Role of orography in modulating space–time scales of convection over South Asia     

Arindam Chakraborty  Ravi S. Nanjundiah 《Theoretical and Applied Climatology》2014,116(3-4):549-564

Propagation of convective systems in the meridional direction during boreal summer is responsible for active and break phases of monsoon over south Asia. This region is unique in the world in its characteristics of monsoon variability and is in close proximity of mountains like the Himalayas. Here, using an atmospheric general circulation model, we try to understand the role of orography in determining spatial and temporal scales of these convective systems. Absence of orography (noGlOrog) decreased the simulated seasonal mean precipitation over India by 23 % due to delay in onset by about a month vis-a-vis the full-mountain case. In noGlOrog, poleward propagations were absent during the delayed period prior to onset. Post-onset, both simulations had similar patterns of poleward propagations. The spatial and temporal scales of propagating clouds bands were determined using wavelet analysis. These scales were found to be different in full-mountain and no-mountain experiments in June–July. However, after the onset of monsoon in noGlOrog, these scales become similar to that with orography. Simulations with two different sets of convection schemes confirmed this result. Further analysis shows that the absence (presence) of meridional propagations during early (late) phase of summer monsoon in noGlOrog was associated with weaker (stronger) vertical shear of zonal wind over south Asia. Our study shows that orography plays a major role in determining the time of onset over the Indian region. However, after onset, basic characteristics of propagating convective systems and therefore the monthly precipitation over India, are less sensitive to the presence of orography and are modulated by moist convective processes.  相似文献   

Dissolved Boron in the Tapi,Narmada and the Mandovi Estuaries,the Western Coast of India: Evidence for Conservative Behavior     

Satinder Pal Singh  Sunil Kumar Singh  Ravi Bhushan 《Estuaries and Coasts》2014,37(4):1017-1027

The concentrations of dissolved boron have been measured during different seasons in three estuaries, the Tapi, Narmada and the Mandovi situated on the western coast of India, to investigate its geochemical behavior and inputs from the localized anthropogenic pressures of industrial effluents and sewage discharge. The measured boron concentrations in these estuaries (except the Tapi during non-monsoon) at salinity ≤0.1 fall in a narrow range?～?2–4 μmol/kg (average B?～?2.4?±?0.8 μmol/kg) within the reported wide range?～?0.1–18.6 μmol/kg for global rivers. The much higher estimate of boron concentration in the Tapi River during non-monsoon is attributed to its possible additional supply from the sewage and/or industrial effluents discharged along the river course. During monsoon, the rains seem to be a significant source of dissolved boron to all the three rivers. The distribution of dissolved boron in each estuary exhibits a conservative behavior during the seasons sampled suggestive of no measurable addition or removal of boron in the estuarine region. The orders of magnitude differences in boron concentration between the river waters and seawater, and the conservative behavior of dissolved boron indicate that its major contributor to the estuaries sampled is seawater.  相似文献   

Geochemical characterization and heavy metal contamination of groundwater in Satluj River Basin   总被引：1，自引：0，他引：1  

Chander Kumar Singh  Kumari Rina  Ravi Prakash Singh  Saumitra Mukherjee 《Environmental Earth Sciences》2014,71(1):201-216

Groundwater, a renewable and finite natural resource, vital for man’s life, social and economic development and a valuable component of the ecosystem, is vulnerable to natural and human impacts. The aim of present study is to evaluate hydrogeochemical parameters and heavy metals in groundwater and to study their spatial distribution in the Rupnagar District of Punjab. The spatial distribution of physico-chemical parameters were studied using Arc GIS 9.2. It was observed that the concentration of parameters, such as NO₃, Cd, Cr, Mn and Pb was above permissible limit (World Health Organization, WHO) in southern part of the study area. The heavy metal pollution index (HPI) was calculated for all sampling locations and it was found much above the critical limit of pollution. Geochemical reaction models of selected water groups were constructed using Phreeqc. Geochemical modeling suggests that sodium has source other than halite-albite and calcium has alternate source other than gypsum-carbonate or silicates. It also suggests that evaporites, ion exchange, dissolution along with anthropogenic activities are controlling the hydro-geochemistry of groundwater in the region. Various indices, such as heavy metal pollution index, permeability index, sodium adsorption ratio, were studied to verify suitability of groundwater for drinking and irrigation.  相似文献   

