Electromagnetic Ion Beam Instability in the Solar Corona

Remote-sensing measurements indicate that heavy ions in the corona undergo an anisotropic and mass-charge dependent energization.A popular explanation to this phenomenon is the damping of the Alfven/ion cyclotron waves.In this paper,we propose that the ion beam instability can be an important source of the Alfven/ion cyclotron waves, and we study the excitation of the ion beam instability in the corona at the heliocentric distance～3R_⊙ and the corresponding energy transfer process ther...     

Plasma-maser Effects in Dusty Plasma

The Plasma-maser instablility of Langmuir wave or Em wave in multicom-ponent plasma with stationary charged particulates is considered.The up-conversion of the wave evergy from low-frequency waves to the high-frequency waves is much enhanced owing to the deeper energy exchange between resonant waves and particles in dusty plasma.This results should be useful to interpret the anomalous high-frequency radiation phenomena in laboratory and astrophysical dusty plasma.     

Resonant Heating of Ions by Parallel Propagating Alfvén Waves in Solar Coronal Holes

Resonant heating of H, O+5, and Mg+9 by parallel propagating ion cyclotron Alfven waves in solar coronal holes at a heliocentric distance is studied using the heating rate derived from the quasilinear theory. It is shown that the particle-AlfVen-wave interaction is a significant microscopic process. The temperatures of the ions are rapidly increased up to the observed order in only microseconds, which implies that simply inserting the quasilinear heating rate into the fluid/MHD energy equation to calculate the radial dependence of ion temperatures may cause errors as the time scales do not match. Different species ions are heated by Alfven waves with a power law spectrum in approximately a mass order. To heat O+5 over Mg+9 as measured by the Ultraviolet Coronagraph Spectrometer (UVCS) in the solar coronal hole at a region ≥1.9.R, the energy density of Alfven waves with a frequency close to the O+5-cyclotron frequency must be at least double of that at the Mg+9-cyclotron frequency. With an appropriate wa     

Effects of displacement current on wave dispersion relation and polarization properties in auroral plasmas

In-situ observations from the FREJA magnetospheric research satellite and the Fast Auroral SnapshoT satellite have shown that plasma waves are frequently observed in the auroral plasma,which are believed to be fundamentally important in wave energy dissipation and particle energization.However,the effects of a displacement current on these waves have not been examined.Based on the two-fluid theory,we investigate the dispersion relation and polarization properties of fast,Alfven,and slow modes in the presence of a displacement current,and the effects of the displacement current on these waves are also considered.The results show that the wave frequency,polarization,magnetic helicity and other properties for the fast and Alfven modes are highly sensitive to the normalized Alfven velocity v_A/c,plasma betaβ,and propagation angle θ,while for the slow mode the dependence is minor.In particular,for both fast and Alfven modes,the magnetic helicity is obviously different with and without the displacement current,especially for the Alfven mode with the helicity reversals from right-handed to left-handed when v_A/c increases from 0 to 0.3.The charge-neutral condition of both fast and Alfven modes with frequencies larger than the proton cyclotron frequency is invalid in the presence of the displacement current.Moreover,the presence of the displacement current leads to relatively large magnetic compressibility for the Alfven mode and relatively large electron compressibility for the fast mode.These results can be useful for a comprehensive understanding of the wave properties and the physics of particle energization phenomena in auroral plasmas.     

日冕和行星际空间辐射机制

In this paper, the new models of the generation mechanism of the observed solar corona type II radio burst and the interplanetary type III radio emission are presented. The synchrotron-maser theory of type II solar is proposed. The electrostatic waves with frequencies close to twice the plasma frequency can be excited,and can naturclly change into electromagnetic waves when they propagate in a plasma in which the plasma density decreases spatially.Emission of electromagnetic waves with frequencies close to the plasma frequency and/or its second harmonic have been frequently observed in solar corona and interplanetary space. In the pass a number of theories have been suggested to explain the generation mechanism of the observed radiation.     

