Diurnal variation of precipitation over the Carolina Sandhills region     

A. Wootten  S. Raman  A. Sims 《Journal of Earth System Science》2010,119(5):579-596

The Carolina Sandhills are known to have an area of maximum precipitation on its western boundary during the summer mainly due to differences in soil types. Statistical analysis was performed on summer precipitation data from automated weather stations in the Carolinas, along the Sandhills for the years 2001 to 2006. Statistically significant difference was observed between the day and night precipitation amounts. A case study also revealed the diurnal pattern of convective precipitation.  相似文献   

Solar X-Ray Spectral Irradiance Variability     

K. B. Ramesh  K. Sundara Raman 《Solar physics》2006,234(2):393-408

Solar spectral irradiance at X-ray wavelengths show large variations over a period of solar cycle. We use X-ray irradiance data in three narrow spectral regimes deduced from Yohkoh SXT measurements to study coronal irradiance and their possible association with the activity in the lower atmosphere. Time variation of the X-ray irradiance is important in understanding the emergence of magnetic flux and the effects of such variation on the upper atmosphere of the Earth. We note that about 66% of the total (2 – 30 Å) X-ray irradiance arise from 10 to 20 Å spectral range, while 2 – 10 Å contribute only about 3% of the total. The time variation in 2 – 10 and 10 – 20 Å ranges follow each other closely. Further they follow closely the solar indices such as sunspot, F _10.7, and plage indices, although similarity in the variation of 10 – 20 Å is quite apparent. However, the variation in the other spectral band (20 – 30 Å) differ to a large extent except for the solar cycle dependent variation. We infer that in addition to the active regions, the remnants of active regions contribute considerably to the emission in this spectral range.  相似文献   

Conference on Sustainable Mining and the United Nations Framework Classification (UNFC): Challenges and Opportunities in India     

R. H. Sawkar  C. V. Raman 《Journal of the Geological Society of India》2013,82(6):725-726

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On the reliability of C iv λ1549 as an abundance indicator for high-redshift star-forming galaxies     

Paul A. Crowther  Raman K. Prinja  Max Pettini  Charles C. Steidel 《Monthly notices of the Royal Astronomical Society》2006,368(2):895-902

We reconsider the use of the equivalent width of C  iv  λ1549, EW(C  iv ), as an indicator of the oxygen abundance in star-forming galaxies, as proposed by Heckman et al. for nearby starbursts. We refine the local calibration of EW(C  iv ) versus log (O/H) by using a restricted wavelength window which minimizes blending with interstellar absorption lines. When applied to the stellar component only of the complex C  iv  λ1549 features in two high-redshift galaxies with good quality spectra,  MS 1512−cB58 ( z = 2.7268)  and  Q1307−BM1163 ( z = 1.4105)  , the local calibration gives values of the oxygen abundance which are in good agreement with other metallicity determinations based on nebular emission and interstellar absorption lines. Our main conclusion is that for this method to give reliable results at high redshifts, it should only be used on data of sufficiently high spectral resolution  ( R ≳ 1000)  for stellar and interstellar C  iv components to be clearly separated. Oxygen abundances will be systematically overestimated if the local calibration is applied to spectra of high-redshift galaxies obtained with the low resolving powers  ( R ≃ 200–300)  of many current wide-field surveys. It will also be necessary to understand better the causes of the scatter in the local relation, before we can be confident of inferences from it at high z .  相似文献   

Preface     

G.V. Rao  S. Raman  M.P. Singh 《Pure and Applied Geophysics》2003,160(1-2):1-2

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Monsoon rainfall simulations with the Kuo and Betts-Miller schemes     

K. Alapaty  S. Raman  R. V. Madala  U. C. Mohanty 《Meteorology and Atmospheric Physics》1994,53(1-2):33-49

Summary Two numerical experiments are performed using a nested grid regional model to study the performance of the Kuo and the Betts-Miller cumulus parameterization schemes in simulating the rainfall during an active monsoon period. Results indicate that the monsoon circulation features, such as the Somali jet and monsoon depression are better simulated with the Kuo scheme. With the Kuo scheme, predicted intensity and associated rainfall of the monsoon depression are in good agreement with the observations. Uncertainty in the adjustment parameters in the Betts-Miller scheme appears to have lead to the poor prediction of rainfall. Also, the Betts-Miller scheme showed considerable sensitivity to the convergence in the lower troposphere in the initial conditions over the Arabian Sea, leading to a prediction of a spurious intense tropical cyclone. This cyclone replaced the normal heat-low over the desert region. Rainfall distribution and its maximum along the west coast of India were predicted better with the Kuo scheme. Area-averaged convective heating rates indicated that the cumulus convection is deeper and more intense with the Kuo scheme. Also, area averaged evaporation rates far exceeded the rainfall rates with the Betts-Miller scheme while with the Kuo scheme these rates are in balance after the spinup period. Forecast erros in the zonally averaged specific humidities indicate that the model atmosphere is more humid with the Betts-Miller scheme.With 14 Figures  相似文献   

