提孜那甫河流域地表太阳辐射估算及其影响因素分析     

张淑花  李新功  李奇虎  王默涵 《干旱区地理》2022,45(3):734-745

地表太阳辐射是地球表层主要能量来源,对地表能量平衡、能量交换以及生态水文过程等具有决定性意义。山区地形复杂,其地表太阳辐射时空差异较大且较难估算。采用适用于山区的地表太阳辐射模型对西北昆仑山提孜那甫河流域地表太阳辐射时空分布进行了估算,分析了该流域季节太阳辐射空间分布规律并探讨了地形和云2个重要因素对太阳辐射空间分布的影响。结果表明:（1） 地形因子中周围地形阻挡即地形开阔度（Sky view factor,SVF）与年总太阳辐射的关系最为显著,太阳辐射随SVF增加而增加。（2） 年总太阳辐射随着高程增加首先减少,再而随之增加。探究SVF随高程的变化,发现其与太阳辐射随高程的变化趋势较为一致,因此在山区复杂地形下地表太阳辐射估算中仅利用高程对其校正存在明显不足,需综合考虑地形效应。（3） 研究计算了季节云出现频率空间分布与太阳辐射空间分布的相关系数,结果表明夏季太阳辐射受云影响较其他季节显著。定量分析了地形因子以及云对地表太阳辐射空间分布影响的贡献率,周围地形阻挡SVF对地表太阳辐射空间分布的影响最大,高程和云次之。因此综合考虑地形和云对太阳辐射的影响在山区太阳辐射模拟中是非常必要的,研究可为山区地表太阳辐射模拟提供理论依据,并为山区生态水文过程研究提供方法支撑。  相似文献   

Estimation of Nash's IUH parameters using stochastic search algorithms     

S. Mohan  D. P. Vijayalakshmi 《水文研究》2008,22(17):3507-3522

In rainfall–runoff studies, it is often necessary to change the duration of a given unit hydrograph. Nash's Instantaneous Unit Hydrograph (IUH) is an ideal method that eliminates the hydrograph duration. This paper presents the results of the application of search algorithms, namely a genetic algorithm and hill climbing, to develop the IUH that minimizes the error between the observed and generated hydrographs. Also the performance of these methods has been compared with that of the classical method used for estimation of IUH, namely the method of moments. The genetic algorithm is a popular search procedure for function optimization that applies the mechanics of natural genetics and natural selection to explore a given search space. Hill climbing is an optimization technique that belongs to the family of local search and algorithms can be used to solve problems that have many solutions, with some solutions better than others. The results obtained from both the genetic algorithm and hill climbing algorithm for estimation of Nash's IUH parameters were compared with the results obtained by the method of moments for storms from two river basins that are located in different climatic regions. It was found that both the genetic algorithm and hill climbing provided improved and consistent results. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Equilibrium Structures of Rotationally and Tidally Distorted Polytropic Models of Stars     

A. K. Lal  S. Saini  C. Mohan  V. P. Singh 《Astrophysics and Space Science》2006,306(3):165-169

We propose suitable modifications in the concept of Roche equipotentials to account for the effect of mass distribution inside a star. The Kippenhahn and Thomas (1970) approach is used to incorporate the effects of rotational and tidal forces in the equations of stellar structure. The proposed method is applied to compute structures of certain rotationally and tidally distorted polytropic models.  相似文献   

Equilibrium Structures of Differentially Rotating and Tidally Distorted White Dwarf Models of Stars     

Arvind Kumar Lal  C. Mohan  V. P. Singh 《Astrophysics and Space Science》2006,301(1-4):51-60

In this paper we present a method for computing the equilibrium structures and various physical parameters of a primary component of the binary system assuming that the primary is more massive than the secondary and is rotating differentially according to the law of the w² = b₀ + b₁ × s² + b₂ × s⁴, w being the angular velocity of rotation of a fluid element distant s from the axis of rotation and b₀, b₁, b₂ suitably chosen numerical constants. This method utilizes the averaging approach of Kippenhahn and Thomas (1997) and the concept of Roche equipotentials in a manner earlier used by Mohan et al. (1997) to incorporate the effects of rotation and tidal distortions on the equilibrium structures of certain rotationally and tidally distorted stellar models. The use of the method has been illustrated by applying it to obtain the structures and some observable parameters of certain differentially rotating and tidally distorted binary systems whose primary component is assumed to be a white dwarf star.  相似文献   

Stellar contents of two young open clusters: NGC 663 and 654     

A. K. Pandey  K. Upadhyay  K. Ogura  Ram Sagar  V. Mohan  H. Mito  H. C. Bhatt  B. C. Bhatt 《Monthly notices of the Royal Astronomical Society》2005,358(4):1290-1308

UBVRI CCD photometry in a wide field around two young open clusters, NGC 663 and 654, has been carried out. Hα and polarimetric observations for the cluster NGC 654 have also been obtained. We use the photometric data to construct colour–colour and colour–magnitude diagrams, from which we can investigate the reddening, age, mass and evolutionary states of the stellar contents of the these clusters. The reddening across the cluster regions is found to be variable. There is evidence for anomalous reddening law in both clusters; however, more infrared and polarimetric data are needed to conclude about the reddening law. Both clusters are situated at about a distance of 2.4 kpc. Star formation in both clusters is found to be a continuous process. In the case of NGC 663, star formation seems to have taken place sequentially, in the sense that formation of low-mass stars precedes the formation of most massive stars. Whereas, in the case of NGC 654, formation of low-mass stars did not cease after the formation of most massive stars in the cluster.  相似文献   

