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1.
Yehouda Enzel Rivka Amit Uri Dayan Onn Crouvi Ron Kahana Baruch Ziv David Sharon 《Global and Planetary Change》2008,60(3-4):165-192
Modern-day synoptic-scale eastern Mediterranean climatology provides a useful context to synthesize the diverse late Pleistocene (60–12 ka) paleohydrologic and paleoenvironmental indicators of past climatic conditions in the Levant and the deserts to its south and east. We first critically evaluate, extract, and summarize paleoenvironmental and paleohydrologic records. Then, we propose a framework of eastern Mediterranean atmospheric circulation features interacting with the morphology and location of the southeast Mediterranean coast. Together they strongly control the spatial distribution of rainfall and wind pattern. This cyclone–physiography interaction enforces the observed rainfall patterns by hampering rainfall generation south and southeast of the latitude of the north Sinai coast, currently at 31°15′.The proposed framework explains the much-increased rains in Lebanon and northern Israel and Jordan as deduced from pollen, rise and maintenance of Lake Lisan, and speleothem formation in areas currently arid and semiarid. The proposed framework also accounts for the southward and eastward transition into semiarid, arid, and hyperarid deserts as expressed in thick loess accumulation at the deserts' margins, dune migration from west to east in the Sinai and the western Negev, and the formation of hyperarid (< 80 mm yr− 1) gypsic–salic soils in the southern Negev and Sinai. Our climatic synthesis explains the hyperarid condition in the southern Negev, located only 200–250 km south of the much-increased rains in the north, probably reflecting a steeper rainfall gradient than the present-day gradient from the wetter Levant into its bordering southern and eastern deserts.At present, the rainiest winter seasons in Lebanon and northern and central Israel are associated with more frequent (+ 20%), deeper Cyprus Lows traversing the eastern Mediterranean at approximately the latitude of southern Turkey. Even these wettest years in northern Israel do not yield above average annual rainfall amounts in the hyperarid southern Negev. This region is mainly influenced by the Active Red Sea Troughs that produce only localized rains. The eastern Mediterranean Cyprus Lows also produce more dust storms and transport higher amounts of suspended dust to the loess area than any other atmospheric pattern. Concurrent rainfall and dust are essential to the late Pleistocene formation of the elongated thick loess zone along the desert northern margin. Even with existing dust storms, the lack of rain and very sparse vegetation account for the absence of late Pleistocene loess sequences from the southern Negev and the formation of hyperarid soils.When the north Sinai coast shifted 30–70 km northwest due to last glacial global sea level lowering, the newly exposed coastal areas supplied the sand and dust to these active eastern Mediterranean cyclones. This enforced the latitude of the northern boundary of the loess zone to be directly due east of the LGM shoreline. This shift of coast to the northwest inhibited rainfall in the southern Levant deserts and maintained their hyperaridity. Concurrently, frequent deep eastern Mediterranean Cyprus Lows were funneled along the northern Mediterranean increasing (probably doubling) the rains in central and northern Israel, Lebanon, southwestern Syria and northern Jordan. These storms and rains formed lakes, forests, and speleothems only a short distance north of the deserts in the southern Levant. 相似文献
2.
P. Kenneth Seidelmann B. A. Archinal M. F. A’hearn A. Conrad G. J. Consolmagno D. Hestroffer J. L. Hilton G. A. Krasinsky G. Neumann J. Oberst P. Stooke E. F. Tedesco D. J. Tholen P. C. Thomas I. P. Williams 《Celestial Mechanics and Dynamical Astronomy》2007,98(3):155-180
Every three years the IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the
directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report
introduces improved values for the pole and rotation rate of Pluto, Charon, and Phoebe, the pole of Jupiter, the sizes and
shapes of Saturn satellites and Charon, and the poles, rotation rates, and sizes of some minor planets and comets. A high
precision realization for the pole and rotation rate of the Moon is provided. The expression for the Sun’s rotation has been
changed to be consistent with the planets and to account for light travel time 相似文献
3.