The Modulations of the Electromagnetic Waves near 1/2ω_cH~ in Observations of Freja

In this paper the non-linear parametric resonance is proposed to understand the reason why the observed the electromagnetic ion cyclotron waves in the auroral energization region are usually concentrate in the range close to the half value of the proton gyrofrequency [Gustafsson et at.,1990].The electromagnetic ion cyclotron waves are supposed to exist already at ωcH ,then,the non-linear parametric resonane can predict the peak at 1/2ωc H The parametric resonance is saturated by the non-linear effects and a drift of the resonance frequency is also predicted from     

Damping and power spectra of quasi-periodic intensity disturbances above a solar polar coronal hole

We study intensity disturbances above a solar polar coronal hole that can be seen in the AIA 171 A?and 193 passbands,aiming to provide more insights into their physical nature.The damping and power spectra of the intensity disturbances with frequencies from 0.07 m Hz to 10.5 m Hz are investigated.The damping of the intensity disturbances tends to be stronger at lower frequencies,and their damping behavior below 980′′(for comparison,the limb is at 945′′) is different from what happens above.No significant difference is found between the damping of the intensity disturbances in the AIA 171 and that in the AIA193 A?.The indices of the power spectra of the intensity disturbances are found to be slightly smaller in the AIA 171 than in the AIA 193 A?,but the difference is within one standard deviation.An additional enhanced component is present in the power spectra in a period range of 8–40 min at lower heights.The power spectra of a spicule is highly correlated with its associated intensity disturbance,which suggests that the power spectra of the intensity disturbances might be a mixture of spicules and wave activities.We suggest that each intensity disturbance in the polar coronal hole is possibly a series of independent slow magnetoacoustic waves triggered by spicular activities.     

Solar Impulsive Hard X-Ray Emission and Two-Stage Electron Acceleration

Heating and acceleration of electrons in solar impulsive hard X-ray (HXR) flares are studied according to the two-stage acceleration model developed by Zhang for solar 3He-rich events. It is shown that electrostatic H-cyclotron waves can be excited at a parallel phase velocity less than about the electron thermal velocity and thus can significantly heat the electrons (up to 40 MK) through Landau resonance. The preheated electrons with velocities above a threshold are further accelerated to high energies in the flare-acceleration process. The flare-produced electron spectrum is obtained and shown to be thermal at low energies and power law at high energies. In the non-thermal energy range, the spectrum can be double power law if the spectral power index is energy dependent or related. The electron energy spectrum obtained by this study agrees quantitatively with the result derived from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) HXR observations in the flare of 2002 July 23. The total flux and energy flux of electrons accelerated in the solar flare also agree with the measurements.     

WAVELET ANALYSIS IN THE TIME-FREQUENCY SPECTRUM FOR SOME NONLINEAR WAVES OBSERVED BY FREJA SATELLITE

Some new nonlinear plasma waves at the local ion gyrofrequencies or low-hybrid frequency observed by Freja satellite in low aurora( 1700km) are reported and analyzed with the wavelet transformation in the time-frequency spectrum, especially, the multi-frequency structures and their time evolution. Hence, the wavelet transformation may be a powerful method to study the time-frequency fine structures.     

Observation of Small-amplitude Electromagnetic Cyclotron Waves in the Solar Wind

Our previous studies on low-frequency electromagnetic cyclotron waves(ECWs) with amplitudes larger than 0.1nT in the solar wind revealed that the left-handed(LH) polarized ECWs are the dominant waves,and these waves preferentially occur in plasma conditions of high proton speed(V_p),high proton temperature(T_p),low proton density(N_p).In the present study,using magnetic field and plasma data from the Wind mission between 2005 and2015,we perform a survey of small-amp...     

差分法周跳探测与修复方法改进

在目前常用的周跳探测与修复方法基础上 ,提出了首先将观测资料按照观测历元不连续分成若干小弧段 ,然后利用差分法进行周跳探测 ,根据差分后周跳放大的特性判断周跳和野值 ,并确定其位置利用宽带组合和电离层组合的方法解算周跳大小。通过实例验证了其有效性。     

CHARGING OF DUST GRAINS IN COMETARY PLASMA ENVIRONMENTS

The equilibrium potential of fluffy dust grains in plasma environments is modeled numerically for comet P/Halley. It is found that the dust grain acquires its largest negative potential and probability of disruption at about 50, 000km from the comet where the mass spectrum measured by the spacecraft took a great change.     

