共查询到18条相似文献，搜索用时 156 毫秒
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正电磁离子回旋波是指频率低于或者接近离子回旋频率的电磁波,其存在左旋和右旋两种偏振状态.通过回旋共振相互作用,电磁离子回旋波能直接与粒子发生能量交换,对太阳风等离子体加热和加速等能化现象起着重要作用.然而,太阳风中电磁离子回旋波的激发机制及其波粒相互作用尚未完全清楚.本学位论文深入、系统地研究了太阳风等离子体环境下离子束流对电磁离子回旋波激发机制的影响及其波粒相互作用,为进一步理解与解释太阳风中微观等离子体物理过程、 相似文献
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由磁绳结构主导、平均尺度约二、三十个小时的行星际磁云是日冕物质抛射在行星际膨胀、传播的体现。最近，Moldwin等人报道在太阳风中还观测到一些尺度在几十分钟的小尺度磁绳结构，并认为太阳风中的磁绳结构在尺度分布上可能具有双峰特征，在全面检视了WIND卫星(1995年-2000年)和ACE卫星(1998年-2000年)的观测资料后，发现了在行星际太阳风中一些尺度为几个小时的中尺度磁绳结构，利用初步整理的其中28个中尺度磁绳结构事件，认为太阳风中的磁绳结构在尺度分布上可能是连续的，这对行星际太阳风中磁绳结构物理起源的研究可能提出重要的物理限制。 相似文献
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电子是太阳风粒子中最为重要的组分之一,它可以通过多种机制对太阳风产生影响.太阳风中的电子通常具有温度各向异性和束流两种非热平衡分布特征,这些偏离热平衡分布的特征可以通过波粒相互作用激发电子不稳定性和等离子体波动,激发的等离子体波动又可以通过波粒相互作用调制太阳风粒子的分布,从而加热太阳风中的背景粒子.因此电子动力学不稳定性在太阳风的演化过程中扮演了极为重要的角色.详细介绍了太阳风中常见的电子动力学不稳定性,并基于等离子体动力论,详细介绍太阳风传播过程中所出现的各种不稳定性,尤其是在近日球层和太阳大气区域所出现的电子声热流不稳定性以及低混杂热流不稳定性,并分析其波粒相互作用机制,以便更加深入地研究太阳风传播过程中的电子分布函数演化. 相似文献
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概述了１９８８年１２月１６日出现在微波Ⅳ型大爆发上的快变分量观测特征，以及由ＭＨＤ调制磁流管的磁场强度，而产生了１２．５ｍｉｎ和１．２ｍｉｎ的长短准周期振荡。一部分高能电子被磁场俘获，做同步加速回旋辐射，产生了微波Ⅳ型爆发。另一部分高能电子以一定入射角喷注在磁拱上，形成螺距角各为异性的空心束分布，其电子回旋不稳定性导致ｓｐｉｋｅ辐射。最后，用慢波模式计算了三个频率上的１．２ｍｉｎ的准周期振荡，结果表明振荡周期随频率的增加而增大，与观测结果相符。 相似文献
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概述了１９８８年１２月１６日出现在微波Ⅳ型大爆发上的快变分量观测特征，以及由ＭＨＤ调制磁流管的磁场强度，而产生了１２．５ｍｉｎ和１．２ｍｉｎ的长短准周期振荡，呈部分高能电子被磁场俘获，做同步加速回旋辐射，产生了微波Ⅳ型爆发，另一部分能电子以一定入射角喷注磁拱上，形成螺距角各为异性的空心束分布，其电子回旋不稳定性导致ｓｐｉｋｅ辐射。最后，用慢波模式计算了三个频率上的１．２ｍｉｎ的准周期振荡，结果表明 相似文献
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空间飞船Hellos 1和2的观测表明由0.3AU至0.9gAU,Alfven脉动振幅的衰减比Alfven波传播的WKB解预计的振幅变化要大.Alfven脉动能谱密度的变化可以表示为WKB解预计的能量变化乘以一个衰减因子e~(-2(r-r_0))/λ(f),其中r=0.87AU,r_0=0.29AU,λ(f)称为耗散长度.当频率f>10~(-2)Hz时,λ近似为一常数,λ的变化主要发生在低频区.这一现象对有关Alfven脉动耗散的理论提出了一个新的检验标准。本文导出了与Alfven脉动的波能串级模式和粘性衰减模式相应的耗散长度的解析表达式,并将Helios观测得到的太阳风参数代入进行计算.通过计算结果与实际观测的比较发现,波能串级模式给出的耗散长度的数值及其随频率变化的趋势与实际观测结果一致,而粘性模式给出的结果与实际相差很大. 相似文献
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磁云因其独特的磁场结构经常是重大灾害性空间天气的驱动源.近来从磁云的边界层结构、环向通量、大尺度结构等方面关于磁云传播的动力学演化过程的研究取得了一些进展.在磁云边界存在一个由于磁场重联而形成的边界层结构.在磁云传播过程中,这种发生在边界处的磁场重联可能会把磁云的磁场剥蚀掉,进而引起其磁通量绳结构环向通量的减少以及不对称.在磁云内部,经常会观测到多个子通量绳结构.这些特性各异的子通量绳可以通过磁场重联而合并,进而引起磁云磁结构的改变.关于磁云大尺度磁场拓扑位形的演化机制,除了较早提出的交换重联外,目前的研究表明在行星际空间中,磁云边界处的重联过程也可以将磁云闭合或半开放的磁场线打开或断开.尽管在相关研究中已经取得了较大进展,但关于磁云传播的动力学演化过程还有许多问题尚不清楚.在行星际小尺度磁通量绳边界也发现了边界层结构,那么磁云是否会因剥蚀而成为小尺度通量绳?磁云内子通量绳结构在相互作用中会不会引起某些不稳定性而导致整个通量绳系统的崩溃?这些问题的解决还有待于进一步的理论、观测和数值模拟研究. 相似文献
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Y. Q. Hu 《Astrophysics and Space Science》1996,235(1):141-147
This review briefly surveys some recent progress in the numerical simulation study of magnetohydrodynamic (MHD) shock waves in the solar wind. 相似文献
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Encounter of Voyager with Saturn’s environment revealed the presence of electromagnetic ion-cyclotron waves (EMIC) in Saturnian magnetosphere. Cassini provided the evidence of dynamic particle injections in inner magnetosphere of Saturn. Also inner magnetosphere of Saturn has highest rotational flow shear as compared to any other planet in our solar system. Hence during these injections, electrons and ions are transported to regions of stronger magnetic field, thus gaining energy. The dynamics of the inner magnetosphere of Saturn are governed by wave-particle interaction. In present paper we have investigated those EMIC waves pertaining in background plasma which propagates obliquely with respect to the magnetic field of Saturn. Applying kinetic approach, the expression for dispersion relation and growth rate has been derived. Magnetic field model has been used to incorporate magnetic field strength at different latitudes for radial distance of \(6.18~R_{{s}}\) (\(1~R_{{s}}= 60{,}268~\mbox{km}\)). Various parameters affecting the growth of EMIC waves in cold bi-Maxwellian background and after the hot injections has been studied. Parametric analysis inferred that after hot injections, growth rate of EMIC waves increases till \(10^{\circ}\) and decreases eventually with increase in latitude due to ion density distribution in near-equatorial region. Also, growth rate of EMIC waves increases with increasing value of temperature anisotropy and AC frequency, but the growth rate decreases as the angle of propagation with respect to \(B_{0}\) (Magnetic field at equator) increases. The injection events which assume the Loss-cone distribution of particles, affect the lower wave numbers of the spectra. 相似文献
