Fisher Matrix-based Predictions for Measuring the <Emphasis Type="Italic">z</Emphasis> = 3.35 Binned 21-cm Power Spectrum using the Ooty Wide Field Array (OWFA)

We use the Fisher matrix formalism to predict the prospects of measuring the redshifted 21-cm power spectrum in different k-bins using observations with the upcoming Ooty Wide Field Array (OWFA) which will operate at 326.5 MHz. This corresponds to neutral hydrogen (HI) at z = 3.35, and a measurement of the 21-cm power spectrum provides a unique method to probe the large-scale structures at this redshift. Our analysis indicates that a 5σ detection of the binned power spectrum is possible in the k range 0.05 ≤ k ≤ 0.3 Mpc^?1 with 1000 hours of observation. We find that the signal- to-noise ratio (SNR) peaks in the k range 0.1?0.2 Mpc^?1 where a 10σ detection is possible with 2000 hours of observations. Our analysis also indicates that it is not very advantageous to observe beyond 1000 h in a single field-of-view as the SNR increases rather slowly beyond this in many of the small k-bins. The entire analysis reported here assumes that the foregrounds have been completely removed.     

Pacific coral oxygen isotope and the tropospheric temperature gradient over the Asian monsoon region: a tool to reconstruct past Indian summer monsoon rainfall

Having recognized that it is the tropospheric temperature (TT) gradient rather than the land–ocean surface temperature gradient that drives the Indian monsoon, a new mechanism of El Niño/Southern Oscillation (ENSO) monsoon teleconnection has been unveiled in which the ENSO influences the Indian monsoon by modifying the TT gradient over the region. Here we show that equatorial Pacific coralline oxygen isotopes reflect TT gradient variability over the Indian monsoon region and are strongly correlated to monsoon precipitation as well as to the length of the rainy season. Using these relationships we have been able to reconstruct past Indian monsoon rainfall variability of the first half of the 20th century in agreement with the instrumental record. Additionally, an older coral oxygen isotope record has been used to reconstruct seasonally resolved summer monsoon rainfall variability of the latter half of the 17th century, indicating that the average annual rainfall during this period was similar to that during the 20th century. Copyright © 2011 John Wiley & Sons, Ltd.     

Evaluation of turbulent fluxes over Maitri,Antarctica

Turbulent fluxes have been evaluated for clear sunny days over the Indian Antarctic station, Maitri, using the basic meteorological data recorded at four levels of a 28 m tower. The data are supplemented with radiation data. The surface layer over Maitri remains thermally stratified during the hours of minimum solar insolation, the so-called nighttime period. The surface winds during this period are generally very strong resulting in high momentum fluxes. In particular, for high winds (>12 m s^–1), the temperature gradient is found to be less positive than for moderate winds (4 to 7 m s^–1). Solar insolation provided the daytime heating necessary for the diurnal variation of atmospheric stability, and hence, for the turbulent fluxes. Thus, on clear days daytime conditions are marked by upward transport of heat with reduced momentum flux, while stable nighttime conditions are marked by a downward heat flux with increased momentum fluxes.     

Acoustic sounder measurements of the planetary boundary layer at Maitri,Antarctica

The planetary boundary layer (PBL) over the Indian Antarctic station, Maitri (70.7° S; 11.7° E; 120 m asl) has been studied using a monostatic acoustic sounder. Acoustic sounder records reveal that the Antarctic PBL remains stably stratified throughout the year except for some periods in the peak summer months. The summertime PBL exhibits a diurnal variation with ground-based inversions developing at night and the convective plumes occurring during the peak sunlight hours. The cyclonic inflow of warm oceanic air towards the continent's interior from the coast helps in the development of the elevated layers and the Kelvin-Helmholtz waves observed on the sodar records.     

Simulation of diagenesis and permeability variation in two-dimensional rock structure

A model is suggested to simulate the physical aspect of diagenesis in porous rocks. A bidisperse ballistic deposition model with relaxation of deposited grains is used to generate the porous structure. Sedimentation and erosion are allowed to restructure the pore space as a fluid flows through the rock. The effect of this restructuring of the pore space on permeability is studied. The Navier–Stokes equation is solved numerically by the finite difference method to determine the pressure and velocity distributions in the pore space. We find that though deposition is the dominant process in our model of diagenesis, reducing the porosity, the permeability may increase dramatically in some cases. These are when the erosion takes place at a single narrow constriction in the pore channel.     

Land use indicators of a watershed in arid region, western Rajasthan using Remote Sensing and GIS

The vegetation dynamics and land use/land cover types of Birantiya Kalan watershed located in the arid tracts of western Rajasthan have been characterized and evaluated using Remote Sensing and Geographical Information System (GIS). The watershed under study falls in the transitional plain of Luni Basin and is characterized by Aravali ranges in the eastern half and vast alluvial plains in the west. The land use/land cover types, as identified are cropland, fallow, forest, land with scrub, land without scrub, sandy area and the water body. Land with scrub occupied maximum area (39% area of the watershed) in 1996 in place of crop land which was dominant (43% of total area) in the year 1988. During eight years period, seasonal fallow land increased significantly and the areal extent of water body decreased to almost half. Vegetation vigour types have been classified into very poor, poor. moderate, good and very good categories. Moderate vigour type reduced from 62 to 27% and poor type increased from 34 to 68% during the period 1988 to 1996. Other vegetation vigour types have not shown any significant changes. To quantify the changes over the years in both vegetation and land use/land cover, weightages have been given to each type and composite values of both vegetation vigour and land use types for 1996 and 1988 have been calculated. It has been observed that the ratio for vegetation vigour has been found to be 0.85 showing that the overall vegetation have not improved after the treatment. The ratio for land use is found to be 1.01, which indicates negligible change in land use.     