Vladimir A. Krasnopolsky 《Planetary and Space Science》2010,58(12):1507-1515
There are observational and theoretical evidences both in favor of and against hydrodynamic escape (HDE) on Titan, and the problem remains unsolved. A test presented here for a static thermosphere does not support HDE on Titan and Triton but favors HDE on Pluto. Cooling of the atmosphere by the HCN rotational lines is limited by rotational relaxation above 1100 km and self-absorption below 900 km on Titan. HDE can affect the structure and composition of the atmosphere and its evolution. Hydrocarbon, nitrile, and ion chemistries are strongly coupled on Titan, and attempts to calculate them separately may result in significant errors. Here we apply our photochemical model of Titan’s atmosphere and ionosphere to the case of no hydrodynamic escape. Our model is still the only after-Cassini self-consistent model of coupled neutral and ion chemistry. The lack of HDE is a distinct possibility, and comparing models with and without HDE is of practical interest. The mean difference between the models and the neutral and ion compositions observed by INMS are somewhat better for the model with HDE. A reaction of NH2 with H2CN suggested by Yelle et al. (2009) reduces but does not remove a significant difference between the ammonia abundances in the models and INMS observations. Losses of methane and nitrogen and production and deposition to the surface of hydrocarbons and nitriles are evaluated in the model, along with lifetimes and evolutionary aspects. 相似文献
4.
Fouad Sahraoui Melvyn L. Goldstein Alain Roux Patrick Canu Nicole Cornilleau-Wehrlin Thierry Dudok De Wit Khurom Kiyani 《Planetary and Space Science》2011,59(7):585-591
Investigating space plasma turbulence from single-point measurements is known to be characterized by unavoidable ambiguities in disentangling temporal and spatial variations. Solving this problem has been one of the major goals of the Cluster mission. For that purpose multipoint measurements techniques, such as the k-filtering, have been developed. Such techniques combine several time series recorded simultaneously at different points in space to estimate the corresponding energy density in the wavenumber space. Here we apply the technique to both simulated and Cluster magnetometer data in the solar wind (SW) and investigate the errors and limitations that arise due to the separation of the spacecraft and the quality of the tetrahedral configuration. Specifically, we provide an estimation of the minimum and maximum scales that can be accurately measured given a specific distance between the satellites and show the importance of the geometry of the tetrahedron and the relationship of that geometry to spatial aliasing. We also present recent results on characterizing small scale SW turbulence and provide scientific arguments supporting the need of new magnetometers having better sensitivity than the existing ones. Throughout the paper we emphasize technical challenges and their solutions that can be considered for a better preparation of the Cross-Scale mission. 相似文献
5.
The central and outer components from the radiation beam of a pulsar are called the core and cone components, respectively. It was found in some early researches that a proportion of 0.7 exists between the widths of core and cone components of pulsars. 33 pulsars with signi?cant core and cone components are selected to verify it. The component separations are made by ?tting the integrated pulse pro?les of these pulsars with Gaussian functions, so as to obtain the widths and errors of all the core and cone components. The relation between the widths of core and cone components is investigated for the triple-peaked and quintuple-peaked pulsars, respectively. We ?nd that there are no signi?cant differences between the widths of core and cone components, the proportion of between the widths of core and cone components that reported by previous studies does not exist. 相似文献
6.
Report of the IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements: 2003 总被引：1，自引：1，他引：0
P. K. Seidelmann B. A. Archinal M. F. A’Hearn D. P. Cruikshank J. L. Hilton H. U. Keller J. Oberst J. L. Simon P. Stooke D. J. Tholen P. C. Thomas 《Celestial Mechanics and Dynamical Astronomy》2005,91(3-4):203-215
Every three years the IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the
directions of the north poles of rotation and the prime meridians of the planets, satellites, and asteroids. This report introduces
a system of cartographic coordinates for asteroids and comets. A topographic reference surface for Mars is recommended. Tables
for the rotational elements of the planets and satellites and size and shape of the planets and satellites are not included,
since there were no changes to the values. They are available in the previous report (Celest. Mech. Dyn. Astron., 82, 83–110, 2002), a version of which is also available on a web site. 相似文献
7.
As shown by statistical results, in the 23rd solar activity cycle the variation of the latitudes of rotating sunspots with time exhibits a butterfly pattern. We have studied the variations with phase for the mean square errors among the 4 fitting curves of the 2 wings of the butterfly diagram of sunspots and the 2 wings of the butterfly diagram of rotating sunspots in the 23rd solar activity cycle. The results show that a systematic time delay exists not only between the northern and southern hemispheres of the butterfly diagram of sunspots, but also between the northern and southern hemispheres of the butterfly diagram of rotating sunspots, even between the butterfly diagrams of the sunspots and rotating sunspots in the same hemisphere. This means that the 23rd-cycle sunspot activities in the northern and southern hemispheres happened not simultaneously, that a systematic time delay or advance (phase difference) exists between the northern and southern hemispheres, that the southern hemisphere lags behind the northern hemisphere, that a phase difference exists between the butterfly diagram of rotating sunspots and the butterfly diagram of sunspots in the 23rd cycle, and that the butterfly diagram of rotating sunspots lags behind that of sunspots. The observed delay is a little less than the theoretical value predicted by the dynamo model. 相似文献
8.
