Seismic attribute study for gas hydrates in the Andaman Offshore India

Seismic data from the Andaman offshore region has been examined to investigate for the presence of gas hydrates. The seismic data displays reflection characteristics such as blanking, enhanced reflection patterns, shadows in instantaneous frequency, and increase in amplitude with the offset, which are indicative of gas hydrates and underlying free gas. A prominent bottom-simulating reflection, BSR, coupled with reverse polarity is observed around 650–700 ms. Seismic attributes such as the reflection strength and instantaneous frequency are computed along this reflector in order to probe for the presence of gas hydrates or free gas in this region. The reflection plot shows a strong reflector paralleling the seafloor. In addition, attenuation of the high frequency signal is noticed, indicating the presence of free gas below the BSR.     

Spectral characteristics of high shallow water waves

The spectral characteristics of shallow water waves with significant wave height more than 2 m based on the data collected along the Indian coast is examined. It was found that the value of Joint North Sea Wave Project (JONSWAP) parameters (α and γ) increases with significant wave height and mean wave period and decreases with spectral peak period. The estimated average value (0.0027 and 1.63) of the JONSWAP parameters, α and γ were less than the generally recommended values of 0.0081 and 3.3, respectively. By carrying out a multi-regression analysis, an empirical equation is arrived relating the JONSWAP parameters with significant wave height, peak wave period and mean wave period. It was found that the Scott spectra underestimate the maximum spectral energy of high waves. The study shows that the measured wave spectra can be represented by JONSWAP spectra with the JONSWAP parameters estimated based on the equation proposed in this paper.     

Signature of the 27-day variation in hemispheric sunspot activity and asymmetry during 2010-2015

In the present work,we study the time evolution,significance of the N-S asymmetry excesses presented as a function of the solar cycle and prominent rotational p...     

GIS based spatial data analysis for landslide susceptibility mapping

Landslide susceptibility map delineates the potential zones for landslides occurrence. The paper presents a statistical approach through spatial data analysis in GIS for landslide susceptibility mapping in parts of Sikkim Himalaya. Six important causative factors for landslide occurrences were selected and corresponding thematic data layers were prepared in GIS. Topographic maps,satellite image,field data and published maps constitute the input data for thematic layer preparation. Numerical weights for different categories of these factors were determined based on a statistical approach and the weighted thematic layers were integrated in GIS environment to generate the landslide susceptibility map of the area. The landslide susceptibility map classifies the area into five different landslide susceptible zones i.e.,very high,high,moderate,low and very low. This map was validated using the existing landslide distribution in the area.     

Chemistry of springwater in Almora, Central Himalaya, India

 A field study was conducted to assess variations in physico-chemical characteristics of water of the springs located within the boundary of a Central Himalayan town where the springwater is used for drinking purposes. Monitoring of 12 springs was carried out for three seasons (winter, summer and monsoon). The results indicate direct influence of unplanned sewage disposal on the springwater quality as reflected by significant regional variations in the concentration of nitrates, chlorides, sulfates, sulfides and electrical conductivity. Population density varies within the town from 3110 to 14 137 persons/km^–2 and has direct relationship with water quality. Springs located in the densely populated area had higher concentrations of all these compounds. Concentrations of nitrates up to 60 ppm were observed in some springs, making water unsuitable for human consumption. No significant changes were observed in springwater quality during different seasons. Received: 3 February 1995 · Accepted: 27 February 1996     

Identification of AlF Molecular Lines in Sunspot Umbral Spectra

High resolution FTS sunspot umbral spectra from NSO/Kitt Peak were used to detect rotational lines due to 11 electronic transitions of the molecule AlF, in the wavelength region 4400 – 9000 Å. The presence of lines due to bands C – A (0,0), (0,1), (0,2) and (1,2), D – A (0,0) and (0,1), F – A (0,0), G – A (0,0), and F – B (0,0) is confirmed. Further, the presence of lines due to C – A (1,0) and (1,1) transitions is treated as doubtful because of heavy blending in the region, by rotational lines of TiO. Among the identified lines, those which are well resolved were selected for measurement of equivalent widths. The measured values for the bands D – A (0,0) and F – A (0,0) were used to estimate the respective effective rotational temperatures to be 1240 ± 120 K and 2390 ± 400 K.     

On the formation of Jupiter

Arguments are presented to show that Jupiter could not have been formed as a star of mass 0.001M and that the observed excess energy is not due to gravitational contraction from an extended, gaseous state.     

Analysis of Y-component of Geomagnetic Field and SYM-H Index Using Wavelet Multiresolution Analysis

Geomagnetism and Aeronomy - Electrodynamical coupling between the solar wind’s plasma and the Earth’s magnetosphere creates geomagnetic disturbances recorded on the ground. This work...     

Constraining probabilistic chloride mass-balance recharge estimates using baseflow and remotely sensed evapotranspiration: the Cambrian Limestone Aquifer in northern Australia

Hydrogeology Journal - Regional-scale estimates of groundwater recharge are inherently uncertain, but this uncertainty is rarely quantified. Quantifying this uncertainty provides an understanding...     

DInSAR-based monitoring of land subsidence related to groundwater over-exploitation: example from developing urban center of Nairobi,Kenya

Over-exploitation of groundwater in many evolving urban settings causes ground subsidence and permanent loss of aquifer storage capacity. DInSAR (differential interferometric synthetic aperture radar) time series data from 2016 to 2019 were used to monitor and model the surface deformation around Nairobi, Kenya, where the water demand has exceeded the supply without capacity augmentation for over two decades. The aquifer system constitutes hard rock to semiconfined ash beds in volcanic terrain. The Small Baseline DInSAR technique identified the spatial pattern of subsidence and magnitude (line-of-sight (LOS) velocity), which exceeds 41 mm/year in the semiconfined aquifer towards the western-central part of Nairobi. The spatial distribution of subsidence is consistent with the groundwater level drop and probable compaction modeled using aquifer characteristics for 1950–2015. The Global Navigation Satellite System (GNSS) data at a station from 2007 to 2018 indicate a cumulative 4-cm subsidence which is comparable to ~2.5-cm LOS subsidence from the present study for 2016–2019. The correlation with other hydrological data suggests the aquifer is experiencing inelastic subsidence due to unsustainable groundwater extraction, putting a massive strain on Nairobi’s aquifer system. The present DInSAR based study establishes its effectiveness in the monitoring of groundwater over-exploitation-based subsidence and associated hazard to the aquifer in emerging urban centers.