与耀斑相关的磁场演化

本文利用紫金山天文台太阳光谱仪缝前附属Ｄａｙｓｔａｒ滤光器拍摄的，发生在ＮＯＡＡ５３９５活动区中的三个耀斑的Ｈα单色光资料，对比北京天文台怀柔观测站取得的光球磁场资料，研究耀斑产生位置与光球磁场演化的关系，结果表明：（１）在所研究的５０个耀斑亮核中，有３８个位于新浮磁流区附近，另有少数亮核出现在磁对消区；（２）耀斑亮核多集中在横场方向交叉，剪切角大的复杂磁区，耀斑后多数区域磁场结构简化；（３）耀斑     

AR5395:耀斑触发和磁场演化

利用紫金山天文台太阳光谱仪缝前监视器拍摄到Boulder编号为5395活动区的Hα放大像资料以及北京天文台怀柔观测站提供的活动区磁场资料,我们从两个方面研究了磁场演化与耀斑触发的关系问题。     

AR6659光球色球的磁场速度场的演化特征及其与大耀斑的关系

ＡＲ６６５９是２２周以来最重要的一个活动区，它爆发了２２周最强大的高能事件。本文用云南天文台的光球、色球精细结构照片和北京天文台怀柔站的磁场速度场资料，分析了该活动区磁场速度场的二维位形和大耀斑期间的演化特征。本文分析的４个大耀斑均爆发在中性线附近的Ｎ极区磁场梯度大的地方及色球速度场的红移区。偏带观测也显示耀斑物质是向红端移动的。耀斑波沿横场传播在离本黑子群几万至十几万公里的地方激起感生耀斑，在原生耀斑与感生耀斑之间往往有耀斑环相连。此外，本文还从演化特征出发分析了耀斑爆发前活动区等离子体的宏观不稳定性。     

1989年1月14日AR5312活动区中的耀斑和磁场的关系(英文)

1989年1月14日AR5312(怀柔编号89009)活动区,产生了一个2B级耀斑。该活动区经纬度为L306、S32,黑子群磁场分类为δ型。耀斑开始时间为0202UT,结束为0534UT,持续了3个多小时。北京天文台磁场望远镜,得到了一系列较完整的高分辨磁场及速度场资料,包括光球5324A的矢量磁场图和色球4861A的纵向磁场图(图1、2)。从耀斑前后的磁图得到以下结果: 1、耀斑初始亮点位于纵向磁场中性线附近高度剪切区域(见图1B区)、新浮磁流区(图2D区)以及双极磁结构对消区。前两种区域均能形成电流片,并且引起磁流体不稳定性,从而激发耀斑,但对消区和耀斑的关系不是很清楚,有待于理论工作者进一步探讨。 2、耀斑极大时间过后,光球和色球H_(11)=0线附近纵场梯度均有明显下降。 3、在强剪切区域(图1B区),5324A横向磁场和H_(11)=0线之间的夹角在耀斑极大时间过后有明显增大,该现象表明磁能释放后,磁场剪切缓解。 4、耀斑初始亮点产生后磁场高度剪切区、新浮磁流区和双极对消区,其触发耀斑的作用和周围的磁场环境有密切关系,特别是象具有磁海湾结构这样的活动区,似乎更容易产生耀斑。 5. 该活动区色球磁场位形,较光球磁场位形复杂,主要表现在:色球的纵场出现了一些磁弧岛结构,其原因可能是光球之上的磁力线高度剪切区及扭绞所致。0411     

X级耀斑过程中的磁剪切变化(英文)

通过对活动区NOAA 6891中三个X级耀斑前后的向量磁场分析 ,研究耀斑发生条件与耀斑发生前后横向磁场和磁剪切变化的关系。我们发现与Hagyard的耀斑发生条件不同的是 ,强的横向磁场和磁剪切不是活动区中耀斑发生的充要条件。我们的结果表明 ,活动区NOAA 6891 1 991年 30日的耀斑发生在横向磁场和磁剪切剧烈下降后。尽管 1 0月 2 7日的耀斑发生后横向磁场和磁剪切变化很大 ,但由于有新磁流浮现 ,造成磁中性线的改变 ,使得横向磁场和磁剪切变化与耀斑发生的联系变得比较复杂。     

X线耀斑过程中的磁剪切变化

通过对活动区ＮＯＡＡ６８９１中三个Ｘ线耀斑前后的向量磁场分析,研究耀斑发生条件与耀斑发生前后横向磁场和磁剪切变化的关系。我们发现与Ｈａｇｙａｒｄ的耀斑发生条件不同的是,强的横向磁场和磁剪切不是活动区中耀斑发生的充要条件。我们的结果表明,活动区ＮＯＡＡ６８９１ １９９１年３０日的耀斑发生在横向磁场和磁剪切剧烈下降后。尽管１０月２７日的耀斑发生后横向磁场和磁剪切变化很大,但由于有新磁流浮现,造成磁中性     