GMRT observations of interstellar clouds in the 21cm line of atomic hydrogen     

Rekhesh Mohan  K. S. Dwarakanath  G. Srinivasan  Jayaram N. Chengalur 《Journal of Astrophysics and Astronomy》2001,22(1):35-50

Nearby interstellar clouds with high (|ν|≥10km s⁻¹) random velocities although easily detected in NaI and CaII lines have hitherto not been detected (in emission or absorption) in the HI 21cm line. We describe here deep Giant Metrewave Radio Telescope (GMRT) HI absorption observations toward radio sources with small angular separation from bright O and B stars whose spectra reveal the presence of intervening high random velocity CaII absorbing clouds. In 5 out of the 14 directions searched we detect HI 21cm absorption features from these clouds. The mean optical depth of these detections is ∼0.09 and FWHM is ∼10km s⁻¹, consistent with absorption arising from CNM clouds.  相似文献   

Use of Roche coordinates in the problems of small oscillations of tidally distorted stellar models     

C. Mohan  V. P. Singh 《Astrophysics and Space Science》1978,56(1):109-117

The system of Roche coordinates developed by Kopal to study the problems of stars in close binary systems has been used to study the problems of small oscillations of tidally distorted stars.  相似文献   

Effect of rotational and tidal distortions on the periods of small adiabatic oscillations of stellar models     

C. Mohan  V. P. Singh 《Astrophysics and Space Science》1982,85(1-2):83-98

Kopal's method of representing the inner structure of a rotationally and tidally-distorted star by a rotationally-and tidally-distorted Roche model has been used in conjunction with an averaging concept introduced by Kippenhahn and Thomas of representing the equipotential surfaces of a rotationally and tidally distorted stellar model by the equipotential surfaces of an equivalent spherical model to determine the combined effects of rotation and tidal distortion on the periods of small adiabatic oscillations of a stellar model.  相似文献   

An improved lunar moment of inertia determination: a proposed strategy     

Mohan P. Ananda  Alfred J. Ferrari  William L. Sjogren 《Earth, Moon, and Planets》1977,17(1):101-120

The current error of 0.0025 on the lunar homogeneity parameterI/MR ² is dominated by the uncertainties in theC ₂₀ andC ₂₂ gravity harmonics. This error level is equivalent to a 4.20 gm cm^–3 density uncertainty for a lunar interior model having a core 300 km in radius. Covariance analyses are performed using Doppler data from the relay satellite of the proposed Lunar Polar Orbiter mission to determine an optimum reduction strategy which obtains an order of magnitude improvement in the gravity estimates. Error studies show the long-arc reduction method obtains results which are an order of magnitude more accurate than the short-arc technique. The nominal 4000 km circular orbit of the relay satellite is very sensitive to the unmodeled effects of gravity harmonics of degree 5 through 9. Results from this orbital geometry indicate that it may not be possible to achieve the desired order of magnitude accuracy improvement. A modified orbit having the identical orbital conditions as the nominal one, but with a larger semi-major axis of 7000 km is studied. Results show the desired order of magnitude improvement can be achieved when a complete fourth degree and order model and some fifth and sixth degree terms are estimated while considering the unmodeled effects of the remaining harmonics through degree and order eight. Studies also show a 50% additional improvement inC ₂₂ can be achieved if differential differenced Doppler is also processed with the direct Doppler. The improved uncertainty inI/MR ² reduces the core density error from 4.20 gm cm^–3 to 0.1 gm cm^–3 for the case of a lunar density model having a 300 km core radius.Contribution #2885 of the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, U.S.A.  相似文献   

REE-HFSE distribution/partitioning between garnetiferous restites and TTG from Nademavinapura area,Western Dharwar craton     

S. N. Charan  E. V. S. S. K. Babu  S. M. Naqvi  J. G. Rana Prathap  M. Ram Mohan  D. Srinivasa Sarma 《Journal of the Geological Society of India》2009,73(3):371-378

The major part of the Peninsular Gneiss in Dharwar craton is made up of Trondjhemite-Tonalite-Granodiorite (TTG) emplaced at different periods ranging from 3.60 to 2.50 Ga. The sodic-silicic magma precursors of these rocks have geochemical features characteristic of partial melting of hydrated basalt. In these TTGs, enclaves of amphibolites (± garnet) are abundant. These restites are considered to be the residue of a basaltic crust after its partial melting. A detailed study of these (residue) enclaves reveals textures formed due to the process of partial melting. Major, trace and REE analysis of these residue enclaves and the melt TTGs and microprobe analysis of the coexisting minerals show partitioning of REE and HFSE between the precursor melt of TTGs and the upper amphibolite facies residues. Formation of garnetiferous amphibolites with biotite, Cpx and plagioclase consequent to melting, has squeezed the original MORB type of basaltic crust and given rise to the TTGs, depleted in Y, Yb, K₂O, MgO, FeO, TiO₂ and enriched in La, Th, U, Zr and Hf. Coevally during the process of melting, the hydrated basalt was depleted in Na₂O, Al₂O₃, LREE, Th, U and enriched in K₂O, MgO, Nb, Ti, Yb, Y, Sc, Ni, Cr and Co. Mineral chemistry of co-existing garnet-biotite and amphibole-plagioclase in these amphibolitic (restite) enclaves indicates an average temperature of 700 ± 50° C and pressure of 5 ± 1 Kbar. These data are inferred to indicate that during the garnet stability field metamorphism, effective fractionation of HREE and HFSE has taken place between the restites having Fe-Mg silicates, ilmenites and the extracted melt generated from the MORB type of hydrated basalt. These results are strongly substantiated by the reported melting experiments on hydrated basalts.  相似文献