Variations in vapor pressure and standardized precipitation evapotranspiration index since AD 1861 over the western Himalaya in India: inference from tree ring-width records     

Somaru Ram  H. N. Singh  Ramesh Kumar Yadav  Hamza Varikoden  S. S. Nandargi  Manoj K. Srivastava 《Theoretical and Applied Climatology》2020,140(1):157-166

A regional tree ring-width index chronology prepared from various tree core samples of the western Himalaya has been analyzed in relation to climate fluctuations. The correlation analysis of tree ring chronology shows significant positive correlations with regional rainfall and standardized precipitation evapotranspiration index (SPEI) and negative correlations with temperature and vapor pressure (VP) during the spring season. The correlation coefficients (CCs) of tree ring-width index chronology with rainfall, temperature, SPEI, and VP during 1901–1990 are 0.50, −0.49, 0.65, and −0.51, respectively. All CCs are significant at 0.1% level. The highly significant CCs between tree ring-width index chronology and SPEI indicate that tree growth over the western Himalaya is more sensitive to soil moisture availability than rainfall, whereas the rising VP is found to have a significant moisture stress condition to tree growth by accelerating the evapotranspiration, which is not conducive for the development of tree growth in the region. So, based on the strong association between tree ring-width index chronology and SPEI; the reconstructions of SPEI and VP are developed back to AD 1861, that show the long period of dryness during 1936–1963.  相似文献   

Spatially explicit surface energy budget and partitioning with remote sensing and flux measurements in a boreal region of Interior Alaska     

Shengli Huang  Devendra Dahal  Ramesh Singh  Heping Liu  Claudia Young  Shuguang Liu 《Theoretical and Applied Climatology》2013,113(3-4):549-560

Extrapolating energy fluxes between the ground surface and the atmospheric boundary layer from point-based measurements to spatially explicit landscape estimation is critical to understand and quantify the energy balance components and exchanges in the hydrosphere, atmosphere, and biosphere. This information is difficult to quantify and are often lacking. Using a Landsat image (acquired on 5 August 2004), the flux measurements from three eddy covariance flux towers (a 1987 burn, a 1999 burn, and an unburned control site) and a customized satellite-based surface energy balance model of Mapping Evapotranspiration at High Resolution with Internalized Calibration (METRIC), we estimated net radiation, sensible heat flux (H), latent heat flux (LE), and soil heat flux (G) for the boreal Yukon River Basin of Interior Alaska. The model requires user selection of two extreme conditions present within the image area to calibrate and anchor the sensible flux output. One is the “hot” condition which refers to a bare soil condition with specified residual evaporation rates. Another one is the “cold” condition which refers to a fully transpiring vegetation such as full-cover agricultural crops. We selected one bare field as the “hot” condition while we explored three different scenarios for the “cold” pixel because of the absence of larger expanses of agricultural fields within the image area. For this application over boreal forest, selecting agricultural fields whose evapotranspiration was assumed to be 1.05 times the alfalfa-based reference evapotranspiration as the “cold” pixel could result in large errors. Selecting an unburned flux tower site as the “cold” pixel could achieve acceptable results, but uncertainties remain about the energy balance closure of the flux towers. We found that METRIC performs reasonably well in partitioning energy fluxes in a boreal landscape.  相似文献   

A telescope made with cylinders – I. Some analytical results     

Ramesh Balasubramanyam 《Monthly notices of the Royal Astronomical Society》2004,354(4):1189-1193

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Exact relativistic model for a superdense star     

P. C. Vaidya  Ramesh Tikekar 《Journal of Astrophysics and Astronomy》1982,3(3):325-334

Assuming that the physical 3-spacet = const in a superdense star is spheroidal, a static spherically symmetric model based on an exact solution of Einstein’s equations is given which will permit densities of the order of 2 × 10¹⁴ gm cm^-3, radii of the order of a few kilometers and masses up to about four times the solar mass.  相似文献   

Some implications of escape of supermassive black holes from galactic nuclei due to plasmoid ejection     

Ramesh Chander Kapoor 《Astrophysics and Space Science》1983,95(2):425-429

Shklovsky (1982) has hypothesized escape of accreting supermassive black holes from galactic nuclei as a consequence of asymmetric ejection of plasma clouds from their accretion disks and their subsequent defunction for explaining evolutionary effects in quasars. It has been argued here that such an interpretation must accomodate the possibility of substantial capture of stars and gas by the black hole on its way out-which can prolong the life of the quasar-unless the mass of the black hole is less than ～10⁷ M _⊙ and a large enough initial recoil velocity is achieved.  相似文献   

The 1024 channel digital correlator receiver of the Gauribidanur radioheliograph     

R. Ramesh  M. S. Sundara Rajan  Ch. V. Sastry 《Experimental Astronomy》2006,21(1):31-40

A low frequency (40–150 MHz) radioheliograph for observations of the solar corona is in operation for the last few years at the Gauribidanur radio observatory, about 100 km north of Bangalore. The array has 32 antenna groups and a 1-bit digital correlator system consisting of 1024 channels is used as the back-end receiver. This paper describes the latter and results of the associated system tests.  相似文献   

Modeling and Mapping High Water Table for a Coastal Region in Florida using Lidar DEM Data     

Caiyun Zhang  Hongbo Su  Tiantian Li  Weibo Liu  Diana Mitsova  Sudhagar Nagarajan  Ramesh Teegavarapu  Zhixiao Xie  Fred Bloetscher  Yan Yong 《Ground water》2021,59(2):190-198

