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81.
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
82.
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
83.
Frequency-domain electromagnetic sensing can be an effective tool for ascertaining subsurface water dynamics. In California, the paucity of available irrigation water, recurrence of drought and presence of indigenous salts within the geological parent materials affect crop health. Subsurface leaching variability analyses were performed using dual dipolar induction surveys and stochastic computations to determine salinity conditions conducive to plant growth. Soils in the study area had randomly variable salinity with elevated salt levels within the substratum. The salinity values were mostly above 300 mS m?1 and some areas exceeded the 1500 mS m?1 level. The leaching conditions across the fields varied generally from 5 to 50%. Both variables showed slightly positive skewness with minutely asymmetrical tailing. The salinity distribution had less peakedness than the leaching distribution. Albeit with spatially dependent variability and skewness, the distribution patterns had low errors. There was a strong and significant correlation (r?=?0.939 at P?<?0.05) between the observed and predicted conductivity data. The leaching variables exhibited directional dependence along vertical and horizontal gradients. Spatial increase in salinity within the substratum conformed to salt leaching and water percolation processes. All observed salinity values within the substratum exceeded salt tolerance threshold limits for major crops and favorable leaching conditions were observed at low salinity levels. Sustainability of agriculture in California is heavily dependent on adequate water use planning and our approach of leaching variability analyses can facilitate water management and crop production by assessing removal of superfluous salts from the soil substratum. 相似文献
84.
The study uses the technique of factorial design for analysis of factors governing secondary dispersion of As in an auriferous Archean greenstone belt. Details of the sampling procedure and analytical techniques used for As in groundwater and soil of the Hutti–Maski schist belt are discussed in Part I of the paper in this issue. The main effects and interactions of topographic slope, drainage texture, proximity to lineament, depth of water table and soil types have been considered. The study shows that secondary dispersion of As is governed by proximity to lineament and factors that govern drainage and ground water movement. The factors retained were used to predict As values using a response surface model obtained by least square fitting using orthogonal polynomials. The goodness of fit of the model shows that the factors identified explain the secondary dispersion of As adequately. 相似文献
85.
Khem Singh S. Tiwari A. K. Jha Shankar G. Aggarwal D. S. Bisht B. P. Murty Zahid H. Khan Prabhat K. Gupta 《Natural Hazards》2013,68(2):775-789
Size distribution of PM10 mass aerosols and its ionic characteristics were studied for 2 years from January 2006 to December 2007 at central Delhi by employing an 8-stage Andersen Cascade Impactor sampler. The mass of fine (PM2.5) and coarse (PM10?2.5) mode particles were integrated from particle mass determined in different stages. Average concentrations of mass PM10 and PM2.5 were observed to be 306 ± 182 and 136 ± 84 μg m?3, respectively, which are far in excess of annual averages stipulated by the Indian National Ambient Air Quality Standards (PM10: 60 μg m?3 and PM2.5: 40 μg m?3). The highest concentrations of PM10?2.5 (coarse) and PM2.5 (fine) were observed 505 ± 44 and 368 ± 61 μg m?3, respectively, during summer (June 2006) period, whereas the lower concentrations of PM10?2.5 (35 ± 9 μg m?3) and PM2.5 (29 ± 13 μg m?3) were observed during monsoon (September 2007). In summer, because of frequent dust storms, coarse particles are more dominant than fine particles during study period. However, during winter, the PM2.5 contribution became more pronounced as compared to summer probably due to enhanced emissions from anthropogenic activities, burning of biofuels/biomass and other human activities. A high ratio (0.58) of PM2.5/PM10 was observed during winter and low (0.24) during monsoon. A strong correlation between PM10 and PM2.5 (r 2 = 0.93) was observed, indicating that variation in PM10 mass is governed by the variation in PM2.5. Major cations (NH4 +, Na+, K+, Ca2+ and Mg2+) and anions (F?, Cl?, SO4 2? and NO3 ?) were analyzed along with pH. Average concentrations of SO4 2? and NO3 ? were observed to be 12.93 ± 0.98 and 10.33 ± 1.10 μg m?3, respectively. Significant correlation between SO4 2? and NO3 ? in PM1.0 was observed indicating the major sources of secondary aerosol which may be from thermal power plants located in the southeast and incomplete combustion by vehicular exhaust. A good correlation among secondary species (NH+, NO3 ? and SO4 2?) suggests that most of NH4 + is in the form of ammonium sulfate and ammonium nitrate in the atmosphere. During winter, the concentration of Ca2+ was also higher; it may be due to entrainment of roadside dust particles, traffic activities and low temperature. The molar ratio (1.39) between Cl? and Na+ was observed to be close to that of seawater (1.16). The presence of higher Cl? during winter is due to western disturbances and probably local emission of Cl? due to fabric bleaching activity in a number of export garment factories in the proximity of the sampling site. 相似文献
86.
