Solar UV variability: Effects on stratospheric ozone,trace constituents and thermal structure     

Murali Natarajan  Linwood B. Callis  John E. Nealy 《Pure and Applied Geophysics》1980,119(4):750-779

The effect of long-term (11-year solar cycle) solar UV variability on stratospheric chemical and thermal structure has been studied using a time-dependent one-dimensional model. Previous studies have suggested substantial variations in local and total ozone, and in stratospheric thermal structure from solar minimum to solar maximum. It is shown here that significant variations also occur in some of the trace constituents. Members of the HO _x family and N₂O exhibit the largest variations, and these changes, if detected, may provide additional means of verifying the presence of solar UV variability and its effects. Some of the species show large phase differences with the assumed solar flux variation. The role of chemical and transport time constants on the time variations of the trace species is examined. Comparisons with reported ozone and temperature data show reasonable agreement for the period 1960 to 1972.  相似文献   

Vegetation pattern of Istanbul from the Landsat data and the relationship with meteorological parameters     

Zafer Aslan  Krishnaier Natarajan  Mehmet Tankut 《Annales Geophysicae》1994,12(6):574-584

This paper discusses the preliminary results of a study on the vegetation pattern and its relationship with meteorological parameters in and around Istanbul. The study covers an area of over 6800 km² consisting of urban and suburban centers, and uses the visible and near-infrared bands of Landsat. The spatial variation of the Normalized Difference Vegetation Index (NDVI) and meteorological parameters such as sensible heat flux, momentum flux, relative humidity, moist static energy, rainfall rate and temperature have been investigated based on observations in ten stations in the European (Thracian) and Anatolian parts of Istanbul. NDVI values have been evaluated from the Landsat data for a single day, viz. 24 October 1986, using ERDAS in ten different classes. The simultaneous spatial variations of sensible heat and momentum fluxes have been computed from the wind and temperature profiles using the Monin-Obukhov similarity theory. The static energy variations are based on the surface meteorological observations. There is very good correlation between NDVI and rainfall rate. Good correlation also exists between: NDVI and relative humidity; NDVI, sensible heat flux and relative humidity; NDVI, momentum flux and emissivity; and NDVI, sensible heat flux and emissivity. The study suggests that the momentum flux has only marginal impact on NDVI. Due to rapid urbanization, the coastal belt is characterized by reduced NDVI compared to the interior areas, suggesting that thermodynamic discontinuities considerably influence the vegetation pattern. This study is useful for the investigation of small-scale circulation models, especially in urban and suburban areas where differential heating leads to the formation of heat islands. In the long run, such studies on a global scale are vital to gain accurate, timely information on the distribution of vegetation on the earth’s surface. This may lead to an understanding of how changes in land cover affect phenomena as diverse as the atmospheric CO² concentrations, the hydrological cycle and the energy balance at the surface-atmosphere interface.  相似文献   

Warped discs and the directional stability of jets in active galactic nuclei     

Priyamvada Natarajan  Philip J. Armitage 《Monthly notices of the Royal Astronomical Society》1999,309(4):961-968

The radial distribution of globular clusters in galaxies is always less peaked to the centre than that of the halo stars. Extending previous work to a sample of Hubble Space Telescope globular cluster systems in ellipticals, we evaluate the number of clusters potentially lost to the galactic centre as the integrals of the difference between the observed globular cluster system distribution and the underlying halo light profile. In the sample of galaxies examined it is found that the initial populations of globular clusters may have been ∼30 per cent to 50 per cent richer than now. If these 'missing' globular clusters have decayed and have been partly destroyed in the very central galactic zones, they have carried there a significant quantity of mass that, plausibly, contributed to the formation and feeding of a massive object therein. It is relevant to note that the observed correlation between the core radius of the globular cluster system and the parent galaxy luminosity can be interpreted as a result of evolution.  相似文献   

Pre-earthquake Atmospheric and Ionospheric Anomalies before Taiwan Earthquakes (M 6.1 and M 6.4) on February (4th and 6th), 2018     

Prasanna Simha  C.  Natarajan  Venkatanathan  Rao  Katlamudi Madhusudhana 《Geomagnetism and Aeronomy》2020,60(5):644-660

Geomagnetism and Aeronomy - Satellite measurements are becoming popular among the scientific community to identify earthquake precursors since its spatial coverage is more and round the clock...  相似文献   

Quartz surface microtextural studies of Cauvery River sediments,Tamil Nadu,India     

Natarajan Gobala krishnan  Raghavendramurthy Nagendra  Lakshmanan Elango 《Arabian Journal of Geosciences》2015,8(12):10665-10673

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Is there an upper limit to black hole masses?     