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Stephen Pintér 《Solar physics》1974,35(1):225-232
The annual average values of the solar wind velocity over the period 1962–1972 were investigated on the basis of data obtained from different space probes. The comparison of the pattern of the annual average solar wind velocities observed by the Vela and Pioneer 6 satellites indicates that the pattern presented by Gosling et al. (1971) is realistic. The long-range trend in the solar wind velocity during the 11-year cycle is governed by the number and intensity of irregularities occurring in the corona. These irregularities may represent motions of mass or some types of MHD shock waves and they are responsible for the increased heating of the corona which then in turn causes an increase in the values of the solar radar cross-section and of the solar wind velocity. A close relation is demonstrated between the monthly and annual average values of the solar wind velocity and of the cross-section. 相似文献
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Arne K. Richter 《Astrophysics and Space Science》1975,36(2):383-405
Applying an Alfvén-Wave-Extended-QRH-approximation and the method of characteristics, we solve the equations of motion for outwardly propagating Alfvén waves analytically for three different cases of an azimuthal dependence of the background solar wind, (a) for a pure fast-slow stream configuration, (b) for the situation where the high-speed stream originates from a diverging magnetic field region, and (c) for the case of (b) and an initially decreasing density configuration (‘coronal hole’). The reaction of these waves on the background state as well as mode-mode coupling effects are neglected. These three solar wind models are discussed shortly. For the superimposed Alfvén waves we find, on an average, that there is a strong azimuthal dependence of all relevant wave parameters which, correlated with the azimuthal distributions of the solar wind variables, leads to good agreements with observations. The signature of high-speed streams and these correlations could clearly indicate solar wind streams originating from ‘coronal holes’. Contrary to the purely radial dependent solar wind, where outwardly propagating Alfvén waves are exclusively refracted towards the radial direction, we now find a refraction nearly perpendicular to the direction of the interplanetary magnetic field in the compression region and closely towards the magnetic field direction down the trailing edge and in the low-speed regime. 相似文献
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Ion cyclotron waves are generated in the solar wind when it picks up freshly ionized planetary exospheric ions. These waves grow from the free energy of the highly anisotropic distribution of fresh pickup ions, and are observed in the spacecraft frame with left-handed polarization and a wave frequency near the ion’s gyrofrequency. At Mars and Venus and in the Earth’s polar cusp, the solar wind directly interacts with the planetary exospheres. Ion cyclotron waves with many similar properties are observed in these diverse plasma environments. The ion cyclotron waves at Mars indicate its hydrogen exosphere to be extensive and asymmetric in the direction of the interplanetary electric field. The production of fast neutrals plays an important