太阳磁场观测研究

简要回顾了近几年国际上太阳磁场研究的一些重要进展，包括耀斑与磁切和电流的关系，电流螺度和磁螺度，磁场拓扑性，三维磁场外推，色球磁场研究，日冕磁场研究，内网络磁元，磁流和振荡，极区磁场观测以及色球磁元观测等方面内容，同时也介绍了怀柔太阳观测站最近所取得的主要成果，自20世纪90年代以来，YOHKOH高分辨率的太阳X射线数据，SOHO的多波段大尺度观测，TRACE的高分辨太阳过渡区资料，为研究太阳磁场从内部到距离几十太阳半径处的大范围演化提供了依据，高效的空间资料结合长期的地面资料，将是正派推动太阳磁场研究的重要手段和必然趋势。     

磁对消引起的日珥扰动

采用二维三分量理想磁流体力学模型,研究光球磁对消引起的日珥扰动．日珥下方光球表面的磁对消将磁通量向日珥传输,引起日珥内部磁通量和磁螺度增加．日珥的状态与所积累的磁通量（或磁螺度）有关．数值结果显示,如果日珥磁通的相对增量δＦ（或相应的磁螺度相对增量δＨ）较小,日珥只略微上升和膨胀,并不离开光球;而对于较大的δＦ或δＨ）;日珥将脱离光球,悬浮在低层日冕中,在其下方形成垂直电流片．     

太阳光球磁场的螺度

本文首先给出了近两年来我们在太阳活动区光球电流螺度的观测与研究中所取得的一些最新结果。其次,我们也展望了太阳第２３ 周峰年期间有关磁螺度研究的若干课题     

日冕三重无力场电流片的磁场重联

采用二维三分量磁流体力学模型,对日冕三重无力场电流片的磁场重磁联进行了数值研究,揭示了重联过程的基本物理特征,这类重联过程将加热和加速日冕等离子体,并导致多个高温、高密度、高磁螺度的磁岛的形成和向上喷发,这表明,多重无力场电流片的重联可能在日冕磁能释放、上行等离子体的形成和太阳磁场螺度向行星际空间的逃逸方面起重要的作用。     

日冕三重无力场电流片的磁场重联

采用二维三分量磁流体力学模型,对日冕三重无力场电流片的磁场重联进行了数值研究,揭示了重联过程的基本物理特征．这类重联过程将加热和加速日冕等离子体,并导致多个高温、高密度、高磁螺度的磁岛的形成和向上喷发．这表明,多重无力场电流片的重联可能在日冕磁能释放、上行等离子体团的形成和太阳磁场螺度向行星际空间的逃逸方面起重要的作用．     

磁对消引起的日珥扰动

采用二维三分量理想磁流体力学模型,研究光球磁对消引起的日珥扰动。日珥下方光球的磁对消将磁通量向日珥传输,引起日珥内部磁通梁痛怕荻仍黾印Ｈ甄淼淖刺与所积累的通量（或磁螺度）有关。数值结果显示,如果日珥磁通的相对增量Ｆ（或相应的磁螺度相对增量Ｈ）较小,日珥只略微上升和膨胀,并不离开光球;而对于较大的Ｆ（或Ｈ）,日 将脱离光球,悬浮在低层日冕中,在其下方形成垂直电流片。     

日冕物质抛射和太阳表面磁活动的关系

综述了近年来日冕物质抛射与耀斑、日珥、冕流和日冕暗化相关关系的研究进展，指出了这些相关关系上的一些不确定因素。同时，介绍了我们所做的部分工作，探讨了不同尺度磁活动之间的物理联系，并提出今后需要进一步解决的问题。     

太阳耀斑MHD理论简评

本文概略地回顾及评述了早期的太阳耀斑理论模型,并介绍了目前国际太阳物理界在地面高分辨观测资料和空间观测资料分析基础上对此课题研究的主要倾向。着重讨论了耀斑理论模型中的磁流体力学方面的问题,并指出了其存在的问题。     