Priyamvada Natarajan  Ezequiel Treister 《Monthly notices of the Royal Astronomical Society》2009,393(3):838-845

We make a case for the existence for ultra-massive black holes (UMBHs) in the Universe, but argue that there exists a likely upper limit to black hole (BH) masses of the order of   M ∼ 10¹⁰ M_⊙  . We show that there are three strong lines of argument that predicate the existence of UMBHs: (i) expected as a natural extension of the observed BH mass bulge luminosity relation, when extrapolated to the bulge luminosities of bright central galaxies in clusters; (ii) new predictions for the mass function of seed BHs at high redshifts predict that growth via accretion or merger-induced accretion inevitably leads to the existence of rare UMBHs at late times; (iii) the local mass function of BHs computed from the observed X-ray luminosity functions of active galactic nuclei predict the existence of a high-mass tail in the BH mass function at   z = 0  . Consistency between the optical and X-ray census of the local BH mass function requires an upper limit to BH masses. This consistent picture also predicts that the slope of the   M _bh–σ  relation will evolve with redshift at the high-mass end. Models of self-regulation that explain the co-evolution of the stellar component and nuclear BHs naturally provide such an upper limit. The combination of multiwavelength constraints predicts the existence of UMBHs and simultaneously provides an upper limit to their masses. The typical hosts for these local UMBHs are likely the bright, central cluster galaxies in the nearby Universe.  相似文献   

Angular momentum and clustering properties of early dark matter haloes     

Andrew J. Davis  Priyamvada Natarajan 《Monthly notices of the Royal Astronomical Society》2009,393(4):1498-1502

In this paper, we study the angular momentum properties of simulated dark matter haloes at high redshifts that likely host the first stars in the Universe. Calculating the spin distributions of these  10⁶– 10⁷ M_⊙  haloes in redshift slices from   z = 15  to 6, we find that they are well fit by a lognormal distribution as is found for lower redshift and more massive haloes in earlier work. We find that both the mean value of the spin and dispersion are largely unchanged with redshift for all haloes. Our key result is that subsamples of low- and high-spin, 10⁶ and  10⁷ M_⊙  , haloes show difference in clustering strength. In both mass bins, higher spin haloes are more strongly clustered in concordance with a tidal torquing picture for the growth of angular momentum in dark matter haloes in the cold dark matter paradigm.  相似文献   

Multilinear Regression Analysis for Seismic Response and Engineering Properties of Liquefiable Coromandel Coastal Soil Deposits   总被引：1，自引：0，他引：1  

S. Senthamilkumar  C. Natarajan  K. Muthukumaran 《Geotechnical and Geological Engineering》2009,27(3):439-453

This paper investigates the seismic characteristics and geotechnical properties with respect to the liquefaction potential of the deposits in the Coromandel coastal line of Nagapattinam town, Tamilnadu, India. A series of field tests were conducted using standard penetration test, cone penetration test and plate load test. Laboratory tests were conducted on the collected samples. From the results, a microzonation map was developed for the liquefaction potential and settlements. Some multilinear regression models between permeability, fines content, relative density, coefficient of curvature, coefficient of uniformity, mean particle size, factor of safety, settlement, standard penetration test values and cone penetration test values were developed. The shear wave velocity and shear modulus were calculated from the field penetration tests and correlations between the normalized values of peak ground accelerations, velocities and displacements, which were obtained from the equivalent linear ground motion analysis using SHAKE software, with other parameters of soil. From the results, it was found that at some of the areas are vulnerable to high amplification of waves even for small earthquake.  相似文献   

Land use study in Mewat area,Haryana, using remote sensing techniques     

S. Natarajan  N. Y. Gajbe  M. L. Manchanda 《Journal of the Indian Society of Remote Sensing》1986,14(1):17-24

A soil and land use survey of Mewat area, Haryana, was carried out using the aerial photographs of 1:50,000. Four major physiographic units namely hills, piedmont plain, intermontante basin and Yamuna alluvial plain were recognised. The land use was studied in relation to the physiographic units. The legend adopted for land use classification has physiography at first level, utility at second level and management and identification at third and fourth levels respectively. Of the total area of 161,103 ha surveyed, 131,637 ha (81.72%) are cultivated. Of this 75,967 ha (47.16%) irrigated and 55,670 ha (34.56%) is unirrigated. Under uncultivated area, barren lands cover 14,224 ha (8.82%), forests occupy 3,463 ha (5.25%), settlements cover 3,300 (2.05%), water bodies occupy 1,312 ha (0.81%) and roads, railway lines, canals and drains constitute 2,167 ha (1.55%).  相似文献   

Numerical investigation on the dynamics of a vertical wall defenced by an offshore breakwater   总被引：1，自引：0，他引：1  

M.G. Muni Reddy  S.A. Sannasiraj  R. Natarajan   《Ocean Engineering》2007,34(5-6):790-798

The numerical and experimental investigations on the performance of an offshore-submerged breakwater in reducing the wave forces and wave run-up on vertical wall are presented. A two-dimensional finite-element model is employed to study the hydrodynamic performance of the submerged breakwater under the action of regular and random waves. The numerical prediction has been supported with experimental measurements. The wave forces and wave run-up on the vertical wall were measured for different breakwater configurations. The applicability of linear theoretical model in the prediction of wave forces on the wall by a submerged breakwater has been discussed.  相似文献