耀斑色球压缩区的传播与谱线的不对称性

色球压缩区是耀斑大气动力学过程的一个基本特征，是产生色球谱线红不对称性的基础，本基于压缩区从大气高层向低层传播的理论公式，在二种不同情况下，计算得到了压缩区内物质运动速度随高度和时间的变化，结果表明，色球蒸发区压力增量△ｐ为常数时压缩区之寿命比压缩区波阵面后压力ｐ２为常数时要长得多，这就大大缓解了以往谱线不对称性的延续时间的理论值比观测值小的矛盾。形成高度不同的谱线具有不同程度的不对称性这一观测     

色球耀斑Hα谱线轮廓不对称性研究

Hα谱线轮廓的不对称性是色球耀斑光谱观测中的重要特征,也是耀斑动力学过程的重要观测事实之一．以紫金山天文台太阳光谱仪的观测资料为依据,给出Hα谱线不对称性的典型轮廓．在考虑氢原子非热激发、电离的作用下,经验性地计算了不同大气模型下谱线的不对称性特征,并在此基础上,对观测谱线进行半经验的研究．结果表明, 色球区的向下运动能够产生Hα谱线的红、蓝不对称性,并可以再生具体耀斑的谱线不对称性特征．此外,不仅非热粒子的能流、谱指数大小以及速度场所处的高度对谱线轮廓有影响,耀斑大气的背景模型对谱线的轮廓也有一定的影响．     

耀斑谱线轮廓不对称性研究

耀斑谱线轮廓的不对称性是耀斑动力学过程的一个重要观测事实。本文在一定的耀斑半经验大气模型基础上,计算了不同速度模式和色球凝聚下的Ha和CaⅡK谱线轮廓,从半经验角度探讨了大气各个层次的速度对Hα和CaⅡK谱线轮廓的影响。结果表明:耀斑早期短时间的Hα蓝不对称性可由位于过渡区的色球凝聚引起;随后的红不对称性是上部色球物质向下运动的结果;而后来出现的CaⅡK不对称性特征则可由色球中、下部具有10—20km/s的向下速度来解释。     

色球耀斑Hα谱线轮廓不对称性研究进展

综述了近年来太阳色球耀斑爆发时Hα谱线不对称性的研究进展,着重讨论了光谱特征和与其对应的不对称性产生机制,以及利用大气半经验模型再生观测谱线轮廓不对称性等方面,并提出尚待解决的主要问题和进一步的研究方向。     

1991年10月24日白光耀斑的高时间分辨率多波段光谱分析

本文分析了南京大学太阳塔1991年10月24日用多波段光谱仪观测到的高时间分辨率（5s）的一个2N／X2．1级白光耀斑光谱．对耀斑谱线轮廓、连续发射强度、X射线和射电爆发资料进行了综合对比，分析表明，该耀斑属Ⅰ类白光耀斑，具有如下特征：（1）在白光耀斑的脉冲相期间，各波段光谱线心强度、连续辐射、谱线半宽以及线翼红不对称性与硬X射线高能波段的爆发同时达到极大；（2）H_a谱线在连续发射极大时半宽达10A，且呈现强烈的线心反转，H_β和H_γ线心亦有反转；（3）所拍摄的5条谱线都有明显的红不对称性，持续时间约为1分钟，根据上述结果，本文用电子束轰击、色球蒸发和色球压缩区对该耀斑能量积聚和释放的动力学机制作了定性的分析和解释。     

太阳大气中氢原子的赖曼谱线

氢是太阳大气中最主要的元素。氢原子的赖曼(Lyman)谱线,尤其是赖曼阿尔法(Ly-α)谱线的辐射,是太阳色球和低过渡区能量损失的主要形式。在太阳的赖曼α像中,网络组织的辐射比较强,而辐射最强的地方是活动区。由于存在辐射转移效应,在宁静区,低阶赖曼谱线的谱形中央一般会形成一个凹陷,而在中央两侧则形成两个峰,两峰往往呈现出一定的不对称性。数值模拟和观测研究表明,赖曼谱线双峰的不对称性与高层大气中各种系统性流动有关。在太阳活动区,赖曼谱形在谱斑区与在宁静区类似;而在黑子区,赖曼谱形几乎没有中央凹陷。赖曼谱形也可用于诊断日珥、耀斑和日冕物质抛射等结构和现象的等离子体特性。该文回顾了赖曼谱线的观测历史,阐明了观测与模拟结果所揭示的物理过程,并结合笔者的认识进行了相应的评论。     

