temperature and precipitation projections, and a relationship between glacial accumulation-area ratio and mass balance developed for the region based on the last 30 to 40 years of observational data. We estimate that the current glacial mass balance (year 2000) for the entire KH region is -6.6?±?1 Gta^?1, which decreases about sixfold to -35?±?2 Gta^?1 by the 2080s under the high emission scenario of RCP8.5. However, under the low emission scenario of RCP2.6 the glacial mass loss only doubles to -12?±?2 Gta^?1 by the 2080s. We also find that 10.6 and 27 % of the glaciers could face ‘eventual disappearance’ by the end of the century under RCP2.6 and RCP8.5 respectively, underscoring the threat to water resources under high emission scenarios.     

Seasonal prediction of summer monsoon rainfall over cluster regions of India

Shared nearest neighbour (SNN) cluster algorithm has been applied to seasonal (June–September) rainfall departures over 30 sub-divisions of India to identify the contiguous homogeneous cluster regions over India. Five cluster regions are identified. Rainfall departure series for these cluster regions are prepared by area weighted average rainfall departures over respective sub-divisions in each cluster. The interannual and decadal variability in rainfall departures over five cluster regions is discussed. In order to consider the combined effect of North Atlantic Oscillation (NAO) and Southern Oscillation (SO), an index called effective strength index (ESI) has been defined. It has been observed that the circulation is drastically different in positive and negative phases of ESI-tendency from January to April. Hence, for each phase of ESI-tendency (positive and negative), separate prediction models have been developed for predicting summer monsoon rainfall over identified clusters. The performance of these models have been tested and found to be encouraging.     

Enhancement techniques for landuse analysis

In image interpretation, to make maximum use of the available information, some sort of enhancement is usually needed. In image enhancement, the aim is to manipulate the image to improve its quality. Image enhancement techniques emphasize upon the viewing of the image for extraction of information that may not have been so readily apparent in the original. Hera the software package for various enhancement techniques that has been developed at National bemote Sensing Agency (NRSA) is described. In order to illustrate the utility of the techniques, the enhanced imagery have been analysed for land use categories and linear features, and the corresponding thematic maps have also been shown in the results.     

Reconstruction of the moraine dammed lake,based on field evidence and paleo-history,Samudra Tapu Glacier,Chandra Basin,Himachal Pradesh

Peri-glacial studies of the Samudra Tapu glacier reveal three stages of well preserved moraines which are also marked by fluvial overprinting. The signatures of fluvial outwashes over the otherwise morainal deposits have been utilized in estimating the extent of palaeo-lake in the valley of Samudra Tapu glacier of the Chandra basin. Distance and thickness of snout of the glacier and its morainal deposits is estimated by the Laser Range Finder. With the change in the position of the snout there is a change in the extent and orientation of the lake. Recent expedition to the glacier confirms this process to be continuing. The study is important in reconstructing formation of the lake with respect to snout position of the glacier. Based on ground truth, fast melting of the snout is confirmed from year 2004 onwards, with the development of fresh end/terminal moraine. The study reveals that the snout region of the Samudra Tapu glacier is thinning and retreating at an alarming rate and is enlarging the lake extent. The development of fresh terminal moraine has the potential to impound the fast melting glacial waters which in turn can pose serious threat to the downstream regions of the Chandra valley.     

Recession of samudra tapu glacier, chandra river basin, Himachal Pradesh

Himalayas possess one of the largest resources of snow, ice and glaciers that act as a huge freshwater reservoir. Monitoring the glaciers is important to assess the overall reservoir health of the Himalayas. Samudra Tapu is one of the largest glaciers in Chandra basin of district Lahaul and Spiti, Himachal Pradesh. Based on the field investigations and the remote sensing techniques. features such as accumulation area, ablation area snowline/equilibrium line, moraine-dammed lakes and permanent snowfields were mapped. The glacial terminus was identified using moraine-dammed lake, as lake is located at down streamside of the terminus. The total recession of glacier during the period of 38 years (1962–2000) is about 742 m with an average rate of 19.5 m/yr. In addition, glacial extent is reduced from 73 to 65 km² between 1962 and 2000. suggesting overall deglaciation of 11%. During field investigation. three stages of glaciation using terminal moraine were identified. These moraines were mapped by merging LISS-II1 and PAN data. At the peak of glaciation. the glacial terminus was extended 3.18 km downstream of terminus position in year 2000. Total area during peak of glaciation period has been observed to be 77.67 km², which is 12.67 km² higher than the present glacier extent.     

Projected changes in South Asian summer monsoon by multi-model global warming experiments

South Asian summer monsoon (June through September) rainfall simulation and its potential future changes are evaluated in a multi-model ensemble of global coupled climate models outputs under World Climate Research Program Coupled Model Intercomparison Project (WCRP CMIP3) dataset. The response of South Asian summer monsoon to a transient increase in future anthropogenic radiative forcing is investigated for two time slices, middle (2031–2050) and end of the twenty-first century (2081–2100), in the non-mitigated Special Report on Emission Scenarios B1, A1B and A2 .There is large inter-model variability in the simulation of spatial characteristics of seasonal monsoon precipitation. Ten out of the 25 models are able to simulate space–time characteristics of the South Asian monsoon precipitation reasonably well. The response of these selected ten models has been examined for projected changes in seasonal monsoon rainfall. The multi-model ensemble of these ten models projects a significant increase in monsoon precipitation with global warming. The substantial increase in precipitation is observed over western equatorial Indian Ocean and southern parts of India. However, the monsoon circulation weakens significantly under all the three climate change experiments. Possible mechanisms for the projected increase in precipitation and for precipitation–wind paradox have been discussed. The surface temperature over Asian landmass increases in pre-monsoon months due to global warming and heat low over northwest India intensifies. The dipole snow configuration over Eurasian continent strengthens in warmer atmosphere, which is conducive for the enhancement in precipitation over Indian landmass. No notable changes have been projected in the El Niño–Monsoon relationship, which is useful for predicting interannual variations of the monsoon.     

Efficiency of Severe Recorded Rainstorms over Maharashtra State

12 severe rainstorms have been experienced by different meteorological sub-divisions of Maharashtra State during the last 100-year period from 1891-1990. For each of the rainstorms efficiency factors (i.e. P/ M ratios) were worked out for maximum one-day duration and for three standard areas of 1000, 5000, and 10,000 km2. Comparison of these ratios with the past has shown that the most efficient rainstorm over Maharashtra was the rainstorm of June, 1908 over the Vidarbha region whose full DAD data as well as isohyetal pattern have been given.