AR6659光球色球的磁场速度场的演化特征及其与大耀斑的关系

ＡＲ６６５９是２２周以来最重要的一个活动区，它爆发了２２周最强大的高能事件。本文用云南天文台的光球、色球精细结构照片和北京天文台怀柔站的磁场速度场资料，分析了该活动区磁场速度场的二维位形和大耀斑期间的演化特征，本文分析的４个大耀斑均爆发在中性线附近的Ｎ极区磁场梯度大的地方及色球速度场的红移区，偏带观测也显示耀斑物质是向红端移动的。耀斑波沿横场传播在离本黑子群几万至十几万公里的地方激起感生耀斑，在原     

太阳活动区常α无力场数值计算及其在耀斑预报中的可能应用

本文综述作者及其合作者近年来在太阳活动区无力场数值计算及其应用方面的研究概况。文中简要评价了现有几种太阳活动区常α无力场数值计算表达式,并且叙述了把常α无力场数值计算应用于耀斑研究的结果。得到的主要结论为:(1)现有几种活动区常α无力场数值计算表达式中,Chiu的公式比较好;(2)用Chiu公式外推得到的活动区磁场结构,能够较好地解释观测到的许多现象,表明常α无力场近似仍不失为一种可以接受的活动区磁场模型;(3)活动区无力场的某些参数,如无力因子α和自由磁场能ΔE(定义为无力场能与势场能之差),与耀斑发生率密切相关,可以作为耀斑预报的判据。     

1988年3月黑子磁场的演化(英文)

024黑子(S.G.D编号为4964)是1988年3月份太阳上最大、磁场最强的黑子群。在日面上出现的半个月里,始终有耀斑产生。北京天文台怀柔太阳磁场望远镜对这个活动区作了常规观测,并获得了磁场和速度场资料。 024活动区是由一个偶极黑子和δ黑子组成的。12日01~h49~mUT,黑子刚从东部出现时就有耀斑和活动日珥产生。从速度场与H_β色球单色像对比来看,耀斑内有物质向里流动,而暗条中有物质向外抛射。024活动区的磁场十分复杂,S极、N极磁场互相包含、渗入、剪切,形成许多海湾结构。可能这就是产生了许多各种形状的耀斑的缘故。本文对磁场的形态作了描述。     

高能耀斑指数的功率谱及其热点分布

本文采用一个表征高能耀斑强度的综合指数,分析了太阳活动21周以来(1976.7—1991.2)级别≥M1.0的X射线耀斑和能量≥10Mev的质子耀斑综合指数的时空分布,提出在研究时段内太阳上的13个高能耀斑“热点”。这些热点活动区反复回转,爆发了占总指数58.1％的高能耀斑。本文还讨论了高能耀斑热点的特征及其与大尺度磁场演化的关系。结果表明,高能耀斑热点与大尺度磁场的演化关系密切,前者受后者的调制。     

Variations of magnetic fields and electric currents associated with a solar flare

The high-resolution vector magnetograms obtained with the solar telescope magnetograph of the Beijing Astronomical Observatory of the active region AR 4862 on 7 October, 1987, close before and after a solar flare, were used to calculate the electric current densities in the region. Then the relations between the flare and the magnetic fields as well as the electric currents were studied. The results are: (i) the transverse magnetic fields, and hence the longitudinal electric currents in the region before and after the flare, are evidently different, while the longitudinal magnetic fields remain unchanged; (ii) this confirms the result obtained previously that the flare kernels coincide with the peaks of longitudinal electric density in active regions; (iii) the close relation between the flare kernels and the electric currents indicates that the variations of the transverse magnetic fields and the longitudinal electric currents arise not from the general global evolution of the active region, but from the flare. These results tend to the conclusion that the triggering of a solar flare might be related with the plasma instability caused by the surplus longitudinal electric currents at some local regions in the solar atmosphere.     

An electric-current description of solar flares

The presently prevailing theories of solar flares rely on the hypothetical presence of magnetic flux tubes beneath the photosphere and the two subsequent hypotheses, their emergence above the photosphere and explosive magnetic reconnection, converting magnetic energy carried by the flux tubes to solar flare energy. In this paper, we discuss solar flares from an entirely different point of view, namely in terms of power supply by a dynamo process in the photosphere. By this process, electric currents flowing along the magnetic field lines are generated and the familiar ‘force-free’ fields or the ‘sheared’ magnetic fields are produced. Upward field-aligned currents thus generated are carried by downward streaming electrons; these electrons can excite hydrogen atoms in the chromosphere, causing the optical Hα flares or ‘low temperature flares’. It is thus argued that as the ‘force-free’ fields are being built up for the magnetic energy storage, a flare must already be in progress.     

Prominence motions and their implications for magnetic fields

Using results obtained in our earlier paper (Ballester and Kleczek, 1983) and the equipartition principle we attempt to calculate the lower limits of magnetic fields in three solar prominences. The values are then compared with the magnetic fields found by experimental methods. Furthermore, we have calculated by Ampère's law the lower limits of electric currents inside the conical surface where the knot's motion is located. The results obtained are compared with a few determinations of electric currents in prominences, that can be found in the bibliography. An attempt is made to use a three-currents system to explain the configuration of magnetic fields in solar prominences.     

