Generation of kinetic Alfvén waves by velocity shear instability on auroral field lines

Ion beams observed in the plasma sheet boundary layer (PSBL), cusp, and on the auroral zone field lines are expected to have spatial gradients in their drift velocity. Generation of kinetic Alfvén waves by velocity shear of the ion beams is discussed. It is shown that a hot ion beam can excite both a resonant kinetic Alfvén wave instability and a non-resonant coupled Alfvén-ion acoustic instability. For typical parameters, observed on the auroral field lines in the altitude range of 5–7 R_E (where R_E is the Earth’s radius), the frequency of the velocity shear modes, in the satellite frame of reference, lie in the ultra-low frequency (ULF) range. The noise due to velocity shear driven Alfvén modes is electromagnetic in nature, and has a finite parallel electric field component.     

The dynamics of the solar radiative zone

The picture of the solar radiative zone is evolving quickly. This review is separated in two parts. We first recall how the two powerful probes of the solar interior, namely the neutrinos and helioseismology have scrutinized the microscopic properties of the solar radiative plasma. Recent observations stimulate today complementary activities beyond the standard stellar model through theoretical modeling of angular momentum transport by rotation, internal waves or (and) by magnetic fields to get access to the dynamical motions of this important region of the Sun. So in the second part, we summarize the first impact of such processes on the radiative zone.     

激波冲击下Air/SF_6斜界面不稳定性实验研究

激波在不同密度介质上的交互作用在可压缩湍流上具有重要的基础价值。激波在界面上的作用会引起Richtmyer-Meshkov不稳定性。激波不正规折射时,流场存在更多复杂的涡。研究马赫数为1.23、1.41的激波在初始倾角β=60°的Air/SF6界面上非正规折射的情况。入射激波的切向冲击和法向冲击的相互作用,在界面处产生涡,折射波在壁面发生马赫反射。利用阴影显示技术,给出了界面演化和混合的过程。     

Electron acoustic solitary waves in the Earth’s magnetotail region

Satellite observations have revealed solitary potential structures in the Earth’s magnetotail region. These structures have both positive (compressive) and negative (rarefactive) electrostatic potentials. In this paper we study the electron-acoustic solitary waves (EASWs) in an unmagnetized plasma consisting of cold plasma electrons and isothermal ions with two different temperatures. Using the reductive perturbation method, the nonlinear evolution of such structures is studied. The numerical computations are performed to study the role of two temperature ions in the generation of EASWs. In this case, the model supports the existence of both positive and negative electrostatic potentials with bipolar pulses. The electric field associated with these positive and negative solitary structures are numerically computed. The present study could be useful to construe the compressive and rarefactive electric field bipolar pulses associated with the BEN type emissions in the magnetospheric regions where the electron beams are not present.     

An explanation of the observation of pulsing hiss at low latitude

In this paper we report pulsing hiss emissions observed at the low latitude station, Jammu (geomag. lat. 22°26′N, L = 1.17) in which intensity decreases with the increase in frequency. The entire dynamic spectra contain somewhat irregular structure. To explain these we propose that the hiss emissions are generated through Doppler-shifted cyclotron interactions near the equator and propagate to the earth in the whistler-mode. Further, ULF waves present in the generation region modulate the intensity of the emission resulting in the pulsing nature. The growth rates are computed and discussed in the light of recent works.     

Cosmic ray anisotropies in the outer heliosphere

The observation of the directional distribution of energetic and cosmic ray particles has been done with the Voyager spacecraft over a long period. Since 2002, when the first flux enhancements of charged particles associated with the approach of Voyager 1 to the solar wind termination shock were observed, these anisotropy measurements have become of special interest. They play an important role to understand the magnetic field and shock structure and the basics of the modulation of cosmic ray and anomalous particles at and beyond the termination shock. They also serve as motivation to study the spatial behavior of galactic and anomalous cosmic ray anisotropies with numerical modulation models in order to illustrate how the radial anisotropy, at different energies, change from upstream to downstream of the termination shock. Observations made by Voyager 1 indicate that the termination shock is a complicated region than previously thought, hence the effects of the latitude dependence of the termination shock’s compression ratio and injection efficiency on the radial anisotropies of galactic and anomalous protons will be illustrated. We find that the magnitude and direction of the radial anisotropy strongly depends on the position in the heliosphere and the energy of particles. The effect of the TS on the radial anisotropy is to abruptly increase its value in the heliosheath especially in the A > 0 cycle for galactic protons and in both polarity cycles for anomalous protons. Furthermore, the global effect of the latitude dependence of the shock’s compression ratio is to increase the radial anisotropy for galactic protons throughout the heliosphere, while when combined with the latitude dependence of the injection efficiency this increase depends on modulation factors for anomalous protons and can even alter the direction of the radial anisotropy.     

A statistical analysis of low frequency geomagnetic field pulsations at two Antarctic geomagnetic observatories in the polar cap region

The aim of this study is to investigate the characteristics of low frequency (∼0.5–5 mHz) geomagnetic field fluctuations as recorded at two Antarctic stations within the polar cap: the Italian observatory Mario Zucchelli Station (TNB) and the French–Italian observatory Dome C (DMC) in order to investigate the spatial extension and propagation characteristics of the phenomena observed at very high latitude. The stations have approximately the same geographic latitude, but a very different corrected geomagnetic latitude, being DMC close to the geomagnetic pole and TNB closer to the auroral oval.     

栅格绕流数值模拟研究

栅格长宽比是影响栅格翼气动特性的重要参数,为研究它对栅格翼气动特性的影响规律,本文通过求解NS方程数值模拟研究单栅格长宽比对栅格气动特性的影响,并且对栅格边框厚度和形状对阻力的影响,在亚、跨、超声速多个马赫数下进行了数值模拟.结果显示,在所选择的长宽比范围内,长宽比对阻力的影响不大,对法向力有明显的影响,选择适当的栅格边框外形和厚度,可以大大减小栅格的阻力.     

ANALYSIS OF THE RETURNED SIGNAL MODEL IN BISTATIC RADAR SYSTEMS

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COMPUTING REACTIVE FLOW ON A COARSE GRID

INTRODUCTIONConsider the Euler equations supplementedby an additional reactive equation which consistsof a scalar balance law for the mass fraction ofunburntgasρρuρEρY t+ρuρu2 + pρu E + upρu Y x=κ000-ρΘ( T) Ywhereρ is the density,ρu the momentum,ρEthe total specific energy,ρY the mass fraction ofunburnt gas( 0≤ Y≤ 1 ) ,κ a large number( thereaction rate) and T temperature.Θ( T) =01 　if T≤ Tignif T>Tign,Tign is the ignition temperature,E=pγ- 1 + u22 + q0 Y,p is …