Automated Detection of Solar Radio Bursts Using a Statistical Method

Solar Physics - In early September 2017, a series of solar flares and coronal mass ejections (CMEs) erupted from the Sun. The Cor2a coronagraph, a unit of the Sun Earth Connection Coronal and...     

Seismic quality factor observations for gas-hydrate-bearing sediments on the western margin of India

Any propagating wave undergoes attenuation, which is primarily governed by the physical properties of the medium, determined in terms of quality factor (Q). Research into the characteristics of both P- and S-wave Q with reference to gas-hydrates exploration remains in its infancy. Presence of gas-hydrates increases the Q, and this again depends on the nature of distribution and amount of hydrates within the sediments. Thus, estimation of Q provides useful input for both the detection and quantitative assessment of gas-hydrates. Here we propose a simple technique of deriving Q from prestack surface seismic reflection data based on the logarithm of spectral ratio (LSR), and apply the method to marine multi-channel seismic (MCS) data collected on the western margin of India where a bottom simulating reflector (BSR), which is a prime marker for gas-hydrates, has already been identified. The Q (256 ± 11) estimated over the region with a strong BSR is found to be more than double the Q (101 ± 9) derived for the region without any BSR or a weak BSR. The anomalously high Q with respect to the background can be used to detect gas-hydrates in areas where the BSR is not very clearly observed on seismic sections.     

Solar dynamics imaging system a back-end instrument for the proposed NLST

The Solar Dynamics Imaging System (SDIS) will be one of the focal plane instruments operated at the National Large Solar Telescope (NLST). The prime objective of the instrument is to obtain high spatial and temporal resolution images of the region of interest on the Sun in the wavelength range from 390 nm to 900 nm. The SDIS provides filtergrams using broad-band filters while preserving the Strehl ratio provided by the telescope. Furthermore, the SDIS is expected to provide observations that allow image reconstruction to extract wave front information and achieve a homogenous image quality over the entire FOV.     

A MATLAB™ code to perform weighted linear regression with (correlated or uncorrelated) errors in bivariate data

MATLAB™ is a powerful, easy to use, software package suitable for many mathematical operations, which finds plenty of scientific applications. One such application is the fitting of trend lines for a given data set so as to interpret the relationship of the variance of the parameters involved. We provide here a code in MATLAB™ that performs the weighted linear regression with (correlated or uncorrelated) errors in bivariate data which can handle ‘force-fit’ regression as well.     

Playa sediments of the Didwana Lake,Rajasthan: A new environment for surficial-type uranium mineralisation in India

The Didwana playa, the second largest playa in the eastern part of the Thar desert, is 5.6 km long and 2.4 km wide and supports commercial salt production. The thickness of lake sediment package is reported to be 20 m and comprises fine grained clays and silts, with abundant calcite, gypsum, and halite, associated with hypersaline water. Isolated hills of graphitic phyllite and quartzite are seen on the western side of the lake. During the course of investigations for uranium in surficial environment of semi-arid terrain of Rajasthan, ground water sampling defined a NE-SW trending uranium halo encompassing the Didwana playa. Subsequent sampling of unlined dug wells, up to water table in central part of the playa, indicated uranium values up to 190 ppm and 2072 ppb in lake sediments and brine respectively. These values are of the order of 21 ppm and 192 ppb towards the southwestern periphery of the lake. The average uranium content, as inferred from 12 samples in the central part of the lake, is around 60 ppm over a thickness of 5 m. It appears that the uranium is loosely bonded to the sediments in amorphous form and is, hence, easily leachable. Samples of brine (n=10), from both the central and southwestern portions of the lake, analysed high (1,67,500–3,00,000 mg/l) TDS, HCO₃⁻ (1128–8395 mg/l), and SO₄ (30,536–88,000 mg/l). These are of alkaline (pH: 7.2–9.3) and reducing (Eh: −200 to −340 mV) nature. Under these Eh-pH conditions below the groundwater table, and for such uranium bearing groundwater, precipitation of primary uranium is expected. It is, therefore, modelled that uranium in lake sediment package above water table is concentrated by evaporation process and by chemical reduction below the water table.     

