An Improved Calibration of Satellite Altimetric Heights Using Tide Gauge Sea Levels with Adjustment for Land Motion   总被引：2，自引：0，他引：2  

Gary T. Mitchum 《Marine Geodesy》2000,23(3):145-166

Several major improvements to an existing method for calibrating satellite altimeters using tide gauge data are described. The calibration is in the sense of monitoring and correcting temporal drift in the altimetric time series, which is essential in efforts to use the altimetric data for especially demanding applications. Examples include the determination of the rate of change of global mean sea level and the study of the relatively subtle, but climatically important, decadal variations in basin scale sea levels. The improvements are to the method described by Mitchum (1998a), and the modifications are of two basic types. First, since the method depends on the cancellation of true ocean signals by differencing the altimetric data from the tide gauge sea level time series, improvements are made that produce a more complete removal of the ocean signals that comprise the noise for the altimetric drift estimation problem. Second, a major error source in the tide gauge data, namely land motion, is explicitly addressed and corrections are developed that incorporate space-based geodetic data (continuous GPS and DORIS measurements). The long-term solution, having such geodetic measurements available at all the tide gauges, is not yet a reality, so an interim solution is developed. The improved method is applied to the TOPEX altimetric data. The Side A data (August 1992?February 1999) are found to have a linear drift component of 0.55 + / 0.39 mm/yr, but there is also a significant quadratic component to the drift that is presently unexplained. The TOPEX Side B altimeter is estimated to be biased by 7.0 + / 0.7 mm relative to the Side A altimeter based on an analysis of the first 350 days of Side B data.  相似文献   

Measuring the environmental dimensions of human migration: The demographer's toolkit     

《Global Environmental Change》2014

In recent years, the empirical literature linking environmental factors and human migration has grown rapidly and gained increasing visibility among scholars and the policy community. Still, this body of research uses a wide range of methodological approaches for assessing environment–migration relationships. Without comparable data and measures across a range of contexts, it is impossible to make generalizations that would facilitate the development of future migration scenarios. Demographic researchers have a large methodological toolkit for measuring migration as well as modeling its drivers. This toolkit includes population censuses, household surveys, survival analysis and multi-level modeling. This paper's purpose is to introduce climate change researchers to demographic data and methods and to review exemplary studies of the environmental dimensions of human migration. Our intention is to foster interdisciplinary understanding and scholarship, and to promote high quality research on environment and migration that will lead toward broader knowledge of this association.  相似文献   

CSAMT在河南某铝土矿区深部勘查中的应用   总被引：1，自引：0，他引：1  

魏明君  赵金洲  杨长龙  刘国庆  宋双全 《物探与化探》2011,35(5):600-603

应用可控源音频大地电磁法,在河南新安县石寺—北冶铝土矿区进行隐伏铝土矿勘查。结果表明,利用该方法能够反演奥陶系灰岩古地形界面,推断铝土矿含矿岩系的赋存空间,预估算铝土矿潜在资源量;该方法探测深度较大,能满足深部铝土矿勘查需要;根据可控源方法断面电阻率等值线,可较清晰反映地层的产状,进而根据电阻率值划分地层。  相似文献   

PICARD: A novel code for the Galactic Cosmic Ray propagation problem     

《Astroparticle Physics》2014

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Density wave formation in differentially rotating disk galaxies: Hydrodynamic simulation of the linear regime     

《New Astronomy》2014

Most rapidly and differentially rotating disk galaxies, in which the sound speed (thermal velocity dispersion) is smaller than the orbital velocity, display graceful spiral patterns. Yet, over almost 240 yr after their discovery in M51 by Charles Messier, we still do not fully understand how they originate. In this first paper of a series, the dynamical behavior of a rotating galactic disk is examined numerically by a high-order Godunov hydrodynamic code. The code is implemented to simulate a two-dimensional flow driven by an internal Jeans gravitational instability in a nonresonant wave–“fluid” interaction in an infinitesimally thin disk composed of stars or gas clouds. A goal of this work is to explore the local and linear regimes of density wave formation, employed by Lin, Shu, Yuan and many others in connection with the problem of spiral pattern of rotationally supported galaxies, by means of computer-generated models and to compare those numerical results with the generalized fluid-dynamical wave theory. The focus is on a statistical analysis of time-evolution of density wave structures seen in the simulations. The leading role of collective processes in the formation of both the circular and spiral density waves (“heavy sound”) is emphasized. The main new result is that the disk evolution in the initial, quasilinear stage of the instability in our global simulations is fairly well described using the local approximation of the generalized wave theory. Certain applications of the simulation to actual gas-rich spiral galaxies are also explored.  相似文献   

黑洞X射线双星的类氢类氦铁K_α发射线     

许亚娣  刘当波  陈磊  徐海光  尤峻汉 《天文学报》2002,(3)

用径移主导吸积流模型(ADAF)不仅可以成功解释很多低吸积率天体的连续谱辐射,也可以说明X射线波段的谱线发射,而后者目前尚少有讨论.以黑洞X射线双星GX339-4处在低吸积率的宁静态情况为例,计算了它的铁线发射,表明在ADAF情况下的确可以产生足够强的可以在观测上检测的类氢和类氦铁Kα线.  相似文献   

Geometry of Spiral Galaxy Arms     

Jin He 《Astrophysics and Space Science》2003,283(2):305-310

The previous work (He, 2001) on image analysis of over one hundred nearby galaxies indicates that for any spiral galaxy image of small inclination there is evidence of two sets of iso-ratio curves in different scales which, like curvilineal coordinate lines, expand over different galaxy components. This result sets constraint on galaxy patterns and a general equation which carries this constraint is presented in the current paper. The equation has clear geometrical meaning. Its much simplified version which applies to galaxy arms, when solved, may be a guidance to understanding galaxy patterns. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Merging Massive Star Clusters as Building Blocks of Dwarf Galaxies?     

M. Fellhauer  P. Kroupa 《Astrophysics and Space Science》2002,281(1-2):355-358

Recent spectroscopic observations of galaxies in the Fornax-Cluster reveal nearly unresolved ‘star-like’ objects with red-shifts appropriate to the Fornax-Cluster. These objects have intrinsic sizes of ≈ 100 pc and absolute B-band magnitudes in the range - 14 < M_B < -11.5 mag and lower limits for the central surface brightness μ_B ≥ 23 mag/arcsec² (Phillipps et al., 2001, Hilker et al., 1999), and so appear to constitute a new population of ultra-compact dwarf galaxies (UCDs). Such compact dwarfs were predicted to form from the amalgamation of stellar super-clusters (= clusters of star clusters; not to confuse with super stellar clusters (SSC)) by P. Kroupa (1998), which are rich aggregates of young massive star clusters (YMCs) that can form in collisions between gas-rich galaxies. Here we present the evolution of super-clusters in a tidal field. The YMCs merge on a few super-cluster crossing times. Super-clusters that are initially as concentrated and massive as Knot S in the interacting Antennae galaxies (Whitmore et al., 1999) evolve to merger objects that are long-lived and show properties comparable to the newly discovered UCDs. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

Exchange Processes in a Multi-Phase ISM     

Stefan Harfst  Christian Theis  Gerhard Hensler 《Astrophysics and Space Science》2002,281(1-2):313-314

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Star cluster disruption by giant molecular clouds     

M. Gieles  S. F. Portegies Zwart  H. Baumgardt  E. Athanassoula  H. J. G. L. M. Lamers  M. Sipior  J. Leenaarts 《Monthly notices of the Royal Astronomical Society》2006,371(2):793-804

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