1.56m望远镜新CCD相机MPP模式开与关的对比(英文)

1 .5 6m望远镜新CCD系统是在里克天文台用其控制电路组装而成的。该系统能在MPP模式与非MPP模式之间自由快速转换。我们比较了两种模式的性能差异 ,得到 :(1)增益和读出噪音不变。 (2 )在 - 10 0℃温度 ,MPP模式的暗流对短的或中等长度的露光可以忽略 ,并且暗流对CCD芯片的温度变化不太敏感 ;非MPP模式的暗流有确定的图案 ,对CCD的温度变化比MPP敏感。因此稳定的低温是必须的 ,并且使用时须减暗流。 (3)使用MPP的代价是 ,相对于非MPP模式 ,动态范围至少减小约 90 0 0adu(增益 4 .6e- /adu)。用户使用时应按照科学目的选择模式。     

Measuring the Fundamental Parameters of Hot Hydrogen－Rich White Dwarfs

This review considers the observations of hot, hydrogen-rich white dwarf stars, with particular reference to measurements of temperature, surface gravity and composition. Spectroscopic data from a variety of wavelength ranges are required for this work and, in particular, the important contributions from optical, ultraviolet and extreme ultraviolet studies are discussed. Using the values of Tefr and log g determined for an individual white dwarf, estimates of mass and radius might be derived from the theoretical mass-radius relation. The issue of the accuracy of the theoretical mass-radius calculations and the prospects for making empirical tests using observational data are outlined.     

小波分析理论在GPS技术中的应用

在GPS数据处理中 ,存在着误差影响、影响波的干扰、周跳和数据量大等问题。误差影响和影响波的干扰实质是在接收卫星信号时受到其它因素的影响 ;周跳是由于卫星信号的失锁而造成信号的不连续 ;数据量大是因为GPS观测需要采样间隔小又连续观测所致。由于小波理论具有时频分析、波形分解、特征提取和快速小波变换等特性 ,应用小波变换和波形分解可以解决误差影响和影响波的干扰的问题 ;应用特征提取可以解决周跳检测问题 ;应用快速小波变换可进行数据压缩     

A Study on the Technique of Observing Interplanetary Scintillation with Simultaneous Dual-Frequency Measurements

Ground-based observation of Interplanetary Scintillation(IPS)is an important ap- proach of monitoring solar wind speed.We describe both the principle and method of ob- serving the solar wind speed by using the normalized cross-spectrum of simultaneous dual- frequency IPS measurement.The effects of the solar wind properties and the angular size of the scintillation source on the measurement of solar wind speed are investigated by numerical analysis.We carry out a comparison of this method with the traditional single station-single frequency method.We outline a new IPS observation system using this method now under construction at the National Astronomical Observatories,CAS(NAOC).     

Measuring the Fundamental Parameters of Hot Hydrogen- Rich White Dwarfs

This review considers the observations of hot, hydrogen-rich white dwarf stars, with particular reference to measurements of temperature, surface gravity and composition. Spectroscopic data from a variety of wavelength ranges are required for this work and, in particular, the important contributions from optical, ultraviolet and extreme ultraviolet studies are discussed. Using the values of Teff and log g determined for an individual white dwarf, estimates of mass and radius might be derived from the theoretical mass-radius relation. The issue of the accuracy of the theoretical mass-radius calculations and the prospects for making empirical tests using observational data are outlined.     

球状星团M79天区169颗恒星的位置和自行归算及其成员概率

使用上海天文台佘山40cm折射望远镜拍摄的底片资料,对球状星团M79中心附近15’×15’天区内106颗恒星和63颗Tycho-2星,以《Tycho-2星表》中M79附近1°×1°天区内上述63颗Ty cho-2星的位置和自行为参考,归算得到了所有169颗恒星的位置和自行,并估计了其成员概率。     

疏散星团NGC6530天区的恒星自行和成员概率

利用上海天文台的照相底片资料,确定了疏散星团NGC6530天区364颗恒星的自行和成员概率,并对有关自行测定的方法、结果和精度等问题作了较为详细的介绍和讨论。使用的底片历元差为87年,全部恒星自行中误差的均方根值为1．09mas/a。