The Atmospheres Node of the International Outer Planets Watch (IOPW, formerly known as International Jupiter Watch; Russell et al., 1990) intends to encourage and coordinate the imaging observations and study of the atmospheres of the Giant Planets. The main activity of the atmospheres node is to provide an interaction between the professional and amateur astronomical communities maintaining a large database of images of the giant planets (primarily Jupiter and Saturn but with increasing contributions of Uranus and Neptune too). The observational datasets of Jupiter and Saturn correspond to images obtained in the visible range (300 nm-1 μm), during the last decade, most of them performed by amateur observers. We here describe the organization and structure of the database as posted on the Internet and in particular the PVOL software (Planetary Virtual Observatory Laboratory) designed to manage the site in the spirit of the Virtual Observatory projects. We also describe with examples the important role of the amateur-professional collaboration in the study of the atmospheres of Jupiter and Saturn in an epoch of large telescopes and spacecraft observations of both planets. 相似文献
9.
喷流的研究是天文学和天体物理学中最使人兴趣的课题之一。在本文中，陈述了河外射电源中喷流在现阶段的观测阶段，讨论了某些典型的高能天体中喷流的特性。第一部分所涉及的内容包括喷流的定义，产生和传播；也包括喷流的不对称性和统一的解释模式的讨论。 相似文献
10.
金属丰度是表征星系特征的重要参量,对于理解星系的形成与演化具有重要意义。随着观测设备的不断完善与发展,已经获得越来越多的星系(包括近邻星系、中等红移及高红移星系)金属丰度的观测资料。在光致电离模型方面也取得了很大进展．这些对于理解星系中金属及恒星成分的累积历史有非常重要的作用。有多种方法可以用来估计星系的金属丰度(主要是星际介质中气相的O丰度),介绍和评述了估计星系的O丰度的多种方法,包括电子温度的方法、R23方法以及其他一些“强线”比值的方法,并给出了相应的解析公式,同时介绍了电离星云的物理本质及由光致电离模型估计星系金属丰度的方法,还给出了估计星系的C和N元素丰度的方法。 相似文献
11.
12.
At the great city of Tikal, the ancient Maya placed and oriented their ceremonial architecture and monuments in accordance with cosmological principles. Its earliest ceremonial plaza, the Mundo Perdido, is one of the oldest pre-Classic E-Groups of the Petén, the astronomical utility of which has been a topic of debate by archeologists and archaeoastronomers alike over the past century. In 1988, Aveni and Hartung surveyed the great temples of Tikal and revealed the relationship between their astronomical and dynastic aspects. Yet, over the intervening decades breakthroughs in the decipherment of the Maya glyphs have greatly increased our understanding of Tikal's dynastic history while interpretations in the field of archaeoastronomy have become more rigorous. For instance, more recent surveys and interpretations by Ŝprajc (2021a, 2021b) have demonstrated the importance of the Maya ritual calendar in the placement and orientation of ceremonial public architecture. The aim of this paper is to reassess this earlier fieldwork in archaeoastronomy, provide recent corroborative measurements of the orientation of key buildings, and provide a cohesive summation of the cosmological principles found in the design and construction of the city of Tikal. 相似文献
13.
LAMOST观测控制系统体系结构设计 总被引：1，自引：0，他引：1
由于大天区面积多目标光纤光谱天文望远镜(LAMOST)系统非常复杂,系统研制的时间比较长,系统建成后有相当长的使用年限,就要求观测控制系统(OCS)有足够长的生命周期(使用、维护及升级),可扩展性和良好的可维护性,因此系统需要一个合理健全、内在一致的体系结构。根据OCS的建模和体系结构的概念,在对OCS建模及参考各种体系结构模式的基础上完成了基于构件的层状的OCS系统体系构架,融合了MVC,代理等体系结构模式。详细讨论了OCS体系结构的静态模型和动态模型,并在OCS的1级系统实现了此体系结构。 相似文献
14.
BPM短波授时台新的时频监控系统 总被引：1，自引：1，他引：0
陕西天文台BPM短波授时台搬迁后 ,其时频控制与监测工作从原BPM发播钟房转为由监控室监控钟房承担。介绍了新的控制系统原理与方法 ,并对发播的BPM时号精度作了分析。 相似文献
15.