1979年9月19日3B级耀斑光谱分析:金属线的不对称性和线心位移

本文研究了1979年9月19日3B级耀斑金属谱线的不对称性和线心位移.结果表明:强金属线红不对称占主要地位,少数弱金属线也有蓝不对称存在;不对称程度极大发生于线心强度极大之前;不对称性有时可由蓝变红;不管不对称程度如何,线心的位移却很小,总体上仅表现为极微弱的蓝移.文中认为,耀斑爆发时色球压缩区的向下扩展及由此引起的温度极小区上下的物质运动这个动力学过程可基本解释这些观测现象.金属线的研究是对H_α和CaIIK线光谱研究的补充.     

1980年日全食色球闪光光谱观测和初步结果

1980年2月16日日全食时,我们在云南省瑞丽县用一架无缝光谱仪成功地进行了一次闪光光谱观测。仪器由定天镜供光,平均色散度为5.7/mm。光谱底片的高度分辨率为185 km。 观测资料初步分析如下:在4799—5845波段内,证认了1042条色球谱线,其中72条是文献[1]和[2]中未见列出的;确定了色球底的位置;用食既前的太阳边缘的无缝光谱和日食前一天的日心有缝光谱进行了绝对强度定标;测量计算了各条谱线在色球底层附近的强度。 此外,还拍摄到了5303(FeXIV),5445和5694(CaXV)三条日冕线。     

AR5395 1989年3月9日和14日耀斑H_α和CaⅡK线轮廓不对称性的观测

本文利用南京大学太阳塔快速多波段光谱仪观测到的1989年3月9日和14日两个耀斑核块处的光谱资料,分析了Hα和CaⅡK线不对称性随时间的演化。结果得到,3月14日耀斑的Hα和CaⅡK线都有明显的红不对称性,随时间而减弱。由轮廓中分线得到色球物质极大向下运动速度约15～20公里/秒。3月9日耀斑在脉冲相和极大时     

太阳耀斑色球蒸发现象的研究进展

色球蒸发是耀斑能量释放后所导致的一种动力学现象,耀斑发生时,太阳大气被加热,形成的高压驱动等离子体物质向上运动,在观测上表现为高温谱线的多普勒蓝移,有时出现硬X射线足点源逐渐向环顶源的并合过程.数值模拟在理论上验证了色球蒸发理论.色球蒸发的加热机制主要包括热传导和非热粒子束加热.回顾了色球蒸发的研究进展,介绍了不同时期空间仪器对色球蒸发的观测结果,以及数值模拟方面的研究进展,并概括了目前存在的一些主要问题,最后给出简     

On the propagation of chromospheric condensations in solar flares (I)

We simulate dynamically the downward propagation of the chromospheric condensation, which originates following the chromospheric evaporation during solar flares. Our attention is concentrated on the lower part of the atmosphere. The top of the chromosphere (base of the transition region) is regarded as the top boundary. The condensation is mimicked by assuming an impulsive pressure increase at the top boundary. Using such a method, we compute in detail the evolution process of a condensation. The results show that the condensation can penetrate into the deeper atmosphere, though it becomes very weak at the later phase. Moreover, we also discuss the possibility that the mass motions in the condensation may cause the asymmetries of some spectral lines as observations have indicated.     