Predicting and mapping high water table elevation in coastal landscapes is critical for both science application projects like inundation risk analysis and engineering projects like pond design and maintenance. Previous studies of water table mapping focused on the application of geostatistical methods, which cannot predict values beyond an observation spatial domain or generate an ideal pattern for regions with sparse measurements. In this study, we evaluated the multiple linear regression (MLR) and support vector machine (SVM) techniques for high water table prediction and mapping using fine spatial resolution lidar-derived Digital Elevation Model (DEM) data, and designed an application protocol of these two techniques for high water table mapping in a coastal landscape where groundwater, tide, and surface water are related. Testing results showed that SVM largely improved the high water table prediction with a mean absolute error (MAE) of 1.22 feet and root mean square error (RMSE) of 2.22 feet compared to the application of the ordinary Kriging method which could not generate a reasonable water table. MLR was also promising with a MAE of around 2 feet and RMSE of around 3 feet. The study suggests that both MLR and SVM are valuable alternatives to estimate high water table elevation in Florida. Fine resolution lidar DEMs are beneficial for high water table prediction and mapping.  相似文献   

Multivariate water quality assessment from the Tamiraparani river basin,Southern India     

P. Kumarasamy  R. Arthur James  Hans-Uwe Dahms  Chan-Woo Byeon  R. Ramesh 《Environmental Earth Sciences》2014,71(5):2441-2451

The hydrochemistry of a perennial river has been investigated with multivariate cluster analysis (CA) and principal component analysis/factor analysis (PCA/FA). The aim was to investigate parameters responsible for spatial and temporal variations of river water quality. Water quality was monitored along the river basin at 20 different sites over a period of 1 year from July, 2008 to June, 2009. Multivariate statistics revealed that Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃ ^?, Cl^?, H₄SiO₄, SO₄ ^2?, NO₂ ^?, and PO₄ ^3? were influenced by seasonal and spatial variations and that water quality was in the first place determined more by natural weathering processes than by anthropogenic activities. We could prove by (a) Box and Whisker plot, (b) matrix scatter score mean plot, (c) ternary plot, and (d) Gibbs plot that the chemistry of river water is controlled by lithogenic weathering processes. The higher concentration of dissolved silica during summer and the pre-monsoon season is explained by natural and tropical climatic conditions of the environment.  相似文献   

Revisit to graphite-tungsten deposits of East Godavari district,Andhra Pradesh     

Ramesh M. Umathay  Anil M. Pophare 《Journal of the Geological Society of India》2014,84(4):417-430

The graphite-tungsten deposits under consideration in this study are located in the Burugubanda, Pydiputta, Tapasikonda, Marripalem and Madyaratigudem areas of the East Godavari district of Andhra Pradesh, India. These deposits were formed due to wide spread tectonothermal events associated with the evolution of Eastern Ghats Mobile Belt (EGMB). The graphite deposits of East Godavari district are epigenetic, rhombohedral fluid deposited type and are one of the four deposits of such type reported so far from Srilanka, Spain and England. The graphite deposits were formed due to granodioritic intrusion into the Narsipatnam shear zone, which caused migmatisation of khondalites along with mobilisation and concentration of graphite, as veins and lenses, into the graphite gneisses. The graphite gneisses were subsequently intruded by quartz rich pegmatites that were laden with tungsten mineralisation. The tungsten mineralisation occurs as thin bands, lenses, stringers and vein lets within the quartz matrix and also dispersed in the graphite gneisses. Inclusions of tungsten in graphite indicate that tungsten mineralisation succeeded graphite mineralisation. However, the low P-T phenomenon of tungsten (wolframite-ferberite) mineralisation resulted in low tenor of tungsten ore deposits (WO₃: 0.10%). Rare earth elements (REE) are associated with tungsten mineralisation in these areas. During the present study, these graphite-tungsten deposits have been re-examined, in the backdrop of shelving graphite-tungsten projects in these areas. The feed for mineral beneficiation tests was decided on the basis of dispersion of tungsten in quartz and graphite rich fractions of the ore zone. The feed (ROM material) on beneficiation gave recovery of +75% graphite concentrate, tungsten concentrate of consistent chemical grade, besides recovery of sizeable REE concentrate. It also rendered use of unutilised graphite tailing dumps at beneficiation plants, thereby effecting conservation. Thus, the association of tungsten and REE with the entire graphite deposits along with their value addition during beneficiation, as by-product, revived opportunities to restart graphite mining in the Burugubanda, Pydiputta and Tapasikonda areas in particular and East Godavari district, in general, as an economically viable venture. This will initiate opening of graphite mines in other districts of Andhra Pradesh and energise economics of working graphite mines within EGMB, in the states of Jharkhand, Odisha and Tamil Nadu.  相似文献   

MARSpline model for lead seven-day maximum and minimum air temperature prediction in Chennai,India     

K Ramesh  R Anitha 《Journal of Earth System Science》2014,123(4):665-672

In this study, a Multivariate Adaptive Regression Spline (MARS) based lead seven days minimum and maximum surface air temperature prediction system is modelled for station Chennai, India. To emphasize the effectiveness of the proposed system, comparison is made with the models created using statistical learning technique Support Vector Machine Regression (SVMr). The analysis highlights that prediction accuracy of MARS models for minimum temperature forecast are promising for short term forecast (lead days 1 to 3) with mean absolute error (MAE) less than 1 °C and the prediction efficiency and skill degrades in medium term forecast (lead days 4 to 7) with slightly above 1 °C. The MAE of maximum temperature is little higher than minimum temperature forecast varying from 0.87 °C for day-one to 1.27 °C for lag day-seven with MARS approach. The statistical error analysis emphasizes that MARS models perform well with an average 0.2 °C of reduction in MAE over SVMr models for all ahead seven days and provide significant guidance for the prediction of temperature event. The study also suggests that the correlation between the atmospheric parameters used as predictors and the temperature event decreases as the lag increases with both approaches.  相似文献