Hydrogeological processes controlling the release of arsenic in parts of 24 Parganas district,West Bengal     

Neha Singh  Ravi Prakash Singh  Saumitra Mukherjee  Kyle McDonald  K. J. Reddy 《Environmental Earth Sciences》2014,72(1):111-118

A study was conducted to understand the hydrogeological processes dominating in the North 24 Parganas and South 24 Parganas based on representative 39 groundwater samples collected from selected area. The abundance of major ions was in the order of Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ > Fe²⁺ for cations and HCO₃ ^? > PO₄ ^3? > Cl^? > SO₄ ^2? > NO₃ ^? for anions. Piper trilinear diagram was plotted to understand the hydrochemical facies. Most of the samples are of Ca-HCO₃ type. Based on conventional graphical plots for (Ca + Mg) vs. (SO₄ + HCO₃) and (Na + K) vs. Cl, it is interpreted that silicate weathering and ion exchange are the dominant processes within the study area. Previous studies have reported quartz, feldspar, illite, and chlorite clay minerals as the major mineral components obtained by the XRD analysis of sediments. Mineralogical investigations by SEM and EDX of aquifer materials have shown the occurrence of arsenic as coating on mineral grains in the silty clay as well as in the sandy layers. Excessive withdrawal of groundwater for irrigation and drinking purposes is responsible for fluctuation of the water table in the West Bengal. Aeration beneath the ground surface caused by fluctuation of the water table may lead to the formation of carbonic acid. Carbonic acid is responsible for the weathering of silicate minerals, and due to the formation of clay as a product of weathering, ion exchange also dominates in the area. These hydrogeological processes may be responsible for the release of arsenic into the groundwater of the study area, which is a part of North 24 Parganas and South 24 Parganas.  相似文献   

Estimation of sedimentary thickness in the Godavari basin     

K. Sushini  G. Srijayanthi  P. Solomon Raju  M. Ravi Kumar 《Natural Hazards》2014,71(3):1847-1860

A major portion of the southern part of the Indian subcontinent is classified as a stable continental region. However, a few segments in this region are punctuated by rifts and shear zones that are seismically active. The Godavari rift that sutures the eastern Dharwar and the Bastar cratons is one such region, prone to seismic hazard. Estimation of the sedimentary thickness in these seismically active regions assumes importance since locales of thick and soft sediments are vulnerable to destruction due to surface waves generated by earthquakes. In the present study, data from five broadband seismological stations are utilized to estimate the average sedimentary thickness of the Godavari region using the difference in travel times of the direct S and converted Sp phases from local earthquakes. The thickness of sediments varies between 0.32 and 4.32 km. Also, the site-specific response in terms of the fundamental resonance frequency and the corresponding amplifications are estimated using the well-established Nakamura technique. The predominant frequencies are in the range of 1.3–4.61 Hz, and the amplifications are higher (>1.5) for the stations inside the Godavari basin. Both the thickness and amplification values clearly indicate that the sediments tend to get thicker toward the center of the basin, in good agreement with the geological distribution of the sedimentary units.  相似文献   

Voids in a ΛCDM universe     

Jörg M. Colberg  Ravi K. Sheth  Antonaldo Diaferio  Liang Gao  Naoki Yoshida 《Monthly notices of the Royal Astronomical Society》2005,360(1):216-226

