共查询到17条相似文献，搜索用时 123 毫秒
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根据Grad理论,以麦克斯韦分布函数为基,将离子分布函数展成20矩近似的形式,讨论了黏滞张量项与热流项对离子分布函数的影响.在电场比较弱的情况下,沿着E×B和E的方向上,热流矢量项和黏滞张量项是可以分别忽略掉的.离子温度的各向异性特征和分布函数的不对称性是由黏滞项和热流项引起的.利用Sheffield理论计算得到了非相干散射谱,并对13矩近似和20矩近似得到的非相干散射谱进行了对比.在电场比较弱的情况下,这两种近似基本一致,而当电场增强时,热流张量项的贡献变得很明显,温度各向异性的特征加剧.此时与13矩近似相比较,20矩近似能够更加准确地描述以温度各向异性为特性的非麦克斯韦分布等离子体. 相似文献
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利用美、欧、日等国非相干散射雷达观测的离子速度,高纬地磁站链1 min分辨率H分量及多站地面电离层垂测h'F等多种资料,对高低纬电离层的磁层耦合响应进行事例分析.除常规地磁资料外,极光区两雷达站对F层离子速度的测量是考察高纬电离层对流的很有效手段.本次中强磁暴期间赤道环电流指数Dst的最小值为-136 nT,但其最大的离子速度却超过2500 m/s,双对流圈的西旋则约为30°.从此次事件中极光区两雷达站离子速度的连续观测,得出了物理上合理的电离层对流形态,此图象得到地磁站链记录的有力支持.本事例的中低纬电离层响应再次确认了磁层扰动从高纬向中低纬穿透的事实.此外,Arecibo非相干散射雷达站资料又进一步证明:在同一经度链附近,磁暴期夜间电离层垂测h'F的多站突增现象是东向扰动电场从高纬穿透到中低纬,再通过E×H垂直向上的等离子漂移,使F层底部上升的结果.本文用高、低纬台站的多种观测资料较好地分析了该典型电离层物理现象. 相似文献
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本文介绍了我国曲靖非相干散射雷达的主要技术方案，结合实测数据分析表明该雷达具备了电离层电子密度与等离子体温度观测、空间碎片凝视探测与月球二维成像探测等能力，可用于研究电离层F层气候学特征、电子密度暴时变化与异常增强等天气事件、E-F谷区结构与变化、约3 cm以上尺寸空间碎片的分布特征与模型、月球不同区域的散射回波特性等.下一步将重点开展低电离层与北驼峰结构及演化过程、电离层暴时与扰动特性观测. 相似文献
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极风现象从理论上提出已20多年了,实验上一直没有充分地证实这种现象的存在,以及它的形成区域位于高纬顶部电离层中.我们利用欧洲非相干散射协会（EISCAT）的VHF雷达（在挪威Tromsφ）,对H+离子极风进行了首次实验研究,结果表明,实验期间观测到H+离子在顶部电离层中的运动速度始终向上,且随高度的增加而增大,从而证实在高纬顶部电离层中确实存在着一个永久向上的H+离子流,即H+离子极风,其速度在1000km 高度上达到1km/s,其通量在此高度上接近于饱和,达到1012ms（-1）,而温度小于0.26eV.在我们的探测高度上仍未发展成超声速极风. 相似文献
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In usual incoherent scatter data analysis, the plasma distribution function is assumed to be Maxwellian. In space plasmas, however, distribution functions with a high energy tail which can be well modeled by a generalized Lorentzian distribution function with spectral index kappa (kappa distribution) have been observed. We have theoretically calculated incoherent scatter spectra for a plasma that consists of electrons with kappa distribution function and ions with Maxwellian neglecting the effects of the magnetic field and collisions. The ion line spectra have a double-humped shape similar to those from a Maxwellian plasma. The electron temperatures are underestimated, however, by up to 40% when interpreted assuming Maxwellian distribution. Ion temperatures and electron densities are affected little. Accordingly, actual electron temperatures might be underestimated when an energy input maintaining a high energy tail exists. We have also calculated plasma lines with the kappa distribution function. They are enhanced in total strength, and the peak frequencies appear to be slightly shifted to the transmitter frequency compared to the peak frequencies for a Maxwellian distribution. The damping rate depends on the electron temperature. For lower electron temperatures, plasma lines for electrons with a distribution function are more strongly damped than for a Maxwellian distribution. For higher electron temperatures, however, they have a relatively sharp peak. 相似文献
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以弛豫碰撞模式下Boltzmann方程的解为基础，从极光区视线方向上离子的非Maxwell一维速度分布函数的Raman等人的积分解出发，导出了一维速度分布函数的解析形式解，给出了它的一些特性，并研究了该分布函数随电场增强而出现的饱和现象，给出了物理解释，计算了几种情况下的饱和电场值． 相似文献
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本文讨论了等离子体湍流对电子加速的两种模型:（1）假定在空间中存在一个空间均匀的等离子体湍流区,当具有一定初始分布的电子束通过此湍流区时,研究湍流场对电子束的加速过程;（2）在某一封闭的区域中,存在着具有一定初始分布和空间均匀的等离子体,当某种类型的等离子体波突然传入此等离子体区,然后考察此区中电子的加速过程。在这两种模型中,可能存在着某种电子消失机制。假定湍谱是幂指数形式,我们给出了不同类型湍流扩散系数的普遍形式。利用较简单的数学方法,求解了包括消失过程的一维准线性动力学方程,对于给定的初始分布,得出了分布函数的解析解,并给出了平均能量时间关系的表达式。另外,对于特定的湍谱指数,解出了当平行电场和湍流同时存在时的分布函数。最后,对所得结果进行了数值分析和讨论。 相似文献
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The inversion of incoherent scatter spectra with a non-Maxwellian electron distribution 总被引：1，自引：0，他引：1
Bin Xu Zhange Wang Kun Xue Jian Wu Zhensen Wu Jun Wu Yubo Yan 《Journal of Atmospheric and Solar》2010,72(5-6):492-497
With the action of powerful, high-frequency (HF) radio waves, the ionosphere plasma will depart from the equilibrium state and the non-Maxwellian distribution function can be produced. An artificial field-aligned irregularities (AFAI) model is introduced to describe the distortion from the normal shape, and the measured data are analyzed with this model during ionosphere heating at a 186-km height on August 15th, 2006. The electron temperature and density deduced from the AFAI model are compared with the results obtained from a standard procedure. The inversion of the electron temperature is evidently affected, and the overestimation is up to 22.9%. Owing to the introduction of the AFAI model, the new irregularities’ parameters can be obtained, which implies that incoherent scatter radar is feasible as a ground-based instrument to diagnose information on irregularities. 相似文献
