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311.
Advances in modeling gradual solar energetic particle events 总被引:1,自引:0,他引:1
D. Lario 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2005,36(12):2279-2288
Solar energetic particles pose one of the most serious hazards to space probes, satellites and astronauts. The most intense and largest solar energetic particle events are closely associated with fast coronal mass ejections able to drive interplanetary shock waves as they propagate through interplanetary space. The simulation of these particle events requires knowledge of how particles and shocks propagate through the interplanetary medium, and how shocks accelerate and inject particles into interplanetary space. Several models have appeared in the literature that attempt to model these energetic particle events. Each model presents its own simplifying assumptions in order to tackle the series of complex phenomena occurring during the development of such events. The accuracy of these models depends upon the approximations used to describe the physical processes involved in the events. We review the current models used to describe gradual solar energetic particle events, their advances and shortcomings, and their possible applications to space weather forecasting. 相似文献
312.
This review is devoted to ponderomotive forces and their importance for the acceleration of charged particles by electromagnetic
waves in space plasmas. Ponderomotive forces constitute time-averaged nonlinear forces acting on a media in the presence of
oscillating electromagnetic fields. Ponderomotive forces represent a useful analytical tool to describe plasma acceleration.
Oscillating electromagnetic fields are also related with dissipative processes, such as heating of particles. Dissipative
processes are, however, left outside these discussions. The focus will be entirely on the (conservative) ponderomotive forces
acting in space plasmas.
The review consists of seven sections. In Section 1, we explain the rational for using the auxiliary ponderomotive forces
instead of the fundamental Lorentz force for the study of particle motions in oscillating fields. In Section 2, we present
the Abraham, Miller, Lundin–Hultqvist and Barlow ponderomotive forces, and the Bolotovsky–Serov ponderomotive drift. The hydrodynamic,
quasi-hydrodynamic, and ‘`test-particle’' approaches are used for the study of ponderomotive wave-particle interaction. The
problems of self-consistency and regularization are discussed in Section 3. The model of static balance of forces (Section
4) exemplifies the interplay between thermal, gravitational and ponderomotive forces, but it also introduces a set of useful
definitions, dimensionless parameters, etc. We analyze the Alfvén and ion cyclotron waves in static limit with emphasis on
the specific distinction between traveling and standing waves. Particular attention has been given to the impact of traveling
Alfvén waves on the steady state anabatic wind that blows over the polar regions (Section~5). We demonstrate the existence
of a wave-induced cold anabatic wind. We also show that, at a critical point, the ponderomotive acceleration of the wind is
a factor of 3 greater than the thermal acceleration. Section 6 demonstrates various manifestations of ponderomotive forces
in the Earth's magnetosphere, for instance the ionospheric plasma acceleration and outflow. The polar wind and the auroral
density cavities are considered in relation to results from the Freja and Viking satellites. The high-altitude energization
and escape of ions is discussed. The ponderomotive anharmonicity of standing Alfvén waves is analyzed from ground based ULF
wave measurements. The complexity of the many challenging problems related with plasma processes near the magnetospheric boundaries
is discussed in the light of recent Cluster observations. At the end of Section 6, we consider the application of ponderomotive
forces to the diversity of phenomena on the Sun, in the interstellar environment, on newborn stars, pulsars and active galaxies.
We emphasize the role of forcing of magnetized plasmas in general and ponderomotive forcing in particular, presenting some
simple conceivable scenarios for massive outflow and jets from astrophysical objects. 相似文献
313.
The ionic charge distributions of solar energetic particles (SEP) as observed in interplanetary space provide fundamental
information about the origin of these particles, and the acceleration and propagation processes at the Sun and in interplanetary
space. In this paper we review the measurements of ionic charge states of energetic particles in interplanetary space and
discuss their implication for our understanding of SEP sources, and acceleration and propagation processes. 相似文献
314.
315.
大迎角气动导数对飞机横船向飞行品质的影响 总被引:1,自引:0,他引:1
以第三代战斗机为例,采用等效系统方法,通过计算并讨论飞行品质指标滚转模态时间常数(Tr),荷幸滚模态的阻尼比和频率及驾驶员座位处的加速度随气动导数的改变特征,研究在失束宛角前大迎角气动对具有现代控制系统的飞机横向飞行品质的影响。结果表明,气动导数Clδa和lp主要影响Tr及ayp;Cnδr,Cnδr,Cnr,Cnβ及Cyβ主要影响ξn或ωn;Clβ的影响相对较小。 相似文献
316.