We study the formation and evolution of voids in the dark matter distribution using various simulations of the popular Λ cold dark matter cosmogony. We identify voids by requiring them to be regions of space with a mean overdensity of −0.8 or less – roughly the equivalent of using a spherical overdensity group finder for haloes. Each of the simulations contains thousands of voids. The distribution of void sizes in the different simulations shows good agreement when differences in particle and grid resolution are accounted for. Voids very clearly correspond to minima in the smoothed initial density field. Apart from a very weak dependence on the mass resolution, the rescaled mass profiles of voids in the different simulations agree remarkably well. We find a universal void mass profile of the form  ρ(< r )/ρ( r _eff) ∝ exp[( r / r _eff)^α]  , where r _eff is the effective radius of a void and  α∼ 2  . The mass function of haloes in voids is steeper than that of haloes that populate denser regions. In addition, the abundances of void haloes seem to evolve somewhat more strongly between redshifts ∼1 and 0 than the global abundances of haloes.  相似文献   

Investigation of Soil Suction Characteristics Induced by the Degradation of Organic Matter     

Dubey  Anant Aishwarya  Borthakur  Annesh  Ravi  K. 《Geotechnical and Geological Engineering》2022,40(4):2371-2378

Geotechnical and Geological Engineering - Total soil suction is considered to be the accumulative influence of matric and osmotic suction, assuming that the soil is biologically inert. However,...  相似文献   

Modulations in the radio light curve of the Type IIb supernova 2001ig: evidence for a Wolf–Rayet binary progenitor?     

Stuart D. Ryder  Elaine M. Sadler  Ravi Subrahmanyan  Kurt W. Weiler  Nino Panagia  Christopher Stockdale 《Monthly notices of the Royal Astronomical Society》2004,349(3):1093-1100

  相似文献   

Climate change and crop yields in the Indian Cardamom Hills, 1978–2007 CE     

Muthusamy Murugan  Paddu Krishnappa Shetty  Raju Ravi  Aavudai Anandhi  Arulappan Joseph Rajkumar 《Climatic change》2012,110(3-4):737-753

In this study we analyzed climate and crop yields data from Indian cardamom hills for the period 1978–2007 to investigate whether there were significant changes in weather elements, and if such changes have had significant impact on the production of spices and plantation crops. Spatial and temporal variations in air temperatures (maximum and minimum), rainfall and relative humidity are evident across stations. The mean air temperature increased significantly during the last 30?years; the greatest increase and the largest significant upward trend was observed in the daily temperature. The highest increase in minimum temperature was registered for June (0.37°C/18?years) at the Myladumpara station. December and January showed greater warming across the stations. Rainfall during the main monsoon months (June–September) showed a downward trend. Relative humidity showed increasing and decreasing trends, respectively, at the cardamom and tea growing tracts. The warming trend coupled with frequent wet and dry spells during the summer is likely to have a favorable effect on insect pests and disease causing organisms thereby pesticide consumption can go up both during excess rainfall and drought years. The incidence of many minor pest insects and disease pathogens has increased in the recent years of our study along with warming. Significant and slight increases in the yield of small cardamom (Elettaria cardamomum M.) and coffee (Coffea arabica), respectively, were noticed in the recent years.; however the improvement of yield in tea (Thea sinensis) and black pepper (Piper nigrum L.) has not been seen in our analysis.  相似文献   

The non-linear probability distribution function in models with local primordial non-Gaussianity     

Tsz Yan Lam  Ravi K. Sheth 《Monthly notices of the Royal Astronomical Society》2009,395(3):1743-1748

We use the spherical evolution approximation to investigate non-linear evolution from the non-Gaussian initial conditions characteristic of the local f _nl model. We provide an analytic formula for the non-linearly evolved probability distribution function (PDF) of the dark matter which shows that the underdense tail of the non-linear PDF in the f _nl model should differ significantly from that for Gaussian initial conditions. Measurements of the underdense tail in numerical simulations may be affected by discreteness effects, and we use a Poisson counting model to describe this effect. Once this has been accounted, our model is in good quantitative agreement with the simulations. In principle, our calculation is an important first step in programs which seek to reconstruct the shape of the initial PDF from observations of large-scale structures in the Lyα forest and the galaxy distribution at later times.  相似文献