Spectral analysis of the 3B flare on September 19, 1979: asymmetries and shifts of metallic lines

The asymmetries and Doppler shifts of metallic lines of the 3B flare on September 19, 1979 are investigated in this paper. The results show that: (1) red asymmetries dominate in strong metallic lines, but blue asymmetries also exist in some weak lines; (2) the maximum of the line asymmetry always precedes the maximum of the line intensity; (3) the blue asymmetry occurs generally in the early phase, and can occasionally turn to a red one in the later phase; and (4) the line center has no obvious shift, regardless of the line asymmetry. It is proposed that, the mass motions around the temperature minimum region caused by the impulsive heating or the propagation of the chromospheric condensation can explain these observational results. The study on metallic lines has an auxiliary help for understanding the dynamic process in the lower atmosphere of solar flares.     

On the propagation of chromospheric condensations in solar flares (II)

We study the evolution of the mass motion velocity in the chromospheric condensation, when it propagates into the deeper atmosphere. The condensation is represented by a shock-like structure. Its momentum equation can be solved after some approximations. The computations are carried out for two cases, i.e., the case that the gas pressure just behind the condensation front is constant and the case that the pressure increase at the top of the condensation is constant. The results show that the duration of the condensation in the second case is considerably longer than that in the first case. The most evident difference of the velocity evolution between the two cases appears in their later phase. A comparison of the results in this paper with the dynamic simulations indicates that the second case may be closer to the real situation.     

Are plasma satellites present among chromospheric lines?

From a study of the chromospheric lines listed by Pierce (1968, 1973) indications have been found that first-order plasma satellites appear sometimes as a pair of faint chromospheric emission lines in such places where forbidden lines, mainly of metals, should be located. Second-order satellites are indicated sometimes by an asymmetry in the emission wings of stronger lines, either with respect to intensity or with respect to distance from the line centre and, if so, with the remote wing of diffuse shape. Finally diffuse faint lines, appearing in somewhat greater distances from strong chromospheric lines, suggest the appearance sometimes of fourth-order plasma satellites. All the three types of satellites give electron densities of the order of 10¹² cm^?3. Traces of possible absorption satellites are found also for some of the lines in the solar spectrum. In this connection special attention is drawn to a few faint solar lines located near the wavelengths of corona emission lines. The observational evidence is discussed on the bases of recent theoretical research by Drawin and Truong-Bach (1982a, b).     

Dynamical processes in the June 26, 1999 flare

The evolutionary and spatial characteristics of the motions in the flaring chromosphere of a 2B/M2.3 flare are investigated by analyzing the asymmetry in the H_α profiles. The possibility of reconciling the results of observations with the theory of chromospheric evaporation is considered. The spectroscopic H_α observations of the flare performed with the KG-2 CrAO coronagraph with a temporal resolution of 5–10 s and a spatial resolution as high as 1 arcsec cover all stages of flare development. The following results have been obtained: (1) The H_α profile asymmetry is a general characteristic of the flare emission irrespective of its intensity and its belonging to different structural features and phases of flare development. (2) Most of the H_α emission profiles in flare regions exhibit a red asymmetry. However, a blue asymmetry was observed in small local regions at all stages of flare development. (3) A red asymmetry that appeared before the onset of the impulsive phase and persisted after its end was observed at the sites of main energy release, i.e., the energy source responsible for the dynamical processes in the flare came into operation earlier and existed longer than the HXR emission. (4) The asymmetry pattern changed with flare phase: the red wing intensity dominated in the pre-impulsive phase and at the onset of the impulsive and gradual phases (while the line core was unshifted or slightly shifted). At the maximum of the impulsive phase, the nearly symmetric profiles with extended wings were redshifted as a whole, i.e., the entire emitting volume moved down with a velocity of several tens of km/s. This type of asymmetry cannot be explained by the dynamical model of chromospheric condensation (Canfield and Gayley 1987). (5) The H_α profiles show no evidence of chromospheric heating by a beam of nonthermal electrons during the impulsive phase (Canfield et al. 1984). (6) The lifetime of the downflows and the change in their velocities with time are inconsistent with the dynamical model of chromospheric condensation (Fisher 1989). (7) The morphological features of the velocity field are also inconsistent with the theory of chromospheric evaporation, because the highest differently directed velocities were detected at the flare loop tops, not at the sites of main energy release. We conclude that the investigated flare shows spectral features that are inconsistent with the standard chromospheric evaporation model.     

