Observed intraseasonal and seasonal variability of the West India Coastal Current on the continental slope     

P Amol  D Shankar  V Fernando  A Mukherjee  S G Aparna  R Fernandes  G S Michael  S T Khalap  N P Satelkar  Y Agarvadekar  M G Gaonkar  A P Tari  A Kankonkar  S P Vernekar 《Journal of Earth System Science》2014,123(5):1045-1074

We present current data from acoustic Doppler current profilers (ADCPs) moored on the continental slope off the west coast of India. The data were collected at four locations (roughly at Kanyakumari, Kollam, Goa, and Mumbai) extending from ～ 7° to ～ 20°N during 2008–2012. The observations show that a seasonal cycle, including an annual cycle, is present in the West India Coastal Current (WICC); this seasonal cycle, which strengthens northward, shows considerable interannual variability and is not as strongly correlated along the coast as in climatologies based on ship drifts or the altimeter. The alongshore decorrelation of the WICC is much stronger at intraseasonal periods, which are evident during the winter monsoon all along the coast. This intraseasonal variability is stronger in the south. A striking feature of the WICC is upward phase propagation, which implies an undercurrent whose depth becomes shallower as the season progresses. There are also instances when the phase propagates downward. At the two southern mooring locations off Kollam and Kanyakumari, the cross-shore current, which is usually associated with eddy-like circulations, is comparable to the alongshore current on occasions. A comparison with data from the OSCAR (Ocean Surface Currents Analyses Real-time) data product shows not only similarities, but also significant differences, particularly in the phase. One possible reason for this phase mismatch between the ADCP current at 48 m and the OSCAR current, which represents the current in the 0–30 m depth range, is the vertical phase propagation. Current products based on Ocean General Circulation Models like ECCO2 (Estimating the Circulation and Climate of the Ocean, Phase II) and GODAS (Global Ocean Data Assimilation System) show a weaker correlation with the ADCP current, and ECCO2 does capture some of the observed variability.  相似文献   

Application of indigenous microbial consortia in bioremediation of oil-contaminated soils     

S. Shankar  C. Kansrajh  M. G. Dinesh  R. S. Satyan  S. Kiruthika  A. Tharanipriya 《International Journal of Environmental Science and Technology》2014,11(2):367-376

Bioremediation of oil spillage in soils using consortia of microbes beckons much exploration. The present study involves bioremediation of oil-contaminated soils from north Chennai, India, using indigenous microbial consortia. Totally, 32 positive oil degrading isolates were obtained from 3 different locations, i.e., petrol filling stations, automobile workshops and oil refineries. Substrate utilization patterns of individual isolates and the consortial sets were observed. Mixture of three common hydrocarbons (petrol, diesel and engine oil) was used for studies. The substrate oil utilized by consortia was taken for thin-layer and column chromatography which perfectly resulted in varied fractions of oil compared to the unused oil as control. The best consortia were used directly for bioremediation experiment. Three different oil-contaminated soils were used and bioremediation patterns were observed. The rate of bioremediation differed within soils, nevertheless all soils were almost 100 % reclaimed within 30 days. Bioremediation kinetics showed that the process corresponds to first-order kinetics and kinetic constants for the different soils ranged from 0.051 to 0.077/day. Assessment of detoxification of acute phytotoxicity owing to the pollutant oil was done, and results observed were significant. An increase of 25, 300 and 212 % in germination index, average growth index and sustenance index, respectively, of Trigonella foenum-graecum Linn. in treated soils was observed, compared to untreated soils. Thus, this study confirmed that microbes in ‘Consortial Union’ serve as better treating agents in bioremediation of oil-contaminated soils than individual microorganisms.  相似文献   

Study of Extended Radio Galaxies at 151.6 MHz using the Mauritius Radio Telescope     

Radhakhrishna Somanah  N. Udaya Shankar 《Astrophysics and Space Science》2002,282(1):57-67

The MRT survey will be by far one of the most extensive survey at low frequencies. This survey will provide a moderately deep radio catalog reaching a source density of about 2 × 10⁴ sr^-1over the southern sky with an angular resolution of 4' × 4' and a limiting flux density of 70 mJy (1 σ) at 151 MHz. The availability of zero spacing and short baselines in the MRT array will make it sensitive to the background temperature and to large scale features in the sky. In addition to this feature, the low frequency operation makes a study of continuum emission from large radio sources by MRT to have several interesting and important implications in the study of radio galaxies. This paper discusses the parameter space of radio galaxies which can be explored using the MRT. Images of a few extended radio galaxies are also presented. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Cosmic expansion driven by real scalar field for different forms of potential     

Murli Manohar Verma  Shankar Dayal Pathak 《Astrophysics and Space Science》2014,350(1):381-384

We discuss the expansion of the universe in the FRLW model assuming that the source of dark energy is either tachyonic scalar field or quintessence. The tachyonic scalar field with exponential and power-law potential (function of homogeneous scalar field ?) both gives exponential expansion of the universe. It is found that this behaviour is not distinguishable from the quintessence with respect to these potentials.  相似文献   

Estimating boundary currents from satellite altimetry: A case study for the east coast of India   总被引：1，自引：0，他引：1  

Fabien Durand  Doraiswamy Shankar  Florence Birol  S. Satheesh Chandra Shenoi 《Journal of Oceanography》2008,64(6):831-845