Magnetospheric tail dynamics and a concept of combined action of viscous drag and magnetic merging

Characteristic features of the two solar wind-magnetosphere interaction mechanisms, i.e. the viscous drag and magnetic merging, are discussed in the paper. The main difference between them is that the viscous drag acts mainly near the equatorial cross-section of the magnetopause, whereas the magnetic merging acts near the noon-midnight meridian cross-section. Energy input to the tail due to viscous drag action decreases as the magnetic flux in the tail lobes increases, whereas the energy input due to magnetic merging does not depend on the magnetotail flux. A concept is developed that a combined action of these two mechanisms is intimately related to substorm occurrence. In this paper large scale cross-tail electric fields and their relation to energy conversion processes in the tail are analysed qualitatively and interpreted. An induced part of the tail electric fields is taken into account and the relationship between polar cap electric fields and energy conversions in the tail is discussed.     

太阳活动区纵向电流密度的计算

本文利用太阳活动区光球横向磁场观测资料推算纵向电流密度分布,论述了具体的计算方法和取得的结果,并简要讨论了太阳活动区电流计算在太阳物理研究中的应用。     

Electric fields in the solar atmosphere

The gross-structure of the force-free currents in the solar atmosphere and their possible dynamics have been discussed as caused by quasi short-circuited electric fields, generated by the motion of the solar magnetic features.     

On the magnetic reconnection of electric currents in solar flares

The role of the electric currents distributed over the volume of an active region on the Sun is considered from the standpoint of solar flare physics. We suggest including the electric currents in a topological model of the magnetic field in an active region. Typical values of the mutual inductance and the interaction energy of the coronal electric currents flowing along magnetic loops have been estimated for the M7/1N flare on April 27, 2006. We show that if these currents actually make a significant contribution to the flare energetics, then they must manifest themselves in the photosphericmagnetic fields. Depending on their orientation, the distributed currents can both help and hinder reconnection in the current layer at the separator during the flare. Asymmetric reconnection of the currents is accompanied by their interruption and an inductive change in energy. The reconnection of currents in flares differs significantly from the ordinary coalescence instability of magnetic islands in current layers. Highly accurate measurements of the magnetic fields in active regions are needed for a quantitative analysis of the role of distributed currents in solar flares.     

Force-free magnetic fields in the solar atmosphere

Reliable measurements of the solar magnetic field are restricted to the level of the photosphere. For about half a century attempts have been made to calculate the field in the layers above the photosphere, i.e. in the chromosphere and in the corona, from the measured photospheric field. The procedure is known as magnetic field extrapolation. In the superphotospheric parts of active regions the magnetic field is approximately force-free, i.e. electric currents are aligned with the magnetic field. The practical application to solar active regions has been largely confined to constant-α or linear force-free fields, with a spatially constant ratio, α, between the electric current and the magnetic field. We review results obtained from extrapolations with constant-α force-free fields, in particular on magnetic topologies favourable for flares and on magnetic and current helicities. Presently, different methods are being developed to calculate non-constant-α or nonlinear force-free fields from photospheric vector magnetograms. We also briefly discuss these methods and present a comparison of a linear and a nonlinear force-free magnetic field extrapolation applied to the same photospheric boundary data. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

An essay on sunspots and solar flares

The presently prevailing theories of sunspots and solar flares rely on the hypothetical presence of magnetic flux tubes beneath the photosphere and the two subsequent hypotheses, their emergence above the photosphere and explosive magnetic reconnection, converting magnetic energy carried by the flux tubes for solar flare energy.In this paper, we pay attention to the fact that there are large-scale magnetic fields which divide the photosphere into positive and negative (line-of-sight) polarity regions and that they are likely to be more fundamental than sunspot fields, as emphasized most recently by McIntosh (1981). A new phenomenological model of the sunspot pair formation is then constructed by considering an amplification process of these largescale fields near their boundaries by shear flows, including localized vortex motions. The amplification results from a dynamo process associated with such vortex flows and the associated convergence flow in the largescale fields.This dynamo process generates also some of the familiar “force-free” fields or the “sheared” magnetic fields in which the magnetic field-aligned currents are essential. Upward field-aligned currents generated by the dynamo process are carried by downward streaming electrons which are expected to be accelerated by an electric potential structure; a similar structure is responsible for accelerating auroral electrons in the magnetosphere. Depending on the magnetic field configuration and the shear flows, the current-carrying electrons precipitate into different geometrical patterns, causing circular flares, umbral flares, two-ribbon flares, etc. Thus, it is suggested that “low temperature flares” are directly driven by the photospheric dynamo process.     

Electron Acceleration in Reconnecting Current Sheets

We present the results of charged particle orbit calculations in prescribed electric and magnetic fields motivated by magnetic reconnection models. Due to the presence of a strong guide field, the particle orbits can be calculated in the guiding centre approximation. The electromagnetic fields are chosen to resemble a reconnecting magnetic current sheet with a localised reconnection region. An initially Maxwellian distribution function in the inflow region can develop a beam-like component in the outflow region. Possible implications of these findings for acceleration scenarios in solar flares will be discussed.