The Mn <Emphasis Type="SmallCaps">I</Emphasis> 539.47 nm Line Variation in Solar Active Regions

It is a well-established fact that the Mn I 539.47 nm line exhibits significant cycle dependence similar to lines arising in the chromosphere which are affected by non-thermal heating in the chromospheric plages. Among these lines the case of the Mn I 539.47 nm line seems unique. It is of photospheric origin on the basis of theoretical calculations but its cyclic dependence hints at a chromospheric nature. The present work provides further evidence to both connections. The line exhibits asymmetry features and a center-to-limb variation as though influenced by the photospheric granulation. On the other hand an enhancement of the central intensity has been detected in a well identifiable Ca plage area. The line seems to be a promising candidate as an irradiance variation indicator.     

The influence of chromospheric condensation on Hα line profiles

The influence of the chromospheric condensation on H line profiles for the thermal model of a solar flare has been empirically studied in this paper. The so-called thermal model here means that there is no temperature increase relative to the quiet-Sun chromosphere but with a chromospheric condensation in the lower part of its transition region, which case is assumed to represent the early stage of the impulsive phase. The main results include: when the temperature within the condensation region is assumed to be equal to that in front of it, the influence is to create an additional absorption profile overlapping on the original one; by increasing the condensation strength, the H line profile changes from a little line-center increase to broadened red asymmetry, then to the reversed red asymmetry, and finally to two independent absorption profiles; the thickness of the condensation determines the absorption of the additional profile; descending the transition region has no obvious effect on the basic characteristic of the H line profile except a little increase in the line center. Assuming that the temperature within the condensation is higher than that ahead of the condensation, the calculated H line profiles may be strong enough to be comparable with the observations. This means that if the condensation in the purely thermal model can reach a higher temperature, we may also use only thermal origin to explain a chromospheric flare.Alexander von Humboldt Research Fellow, on leave from Purple Mountain Observatory, Nanjing, China.     

A study on the Hα line asymmetry of chromospheric flares

The asymmetry of H_α line profiles is an important characteristic in the spectral observations of chromospheric flares, as well as one of the important observational facts of the dynamical process in solar flares. Based on the observed data of the solar spectrograph of Purple Mountain Observatory, some typical asymmetric H_α line profiles are presented. Taking the effects of the nonthermal excitation and ionization of hydrogen atoms into consideration, the asymmetry characteristics of H_α line profiles under different atmospheric models are calculated, and a semi-empirical study on the observed line profiles is thereby made. The results indicate that the downward motion of the chromospheric condensation region can cause the red and blue asymmetries of H_α spectra. We have tried to reproduce the observed asymmetry characteristics in specific flares. It is found that, besides the energy flux of nonthermal particles, the magnitude of spectral index and the height of the velocity field affect the line profile, the flare's atmospheric background model also has some influence on the line profile.     

Simultaneous Stokes-V diagnostic of a Sunspot using Mg b and Fe I lines

Simultaneous observations of Stokes profiles in photospheric Fei (630.15 nm and 630.25 nm) and chromospheric Mgi b ₁ and b ₂ (518.4 nm and 517.3 nm) lines over a sunspot are presented. Observations were carried out using the Advanced Stokes Polarimeter of HAO/NSO, VTT, SacPeak, U.S.A. The Stokes-V amplitude asymmetries for these lines are analyzed. The values of amplitude asymmetry in Mgb lines are negative in disk-center-side penumbra while they are positive in limb-side penumbra. This trend is similar in nature to photospheric Fei line observations. Further, the spatial distribution of Stokes-V asymmetry is analyzed using Net Circular Polarization (NCP) maps. The chromospheric and photospheric NCP maps are different in many aspects. These observations with longitudinal magnetic field, estimated using weak field approximation, are discussed in this paper.