Beata Gruszka 《Global and Planetary Change》2001,28(1-4)
Pleistocene glaciolacustrine sediments of the Kleszczów Graben (the Be
chatów outcrop, central Poland) record the origin, development, and decay of a glacial lake formed in the area of a subsiding basin during the advance of the Elsterian ice sheet. The sediments represent a transition from glaciofluvial to glaciolacustrine facies at the bottom part, and from glaciolacustrine to glacial facies at the top. The glaciolacustrine facies represent a few environments inside the lake basin, from the marginal sub-aqueous slope through the bottom part to the sub-aqueous fan. The contact of the glaciolacustrine facies and the overlying glacial till is erosional, and implies that a considerable part of the shallow-water lake facies was eroded.The lake existed for not longer than 600 years, but its development proceeded under the conditions of the Kleszczów Graben subsidence and the approach of the Elsterian ice sheet. Both factors influenced the sedimentation processes. The tectonic and climatic factors were recognised on the basis of facies analysis of lithofacies associations, and of their vertical and lateral changes. 相似文献
16.
时间频率量的特征及其对时频系统建设的影响 总被引：2，自引：1，他引：1
分析了物理量测量中时间频率量的特点，主要有：时间的流逝性；其基准是自然基准；时间和频率既密切相关又有区别；时间频率具有最高的测量精细度(分辨率)与准确度；其计量标准可通过电磁波发播；其测量精确度与测量时间有关。另外，从基准、守时、授时、时间频率设备的研制、生产和队伍建设等方面阐发了这些特点对时间频率系统建设的影响。 相似文献
17.
守时工作进展 总被引：11，自引：0，他引：11
随着近5年时间传递技术(多通道GPS／GLONASS CV、TWSTFT、GPS P3 CV)和原子时算法的发展，国际原子时TAI和各国的守时工作有了较大的进展，中国科学院国家授时中心(NTSC)和国内其他时间实验室的工作也不例外。介绍国际权度局(BIPM)时间部有关2000～2003年TAI的研究进展，以及NTSC和国际、国内某些时间实验室守时工作简况。另外，自2000年以来国际上对UTC之未来的争论很激烈，因此就2003年5月28～30日在意大利都灵市举行的“UTC的未来”研讨会的情况也作一些介绍，以便国内天体测量相关学术领域的同行们对这些发展有一个基本的了解。 相似文献
18.
Feedback from supernovae (SNe) and from active galactic nuclei (AGN) accom-panies the history of star formation and galaxy evolution. We present an analytic model to explain how and when the SNe and AGN exert their feedback effects on the star formation and galaxy evolution processes. By using SNe and AGN kinetic feedback mechanisms based on the Lambda Cold Dark Matter (LCDM) model, we explore how these feedback mecha-nisms affect the star formation history (SFH), the Near-Infrared Background (NIRB) flux and the cosmological reionization. We find the values of the feedback strengths, ∈AGN =1.0+0.50.3and ∈SN=0.04+0.02-0.02, can provide a reasonable explanation of most of the observational re-suits, and that the AGN feedback effect on star formation history is quite different from the SNe feedback at high redshifts. Our conclusions manifest quantitatively that these feedback effects decrease star formation rate density (SFRD) and the NIRB flux (in 1.4 - 4.0μm), and postpone the time of completion of the cosmological reionization. 相似文献
19.
The cometary meteoroid ejection model of Jones and Brown [Physics, Chemistry, and Dynamics of Interplanetary Dust, ASP Conference Series
104 (1996b) 137] was used to simulate ejection from comets 55P/Tempel-Tuttle during the last 12 revolutions, and the last 9 apparitions
of 109P/Swift-Tuttle. Using cometary ephemerides generated by the Jet Propulsion Laboratory’s (JPL) HORIZONS Solar System
Data and Ephemeris Computation Service, two independent ejection schemes were simulated. In the first case, ejection was simulated
in 1 h time steps along the comet’s orbit while it was within 2.5 AU of the Sun. In the second case, ejection was simulated
to occur at the hour the comet reached perihelion. A 4th order variable step-size Runge–Kutta integrator was then used to
integrate meteoroid position and velocity forward in time, accounting for the effects of radiation pressure, Poynting–Robertson
drag, and the gravitational forces of the planets, which were computed using JPL’s DE406 planetary ephemerides. An impact
parameter (IP) was computed for each particle approaching the Earth to create a flux profile, and the results compared to
observations of the 1998 and 1999 Leonid showers, and the 1993 and 2004 Perseids. 相似文献