Cosmology and Astrophysics using the Post-Reionization HI

We discuss the prospects of using the redshifted 21-cm emission from neutral hydrogen in the post-reionization epoch to study our Universe. The main aim of the article is to highlight the efforts of Indian scientists in this area with the SKA in mind. It turns out that the intensity mapping surveys from SKA can be instrumental in obtaining tighter constraints on the dark energy models. Cross-correlation of the HI intensity maps with the Ly α forest data can also be useful in measuring the BAO scale.     

An experimental investigation to characterise soil macroporosity under different land use and land covers of northeast India

Saturated macropore flow is the dominant hydrological process in tropical and subtropical hilly watersheds of northeast India. The process of infiltration into saturated macroporous soils is primarily controlled by size, network, density, connectivity, saturation of surrounding soil matrix, and depthwise distribution of macropores. To understand the effects of local land use, land cover and management practices on soil macroporosity, colour dye infiltration experiments were conducted with ten soil columns (25 × 25 × 50 cm) collected from different watersheds of the region under similar soil and agro-climatic zones. The sampling sites included two undisturbed forested hillslopes, two conventionally cultivated paddy fields, two forest lands abandoned after Jhum cultivation, and two paddy fields, one pineapple plot and one banana plot presently under active cultivation stage of the Jhum cycle. Digital image analyses of the obtained dye patterns showed that the infiltration patterns differed significantly for different sites with varying land use, land cover, and cultivation practices. Undisturbed forest soils showed high degree of soil macroporosity throughout the soil profile, paddy fields revealed sealing of macropores at the topsoil due to hard pan formation, and Jhum cultivated plots showed disconnected subsoil macropores. The important parameters related to soil macropores such as maximum and average size of macropores, number of active macropores, and depthwise distribution of macropores were estimated to characterise the soil macroporosity for the sites. These experimentally derived quantitative data of soil macroporosity can have wide range of applications in the region such as water quality monitoring and groundwater pollution assessment due to preferential leaching of solutes and pesticides, study of soil structural properties and infiltration behaviour of soils, investigation of flash floods in rivers, and hydrological modelling of the watersheds.     

Analysing the spatio-temporal evolution of an active debris slide in Eastern Himalaya,India

Landslide is one of the prominent geohazards in the Himalayas where loss of lives and property are common. Owing to the complicated geomorphic and tectono-stratigraphic setting of this active Fold-thrust belt (FTB), landsliding of all possible types and spatial scales observed exhibit conspicuous spatio-temporal signatures and evolution. This evolution of landslides is commonly studied by regional assessment and by examining the multi-temporal landslide inventories of a particular area. The success of creating such multi-temporal landslide inventory depends on (i) the availability of relevant past source data (e.g., images, post event maps, air photos etc.) of suitable resolution, scale and quality, (ii) time of generation of source data with respect to the time of landsliding event, (iii) skill of the investigators in interpreting the old images, air photos etc. However, this method is of restricted use in studying the spatio-temporal evolution of a single landslide which is perennially active in the Himalayan terrain, where rapid changes in land use and land cover patterns readily obliterate the signatures of past landsliding. Moreover because of scale constraints, subtle and frequent changes in the spatial dimensions of these individual landslides, and their temporal activity become difficult to identify in such regional assessment carried out over a larger area. In this study therefore, a different approach is adopted whereby the spatio-temporal activity and style of Lanta Khola landslide, a perennially active and large (0.25 km²) debris flow in the Eastern Himalayas, has been studied in detail through detailed scale (1:1000) site-specific geological mapping in phases during the last 28 years (1983–2011). Such site-specific geological observations coupled with numerical slope stability analysis utilising the limit equilibrium method facilitate in detailed understanding of the temporal and spatial evolution and inherent mechanism of this perennial landslide.     

The chemical composition of tertiary Indian coal ash and its combustion behaviour – a statistical approach: Part 2

In Part 1 of the present investigation, 37 representative Eocene coal samples of Meghalaya, India were analyzed and their physico-chemical characteristics and the major oxides and minerals present in ash samples were studied for assessing the genesis of these coals. Various statistical tools were also applied to study their genesis. The datasets from Part 1 used in this investigation (Part 2) show the contribution of major oxides towards ash fusion temperatures (AFTs). The regression analysis of high temperature ash (HTA) composition and initial deformation temperature (IDT) show a definite increasing or decreasing trend, which has been used to determine the predictive indices for slagging, fouling, and abrasion propensities during combustion practices. The increase or decrease of IDT is influenced by the increase of Fe₂O₃, Al₂O₃, SiO₂, and CaO, respectively. Detrital-authigenic index (DAI) calculated from the ash composition and its relation with AFT indicates Sialoferric nature of these coals. The correlation analysis, Principal Component Analysis (PCA), and Hierarchical Cluster Analysis (HCA) were used to study the possible fouling, slagging, and abrasion potentials in boilers during the coal combustion processes. A positive relationship between slagging and heating values of the coal has been found in this study.