role in forming an extended exosphere in the shape and size observed. At Venus, the region of exospheric proton cyclotron wave production may be restricted to the magnetosheath. The waves observed in the solar wind at Venus appear to be largely produced by the solar-wind-Venus interaction, with some waves at higher frequencies formed near the Sun and carried outward by the solar wind to Venus. These waves have some similarity to the expected properties of exospherically produced proton pickup waves but are characterized by magnetic connection to the bow shock or by a lack of correlation with local solar wind properties respectively. Any confusion of solar derived waves with exospherically derived ion pickup waves is not an issue at Mars because the solar-produced waves are generally at much higher frequencies than the local pickup waves and the solar waves should be mostly absorbed when convected to Mars distance as the proton cyclotron frequency in the plasma frame approaches the frequency of the solar-produced waves. In the Earth’s polar cusp, the wave properties of ion cyclotron waves are quite variable. Spatial gradients in the magnetic field may cause this variation as the background field changes between the regions in which the fast neutrals are produced and where they are re-ionized and picked up. While these waves were discovered early in the magnetospheric exploration, their generation was not understood until after we had observed similar waves in the exospheres of Mars and Venus. 相似文献
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M. Dryer S. T. Wu G. Gislason S. M. Han Z. K. Smith J. F. Wang D. F. Smart M. A. Shea 《Astrophysics and Space Science》1984,105(1):187-208
A time-dependent, nonplanar, two-dimensional magnetohydrodynamic computer model is used to simulate a series, separately examined, of solar flare-generated shock waves and their subsequent disturbances in interplanetary space between the Sun and the Earth's magnetosphere. The ‘canonical’ or ansatz series of shock waves include initial velocities near the Sun over the range 500 to 3500 km s?1. The ambient solar wind, through which they propagate, is taken to be a steady-state homogeneous plasma (that is, independent of heliolongitude) with a representative set of plasma and magnetic field parameters. Complete sets of solar wind plasma and magnetic field parameters are presented and discussed. Particular attention is addressed to the MHD model's ability to address fundamental operational questions vis-à-vis the long-range forecasting of geomagnetic disturbances. These questions are: (i) will a disturbance (such as the present canonical series of solar flare shock waves) produce a magnetospheric and ionospheric disturbance, and, if so, (ii) when will it start, (iii) how severe will it be, and (iv) how long will it last? The model's output is used to compute various solar wind indices of current interest as a demonstration of the model's potential for providing ‘answers’ to these questions. 相似文献
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The energization of positive ions in front of a cometary bow shock is investigated. Ions produced by ionization of the cometary neutrals interact with the solar wind protons to produce, among other waves, large amplitude oscillations of the ambient magnetic field. Such oscillations are convected towards the comet at the unperturbed solar wind speed far from the shock and at a lower speed closer to the shock (due to the solar wind mass loading) ; hence, they can energize the suprathermal ions by Fermi acceleration. The spatial extension of the acceleration region is of the order of 106 km and the resulting ion energy spectrum is harder than in the Earth's bow shock case. The energization of cometary ions produces an additional deceleration of the solar wind, such that the cometary bow shock of Halley-type comet may be regarded as a “cosmic ray shock”. 相似文献