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11.
12.
Farook Rahaman Subenoy Chakraborty Jayanta Kr. Bera 《Astrophysics and Space Science》2002,281(3):595-600
The inhomogeneous Bianchi-I model based on Lyra's geometry has been studied in the cosmological theory in presence of a massless
inhomogeneous scalar field whose potential has a flat part. The field equations are solved using separation of variables and
it is shown that one of the time part of the field equations are solvable for any arbitrary other cosmic scale function. Solutions
for a particular form of cosmic scale (time part) is presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
14.
Equilibrium configuration of the upper Main-Sequence stars, with significant radiation pressure and having an interior magnetic field (matching with an external dipole field) has been cosidered. The structural parameters have been calculated for low and high magnetic fields by using a first-order perturbation method and a modified perturbation technique respectively. With the increase of radiation pressure, the star is seen to become more centrally condensed. 相似文献
15.
Rosine Lallement Bertaux Jean-Loup Karöly Szegö Szilvia Nemeth 《Earth, Moon, and Planets》2002,90(1-4):67-76
For a few months around perihelion, thecentral part of the Hale–Bopp hydrogencloud has been optically thick to thesolar Lyα
radiation, and hassignificantly reduced the solar flux availablefor the resonance glow of interstellarhydrogen beyond the
comet. This shadowing effecton the interstellar gas is the first everobserved comet shadow. It is modeled andcompared with
SWAN observations. Shadowmodelling will help to constrain the cometwater production and radiative transfer effectsin the interstellar
ionisation cavity. 相似文献
16.
The aeolian sedimentation record of the Thar desert 总被引:1,自引:0,他引:1
A review of the aeolian sedimentary record of the Thar desert is presented. This includes a regional survey of the major dune
forms, their genesis and their relationship to climate and other regional landforms. A key aspect of this work is the chronometry
of the dunes using luminescence methods. Luminescence dating of sand has enabled quantification of the duration of the phases
of sand aggradation and quiescence, time scales of dune migration and the dating of pedogenic carbonates. We demonstrate that
the conventional wisdom of synchronicity of dune aggradation with glacial epoch is not true in the context of Thar sands and
here only a short durationwindow of opportunity existed for dune aggradation. Luminescence ages further suggest that this window occurred during a transitional climatic
regime from glacial to interglacial about 4–10 ka after the glacial epoch. Other inferences included are that:
相似文献
– | • the aeolian activity in the Thar began over > 150 ka, resolving that Thar is not of anthropogenic origin as suggested previously; |
– | • the present spatial extent of the aeolian activity in the Thar is in a contracted stage compared to that in the geological past, which refutes the arguments on its rapid north-eastward expansion; |
– | • the current dune migration rates in areas of significant human-induced disturbances are much higher than during the geological past; |
– | • the monsoon activity in the Thar varied significantly, from being minimal during the isotopic marine stages 4 and 2 to being close to the present during stage 3; |
– | • on shorter time scales the dune activities correlated with the lacustrine records of the region with a phase difference of a few centuries and a periodicity of ∼ 1500 years; |
– | • the sand aggradation climate in the southern margin in Gujarat gradually shrank northwards such that in general dunes older than 10 ka are seen in the extreme southern margin and dunes younger than 2ka ages occur mostly in the western part of Rajasthan. |
17.
Probabilistic prediction of Indian summer monsoon rainfall using global climate models 总被引:1,自引:0,他引:1
Makarand A. Kulkarni Nachiketa Acharya Sarat C. Kar U. C. Mohanty Michael K. Tippett Andrew W. Robertson Jing-Jia Luo Toshio Yamagata 《Theoretical and Applied Climatology》2012,107(3-4):441-450
Probabilistic seasonal predictions of rainfall that incorporate proper uncertainties are essential for climate risk management. In this study, three different multi-model ensemble (MME) approaches are used to generate probabilistic seasonal hindcasts of the Indian summer monsoon rainfall based on a set of eight global climate models for the 1982–2009 period. The three MME approaches differ in their calculation of spread of the forecast distribution, treated as a Gaussian, while all three use the simple multi-model subdivision average to define the mean of the forecast distribution. The first two approaches use the within-ensemble spread and error residuals of ensemble mean hindcasts, respectively, to compute the variance of the forecast distribution. The third approach makes use of the correlation between the ensemble mean hindcasts and the observations to define the spread using a signal-to-noise ratio. Hindcasts are verified against high-resolution gridded rainfall data from India Meteorological Department in terms of meteorological subdivision spatial averages. The use of correlation for calculating the spread provides better skill than the other two methods in terms of rank probability skill score. In order to further improve the skill, an additional method has been used to generate multi-model probabilistic predictions based on simple averaging of tercile category probabilities from individual models. It is also noted that when such a method is used, skill of probabilistic forecasts is improved as compared with using the multi-model ensemble mean to define the mean of the forecast distribution and then probabilities are estimated. However, skill of the probabilistic predictions of the Indian monsoon rainfall is too low. 相似文献
18.
Jayanta K. Bhattacharjee Atri Bhattacharya Tapas K. Das Arnab K. Ray 《Monthly notices of the Royal Astronomical Society》2009,398(2):841-852
In a novel approach to studying viscous accretion flows, viscosity has been introduced as a perturbative effect, involving a first-order correction in the α-viscosity parameter. This method reduces the problem of solving a second-order non-linear differential equation (Navier–Stokes equation) to that of an effective first-order equation. Viscosity breaks down the invariance of the equilibrium conditions for stationary inflow and outflow solutions, and distinguishes accretion from wind. Under a dynamical systems classification, the only feasible critical points of this 'quasi-viscous' flow are saddle points and spirals. On large spatial scales of the disc, where a linearized and radially propagating time-dependent perturbation is known to cause a secular instability, the velocity evolution equation of the quasi-viscous flow has been transformed to bear a formal closeness with Schrödinger's equation with a repulsive potential. Compatible with the transport of angular momentum to the outer regions of the disc, a viscosity-limited length-scale has been defined for the full spatial extent over which the accretion process would be viable. 相似文献
19.
Behera Rashmisikha Kar Abhipsa Das Manas Ranjan Panda Prachi Prava 《Natural Hazards》2019,96(2):731-751
Natural Hazards - The 485-km-long coastline of Odisha, a state in the northeastern part of the Indian peninsula, is potentially vulnerable to several disaster events that take place frequently. In... 相似文献
20.
Theoretical and Applied Climatology - Coupled ocean atmosphere global climate models are increasingly being used for seasonal scale simulation of the South Asian monsoon. In these models, sea... 相似文献