Intra-annual variations of teak cellulose ��18O in Kerala, India: implications to the reconstruction of past summer and winter monsoon rains

A seasonal cycle has been observed in the high and coarse resolution intra-annual analyses of oxygen isotopic composition (??¹⁸O) of teak (Tectona grandis) cellulose from southern India, that receives both the south-west (SW) (summer) and the north-east (NE) (winter, more depleted in ¹⁸O) monsoon rains. The seasonal cycle as recorded by teak, with an amplitude between 1 and 3??, shows lower ??¹⁸O values at the early and late growing seasons than at the middle. This pattern is opposite to that found in central Indian teak, nurtured mostly by the SW monsoon rain. A comparison of the observed and modeled intra-annual profiles reveals that the observed pattern of intra-annual ??¹⁸O variation in southern India is explainable only if teak trees had sampled rainfall from both the monsoons. Thus it appears possible to detect years of past excess NE monsoon rains by analyzing the ??¹⁸O of cellulose from the latewood of teak trees growing in Kerala, southern India.     

Geomagnetic disturbances associated with disappearing solar filaments

To gain an insight into the origin of enhanced geomagnetic activity that is recently reported to follow the disparition brusque (DB) of quiescent solar filaments, a study is made of the interplanetary plasma and magnetic field data at 1 AU, in relation to DBs over the period January 1967 through March 1978. The investigation revealed that the minor (Ap 30) and major (Ap 50) geomagnetic disturbances that manifested within 8 days of DBs, almost invariably occurred (in 28 out of the 30 events studied) in association with the passage at Earth of high-speed streams in the solar wind. A majority of the streams (19 out of the 28 streams) exhibited a 27-day recurrence pattern and, thus, the associated enhancement in geomagnetic activity (and apparently followed DBs). The date of transit of the high-speed stream at Earth seems to control the delay time of the geomagnetic disturbance, rather than the size of the filament. A systematic spatial relationship between DB's and the potential solar sources of the high-speed streams (coronal holes and flares) does not appear to be present. The results point out the relevance and a prominent role of recurrent and transient high-speed structures in the solar wind in the enhancement of geomagnetic activity that accompagnies DBs.     

Coastal hazard mapping in the Cuddalore region, South India

It is estimated that nearly one-third of India’s population lives on the coast and is dependent on its resources. Shoreline erosion, storm surges and extreme events have resulted in severe loss of human life, damage to ecosystems and to property along the coast of India. Studies carried out in the Cuddalore region of South India reveal that this low-lying coastal zone, which suffered significant erosion during the last century, has been severely affected by the tsunami of 2004, storm floods and cyclones. In response to these impacts, a variety of coastal defense measures and adaptation strategies have been implemented in the region, although with only limited success. In order to inform future coastal planning in this region, the work reported here identifies a composite hazard line, seaward of which coastal flooding events will have a return interval of less than 1 in 100 years. The area landward of the coastal hazard line will be unaffected by 100 years of coastal erosion at present day rates. The study directly supports the Integrated Coastal Zone Management (ICZM) Plan of the Tamil Nadu State through the identification and assessment of coastal hazards and the overall vulnerability to coastal flooding and erosion. The key results from this pilot study will be used directly by the State of Tamil Nadu in the protection of the coastal livelihoods, better conservation measures and sustainable development along the coast. This study is a step toward mapping the hazard line for the entire coast of India that helps protect human lives and property.     

Study of hydrogeochemical processes of the groundwater in Ghatprabha river sub-basin, Bagalkot District, Karnataka, India

The alluvial aquifer of the Ghatprabha River comprises shallow tertiary sediment deposits underlain by peninsular gneissic complex of Archean age, located in the central–eastern part of the Karnataka in southern India. In order to establish the baseline hydrochemical conditions and processes determining the groundwater quality, groundwater samples were collected as part of an integrated investigation that coupled multivariate statistical analysis with hydrochemical methods to identify and interpret the groundwater chemistry of the aquifer system. Three main hydrochemical types (Ca–Mg–Cl, Ca–Mg–HCO₃, and Na–SO₄) were identified. Gibbs plots indicate that the evolution of water chemistry is influenced by water–rock interaction followed by evapotranspiration process. The results of factor analysis indicated the total variance explained by the extracted factor 79.9% and 87.1% for both pre- and post-monsoon, respectively. And other processes such as silicate weathering, ion exchange, and local anthropogenic activities affect the groundwater chemistry.