Ioannis A. Daglis 《Space Science Reviews》2006,124(1-4):183-202
This chapter reviews the current understanding of ring current dynamics. The terrestrial ring current is an electric current
flowing toroidally around the Earth, centered at the equatorial plane and at altitudes of ∼10,000 to 60,000 km. Enhancements
in this current are responsible for global decreases in the Earth’s surface magnetic field, which have been used to define
geomagnetic storms. Intense geospace magnetic storms have severe effects on technological systems, such as disturbances or
even permanent damage of telecommunication and navigation satellites, telecommunication cables, and power grids. The main
carriers of the ring current are positive ions, with energies from ∼1 keV to a few hundred keV, which are trapped by the geomagnetic
field and undergo an azimuthal drift. The ring current is formed by the injection of ions originating in the solar wind and
the terrestrial ionosphere into the inner magnetosphere. The injection process involves electric fields, associated with enhanced
magnetospheric convection and/or magnetospheric substorms. The quiescent ring current is carried mainly by protons of predominantly
solar wind origin, while active processes in geospace tend to increase the abundance (both absolute and relative) of O+ ions, which are of ionospheric origin. During intense geospace magnetic storms, the O+ abundance increases dramatically. This increase has been observed to occur concurrently with the rapid intensification of
the ring current in the storm main phase and to result in O+ dominance around storm maximum. This compositional change can affect several dynamic processes, such as species-and energy-dependent
charge-exchange and wave-particle scattering loss. 相似文献
317.
318.
319.
文章分3篇10章详细介绍了稳态加速度模拟试验设备--离心机的设计.上篇对稳态加速度环境及其效应、相关试验方法和国家标准作了阐述;中篇(上)系统介绍了国内外离心机发展的历史,提供了较为全面具体的离心机结构概况,并对它们逐一进行小结与点评;中篇(下)对离心机进行基本理论分析,研究总体设计和部件设计问题,提出离心机设计原则及其计算方法;下篇通过一个国家"七五"科技攻关项目的实践作为实例,提供读者作设计参考.在文章中,作者对多年来积累的技术资料和实践心得进行了系统的整理和归纳,梳理出一条在离心机研制中科学的设计思路和实用的工作程序.该文章对相关领域的研究人员和技术人员会有启发和帮助,同时对其他同类设备的设计也有触类旁通的作用.文章主要探讨的对象是中型、大型、特大型航空航天物体离心机,土工离心机和载人离心机. 相似文献
320.
R. Lundin D. Winningham S. Barabash R. Frahm D. Brain H. Nilsson M. Holmström M. Yamauchi J. R. Sharber J.-A. Sauvaud A. Fedorov K. Asamura H. Hayakawa A. J. Coates Y. Soobiah C. Curtis K. C. Hsieh M. Grande H. Koskinen E. Kallio J. Kozyra J. Woch M. Fraenz J. Luhmann S. Mckenna-Lawler S. Orsini P. Brandt P. Wurz 《Space Science Reviews》2006,126(1-4):333-354
Aurora is caused by the precipitation of energetic particles into a planetary atmosphere, the light intensity being roughly proportional to the precipitating particle energy flux. From auroral research in the terrestrial magnetosphere it is known that bright auroral displays, discrete aurora, result from an enhanced energy deposition caused by downward accelerated electrons. The process is commonly referred to as the auroral acceleration process. Discrete aurora is the visual manifestation of the structuring inherent in a highly magnetized plasma. A strong magnetic field limits the transverse (to the magnetic field) mobility of charged particles, effectively guiding the particle energy flux along magnetic field lines. The typical, slanted arc structure of the Earth’s discrete aurora not only visualizes the inclination of the Earth’s magnetic field, but also illustrates the confinement of the auroral acceleration process. The terrestrial magnetic field guides and confines the acceleration processes such that the preferred acceleration of particles is frequently along the magnetic field lines. Field-aligned plasma acceleration is therefore also the signature of strongly magnetized plasma. This paper discusses plasma acceleration characteristics in the night-side cavity of Mars. The acceleration is typical for strongly magnetized plasmas – field-aligned acceleration of ions and electrons. The observations map to regions at Mars of what appears to be sufficient magnetization to support magnetic field-aligned plasma acceleration – the localized crustal magnetizations at Mars (Acuña et al., 1999). Our findings are based on data from the ASPERA-3 experiment on ESA’s Mars Express, covering 57 orbits traversing the night-side/eclipse of Mars. There are indeed strong similarities between Mars and the Earth regarding the accelerated electron and ion distributions. Specifically acceleration above Mars near local midnight and acceleration above discrete aurora at the Earth – characterized by nearly monoenergetic downgoing electrons in conjunction with nearly monoenergetic upgoing ions. We describe a number of characteristic features in the accelerated plasma: The “inverted V” energy-time distribution, beam vs temperature distribution, altitude distribution, local time distribution and connection with magnetic anomalies. We also compute the electron energy flux and find that the energy flux is sufficient to cause weak to medium strong (up to several tens of kR 557.7 nm emissions) aurora at Mars. Monoenergetic counterstreaming accelerated ions and electrons is the signature of field-aligned electric currents and electric field acceleration. The topic is reasonably well understood in terrestrial magnetospheric physics, although some controversy still remains on details and the cause-effect relationships. We present a potential cause-effect relationship leading to auroral plasma acceleration in the nightside cavity of Mars – the downward acceleration of electrons supposedly manifesting itself as discrete aurora above Mars. 相似文献