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New results on the information that can be extracted from simulated non-Maxwellian incoherent radar spectra are presented. The cases of a pure ionosphere and of a composite ionosphere typical of a given altitude of the auroral F region are considered. In the case of a pure ionosphere of NO+ or O+ ions it has been shown that the electron temperature and the electron density can be derived from a Maxweilian analysis of radar spectra measured at aspect angles of 0° or 21° respectively; the ion temperature and ion temperature anisotropy can be derived from a non- constraining model such as the ID Raman fitting of a complementary measurement made at an aspect angle larger than 0° for the NO+ ions, or at an aspect angle larger than 21° for the O+ ions. Moreover with such measurements at large aspect angles, the shape of the velocity ion distribution functions can simultaneously be inferred. The case of a composite ionosphere of atomic O+ and molecular NO+ions is a difficult challenge which requires simultaneously a complementary measurement of the electron temperature to provide the ion composition and the electron density from the incoherent radar spectra at a specific aspect angle of 21°; hence, a model dependent routine is necessary to derive the ion temperatures and ion temperature anisotropies. In the case where the electron temperature is not given, a routine which depends on ion distribution models is required first: the better the ion distribution models are, the more accurately derived the plasma parameters will be. In both cases of a composite ionosphere, the 1D Raman fitting can be used to keep a check on the validity of the results provided by the ion distribution model dependent routine. 相似文献
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太阳风的动量涨落将通过磁层边界在磁尾激发磁流体力学波。快磁声波携带扰动能量传到等离子体片中,发展为激波,或者通过激波的相互作用而耗散能量,使等离子体加热。等离子体片中的随机费米加速机制,使麦克斯韦分布尾巴部分的高能量粒子被加速到更高能。在宁静态时,加热、加速与耗散过程平衡。当太阳风的动量或者其涨落较大时,整个加热和加速过程加剧,更多的高能粒子产生,并从等离子体片中逃逸,形成高速的等离子体流注入近地轨道和极区,表现为磁层亚暴过程。利用这种机制,可以解释地球磁层亚暴的定性特征。 相似文献
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In an incoherent scattering radar experiment, the spectral measurement of the so-called up- and downshifted electron plasma lines provides information about their intensity and their Doppler frequency. These two spectral lines correspond, in the backscatter geometry, to two Langmuir waves travelling towards and away from the radar. In the daytime ionosphere, the presence of a small percentage of photoelectrons produced by the solar EUV of the total electron population can excite or damp these Langmuir waves above the thermal equilibrium, resulting in an enhancement of the intensity of the lines above the thermal level. The presence of photo-electrons also modifies the dielectric response function of the plasma from the Maxwellian and thus influences the Doppler frequency of the plasma lines. In this paper, we present a high time-resolution plasma-line data set collected on the EISCAT VHF radar. The analysed data are compared with a model that includes the effect of a suprathermal electron population calculated by a transport code. By comparing the intensity of the analysed plasma lines data to our model, we show that two sharp peaks in the electron suprathermal distribution in the energy range 20–30 eV causes an increased Landau damping around 24.25 eV and 26.25 eV. We have identified these two sharp peaks as the effect of the photoionisation of N2 and O by the intense flux of monochromatic HeII radiation of wavelength 30.378 nm (40.812 eV) created in the chromospheric network and coronal holes. Furthermore, we see that what would have been interpreted as a mean Doppler drift veloCity for a Maxwellian plasma is actually a shift of the Doppler frequency of the plasma lines due to suprathermal electrons. 相似文献