India's coastline is under tremendous pressure. The current processes of development are becoming a threat to the ecology and livelihoods housed on the coast. If left unchecked, there will not be much of a coast left for our future generations. GIS provides tremendous opportunities to map spatial information for better decision‐making. Government agencies generate maps, but they are localized and inaccessible, preventing an actual assessment of the damage that is already happening to our coast. The Coastal Area Mapping Project (CAMP) envisions creating a collaborative GIS platform using open source technologies. CAMP's vision is to use Free and Open Source Software (FOSS) for collaboration and cocreation and collective problem solving. CAMP foresees a vision for India's coastline where power is equalized among all constituencies (Government, corporations, media, communities, civil societies, etc.), by capturing the big picture and patterns, thus enabling the creation of strategies for stewardship of India's coastline for human wellbeing, coastal protection and sustainable coastal development. 相似文献
87.
Uma Shankar Kalachand Sain Michael Riedel 《Journal of the Geological Society of India》2012,79(2):199-209
The passive eastern Indian margin is rich in gas hydrates, as inferred from the wide-spread occurrences of bottom-simulating
reflectors (BSRs) and recovery of gas hydrate samples from various sites in the Krishna Godavari (KG) and Mahanadi (MN) basins
drilled by the Expedition 01 of the Indian National Gas Hydrate Program (NGHP). The BSRs are often interpreted to mark the
thermally controlled base of gas hydrate stability zone (BGHSZ). Most of the BSRs exhibit moderate to typically higher amplitudes
than those from other seismic reflectors. We estimate the average geothermal gradient of ∼40°C/km and heat flow varying from
23 to 62 mW/m2 in the study area utilizing the BSR’s observed on seismic sections. Further we provide the BGHSZ where the BSR is not continuous
or disturbed by local tectonics or hidden by sedimentation patterns parallel to the seafloor with a view to understand the
nature of BSR. 相似文献
88.
K. Golap N. Udaya Shankar S. Sachdev R. Dodson Ch. V. Sastry 《Journal of Astrophysics and Astronomy》1998,19(1-2):35-53
A new, meter-wave radio telescope has been built in the north-east of Mauritius, an island in the Indian Ocean, at a latitude
of -20.14‡. The Mauritius Radio Telescope (MRT) is a Fourier Synthesis T-shaped array, consisting of a 2048 m long East-West
arm and an 880 m long South arm. In the East-West arm 1024 fixed helices are arranged in 32 groups and in the South arm 16
trolleys, with four helices on each, which move on a rail are used. A 512-channel digital complex correlation receiver is
used to measure the visibility function. At least 60 days of observing are required for obtaining the visibilities up to 880
m spacing. The Fourier transform of the calibrated visibilities produces a map of the area of the sky under observation with
a synthesized beam width 4′ × 4.6′ sec(δ + 20.14‡) at 151.5 MHz.
The primary objective of the telescope is to produce a sky survey in the declination range –70‡ to –10‡ with a point source
sensitivity of about 200 mJy (3a level). This will be the southern sky equivalent of the Cambridge 6C survey. In this paper
we describe the telescope, discuss the array design and the calibration techniques used, and present a map made using the
telescope. 相似文献
89.
This paper describes a probabilistic approach in the estimation of the sediment transport along the reclaimed shoreline at the Singapore Changi Airport through a detailed analysis of the data obtained from a radio-active tracer experiment conducted on site by the Port of Singapore Authority (PSA).The probabilistic approach showed that the transport rate per unit transverse width of the beach is proportional to the effective depth of transport and the speed of the centroid of the probability function describing the dispersion of the cloud of tracers. 相似文献
90.
Uma?Shankar Babita?Sinha N.?K.?ThakurEmail author Ramesh?Khanna 《Marine Geophysical Researches》2005,26(1):29-35
Velocity analysis of multi-channel seismic (MCS) data and amplitude-versus-offset (AVO) modeling provides an efficient way
of identifying gas hydrate and free gas, and therefore the nature of the bottom-simulating reflector (BSR). Additionally,
AVO modeling also yields estimates of the hydrate concentration and free gas saturation across the BSR in terms of velocity
distribution. In the present study, we apply directivity correction in order to accentuate the AVO behavior. Modeling for
AVO pattern of the observed BSR over the Kerala–Konkan Offshore Basin may provide the probable velocity distribution across
the BSR and thereby infer whether hydrate or hydrate/free gas model governs the AVO observations. Initial results indicate
the possible presence of free gas underlying the gas hydrates-saturated sediments in this region. 相似文献