We present a methodology to derive surface geostrophic current from a newly released altimetric sea-level data set. TOPEX/Poseidon data were first completely reprocessed from Geophysical Data Records using new algorithms accommodating marginal seas and coastal conditions. The methodology applied to the reprocessed data essentially consists of a smoothing of the raw along-track coastal altimetric data at scales at which the geostrophic equilibrium holds. This was reduced to a computational procedure using a set of objective criteria. We have applied the method to the East India Coastal Current (EICC) at the western boundary of the Bay of Bengal. This paper first examines the quality of the new data set, which compares well with tide-gauge data; the current we derived is consistent with independent estimates. Our methodology reveals the full spectrum of the along-shore current, ranging from intra-seasonal to inter-annual time scales, from the deep ocean to the shelf-break area where the EICC exists. The algorithm can be applied to any coastal region where an order of the Rossby radius can be defined, and it therefore opens up bright prospects for mapping the variability of other boundary-current systems in the world ocean from altimetry.  相似文献   

Influence of spatially random soil on lateral thrust and failure surface in earth retaining walls     

Udit Shankar Dasgupta  Vinay Bhushan Chauhan 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2017,11(3):247-256

The present study investigates the influence of spatial variability of soil properties on the lateral thrust and failure surface of a 6?m high frictionless rigid earth retaining wall in active condition. The drained friction angle of the soil is modelled as a log-normal anisotropic random field in two dimensions, using the Cholesky decomposition technique. The effect of horizontal and vertical scale of fluctuation is observed on the lateral thrust. The failure surface in the backfill is found to be more or less similar for different combinations of spatial variability in vertical and horizontal directions. Monte-Carlo simulation technique is used to compute the probability of failure and to obtain the worst-case spatial variability configuration.  相似文献   

Heave Studies on Fly Ash-Stabilised Expansive Clay Liners     

B. R. Phanikumar  M. Uma Shankar 《Geotechnical and Geological Engineering》2017,35(1):111-120

Clay liners or compacted earthen barriers are important barrier materials used for preventing contaminant transport through soils. A low hydraulic conductivity (k) is a significant parameter that governs the design and construction of clay liners. Compacted expansive clays, which are montmorillonite clays, also have a very low hydraulic conductivity (k). When expansive clays are blended with fly ash, an industrial waste, the hydraulic conductivity (k) further reduces as the ash-clay blends result in increased dry densities at increased fly ash contents. Hence, fly ash-stabilised expansive clay can also be proposed as a unique clay liner material. As expansive clays undergo heave when they come into contact with water, it is necessary to study the heave behaviour of fly ash-stabilised expansive clay liners. This paper presents heave studies on fly ash-stabilised expansive clay liners. Fly ash in different contents by dry weight of the expansive clay was added to the clay, and the ash-clay blend was compacted as a liner overlying a natural field soil layer. Compacted lateritic clay was used for simulating the natural field soil into which contaminants migrate. Calcium chloride (CaCl₂) solution of varying concentration (5, 10, 20, 50, 100 and 500 mM) was used as the permeating fluid in the heave studies. The rate of heave and the amount of heave of the fly ash-stabilised expansive clay liners were monitored. Deionised water (DIW) was also used as inundating fluid for comparative study. Heave (mm) decreased with increase in solute concentration for all fly ash contents. For a given solute concentration, heave decreased up to a fly ash content of 20 % and thereafter it increased when the fly ash content was increased to 30 %. Heave of the fly ash-stabilised expansive clay liners was correlated with their permeability, liquid limit (LL) and free swell index (FSI) pertaining to the respective fly ash content and CaCl₂ concentration.  相似文献   

Environmental and social recovery asymmetries to large-scale disturbances in small island communities     

Aswani  Shankar  van Putten  Ingrid  Miñarro  Sara 《Natural Hazards》2017,86(1):241-262

Natural Hazards - People’s livelihoods in tropical small-island developing states are greatly dependent on marine ecosystem services. Yet services such as fisheries and coastal buffering are...  相似文献   

Vulnerability of groundwater in an industrial (Bauxite) valley of Lanjigarh (Orissa), India     

Vijay Shankar Singh  Ranjeet Kumar Prasad  Pallavi Banerjee 《Environmental Earth Sciences》2010,60(8):1739-1751

Groundwater, particularly in the shallow zone aquifer is an easily available source of freshwater that serves various needs of people around it. Due to rapid growth in the industrial sector, the shallow groundwater regime becomes vulnerable to industrial toxicity and human activity. In the case of bauxite ore processing industry it is not only the groundwater potential that gets affected, but often the quality of groundwater is at risk from the ore processing activity. Bauxite processing plant has been setup in the Lanjigarh (Orissa State), India during 2007. An attempt has been made to evaluate the groundwater regime in the watershed that comprises the plant and its various disposal sites. Although the groundwater has not been found affected due to waste disposals, however, areas vulnerable to pollution have been demarcated.  相似文献   

Vertical propagation of baroclinic Kelvin waves along the west coast of India     

D. Nethery  D. Shankar 《Journal of Earth System Science》2007,116(4):331-339

A linear, continuously stratified ocean model is used to investigate vertical propagation of remotely forced, baroclinic Kelvin waves along the Indian west coast. The extent of vertical propagation over the length of the coast is found to be an increasing function of the forcing frequency. Simulations show that, over the length of the Indian west coast, vertical propagation is limited at annual and semi-annual periods, but significant at periods shorter than about 120 days. This has two major consequences. First, the depth of subsurface currents associated with these frequencies varies substantially along the coast. Second, baroclinic Kelvin waves generated in the Bay of Bengal at periods shorter than about 120 days have negligible influence on surface currents along the north Indian west coast.  相似文献