Simulation of monsoon boundary-layer processes using a regional scale nested grid model     

Kiran Alapaty  Sethu Raman  R. V. Madala 《Boundary-Layer Meteorology》1994,67(4):407-426

A nested grid regional model with a high vertical resolution in the atmospheric boundary layer is used to simulate various atmospheric processes during an active monsoon period. A turbulence kinetic energy closure scheme is used to predict the boundary-layer structure. Model predictions indicate different structures of the boundary layer over land and oceans, as observed. Significant diurnal variation in boundary-layer structure and associated processes is predicted over land and negligible variations over oceans. The Somali jet over the Arabian Sea is well predicted. Location of the predicted monsoon depression and the associated rainfall are in good agreement with the observations. Also, predicted rainfall and its spatial distribution along the west coast of India are in good agreement with the observations.  相似文献   

Variation of turbulence in the marine boundary layer over the Arabian Sea during indian southwest monsoon (MONEX 79)     

Teddy Holt  Sethu Raman 《Boundary-Layer Meteorology》1986,37(1-2):71-87

Analysis of high frequency (20 Hz) turbulence data collected from low level flights by the National Center for Atmospheric Research (NCAR) Electra aircraft over the central Arabian Sea on 20 and 24 June, 1979 as part of MONEX 79 indicates the influence of the Somali Jet on boundary-layer turbulence. Different stages of monsoon development were evident on the two observation days from mean boundary-layer profiles. However, turbulence statistics of wind speed components and temperature in the monsoon boundary layer for both days are generally greater than those observed in laboratory experiments or tropical and trade wind boundary layers in which a strong jet was not present. Analysis of high frequency wind, temperature and humidity data was made to obtain fluxes of momentum and heat. Magnitudes of the sensible and latent heat fluxes are three to five times larger than the values observed over the monsoon boundary layer over the Bay of Bengal. The turbulent kinetic energy budget over the Arabian Sea for 24 June indicates the importance of buoyancy, and to a lesser extent shear as the dominant term. Dissipation serves as the primary sink term.  相似文献   

Pollution effects on ecobiology of benthic polychaetes in Visakhapatnam Harbour (Bay of Bengal)     

A.V. Raman  P.N. Ganapati 《Marine pollution bulletin》1983,14(2):46-52

Rapid urbanization and industrialization of Visakhapatnam and construction of an outer harbour, restricting water flow, have markedly increased the organic load in the inner harbour. Studies of the physico-chemical and biological characteristics of six selected stations along a decreasing gradient of organic pollution have been carried out over a period of two years. The predominantly polychaete benthic fauna occurs in three distinct assemblages: Capitella capitata-Nereis glandicincta in the inner harbour; Cossura coasta-Tharyx marioni in the outer harbour; and a Chloeia-Axiothella-Chaetozone-Nephtys assemblage in the open sea.  相似文献   

Quasi-static deformation of a poroelastic half-space with anisotropic permeability by two-dimensional surface loads     

Sarva Jit Singh  Sunita Rani  Raman Kumar 《Geophysical Journal International》2007,170(3):1311-1327

An analytical solution is obtained of the fully coupled diffusion–deformation system of equations governing the quasi-static plane strain deformation of a poroelastic half-space with anisotropic permeability and compressible constituents. The stresses and the pore pressure are taken as the basic state variables. Displacements are obtained by integrating the coupled constitutive relations. The problem of surface loads is discussed in detail. Explicit analytical solutions are derived for normal line loading, shear line loading and normal strip loading. The permeability anisotropy is found to have a significant effect on the quasi-static deformation of the half-space. However, in the drained and undrained limits, the anisotropy has no effect. The stresses in the drained and undrained states are independent of the poroelastic parameters. Numerical computation of the pore pressure indicates that ignoring permeability anisotropy may lead to an overestimation of the pore pressure at points vertically below the point of normal loading. Further, anisotropy in permeability may lead to a dilution in the theoretical prediction of the Mandel–Cryer Effect.  相似文献