谱线形成深度的理论及其应用（I）：贡献函数和谱线形成深度

本系列文章中给出了谱线形成深度理论的发展特别是其最新进展，分别叙述了与此理论相联系的贡献函数和响应函数的演化过程，讨论了此理论的应用特别是用于太阳矢量磁场空间三维结构的推导。在这第一篇文章中，叙述了与贡献函数相关的理论，指出了应用此理论的局限性，并讨论了唯一性问题。     

谱线形成深度的理论及其应用(Ⅰ):贡献函数和谱线形成深度

本系列文章中给出了谱线形成深度理论的发展特别是其最新进展，分别叙述了与此理论相联系的贡献函数和响应函数的演化过程，讨论了此理论的应用特别是用于太阳矢量磁场空间三维结构的推导．在这第一篇文章中，叙述了与贡献函数相夫的理论，指出了应用此理论的局限性，并讨论了唯一性问题．     

Magnetic Helicity Injection in Solar Active Regions

We present the evolution of magnetic field and its relationship with mag- netic(current)helicity in solar active regions from a series of photospheric vector magnetograms obtained by Huairou Solar Observing Station,longitudinal magne- tograms by MDI of SOHO and white light images of TRACE.The photospheric current helicity density is a quantity reflecting the local twisted magnetic field and is related to the remaining magnetic helicity in the photosphere,even if the mean current helicity density brings the general chiral property in a layer of solar active regions.As new magnetic flux emerges in active regions,changes of photospheric cur- rent helicity density with the injection of magnetic helicity into the corona from the subatmosphere can be detected,including changes in sign caused by the injection of magnetic helicity of opposite sign.Because the injection rate of magnetic helicity and photospheric current helicity density have different means in the solar atmosphere, the injected magnetic helicity is probably not proportional to the current helicity den- sity remaining in the photosphere.The evidence is that rotation of sunspots does not synchronize exactly with the twist of photospheric transverse magnetic field in some active regions(such as,delta active regions).They represent different aspects of mag- netic chirality.A combined analysis of the observational magnetic helicity parameters actually provides a relative complete picture of magnetic helicity and its transfer in the solar atmosphere.     

Coronal Magnetic Flux Rope Equilibria and Magnetic Helicity

1 INTRODUCTIONObservations show that the magnetic helicity of solar magnetic structures has a predominantsign in each hemisphere of the Sun, positive in the southern hemisphere and negative in thenorthern, regardless of the solar cycle (Rust, 1994). The magnetic helicity is strictly conservedin the frame of ideal MHD (WOltjer, 1958), and approximately conserved in the presence ofresistive dissipation and magnetic reconnection in a highly conductive plajsma (Taylor, 1974;Berger, 1984; H…     

Magnetic field, helicity and the 2000 July 14 flare in solar active region 9077

In this paper we analyse the non-potential magnetic field and the relationship with current (helicity) in the active region NOAA 9077 in 2000 July, using photospheric vector magnetograms obtained at different solar observatories and also coronal extreme-ultraviolet 171-Å images from the TRACE satellite.
We note that the shear and squeeze of magnetic field are two important indices for some flare-producing regions and can be confirmed by a sequence of photospheric vector magnetograms and EUV 171-Å features in the solar active region NOAA 9077. Evidence on the release of magnetic field near the photospheric magnetic neutral line is provided by the change of magnetic shear, electric current and current helicity in the lower solar atmosphere. It is found that the 'Bastille Day' 3B/5.7X flare on 2000 July 14 was triggered by the interaction of the different magnetic loop systems, which is relevant to the ejection of helical magnetic field from the lower solar atmosphere. The eruption of the large-scale coronal magnetic field occurs later than the decay of the highly sheared photospheric magnetic field and also current in the active region.     

Modelling the Global Solar Corona II: Coronal Evolution and Filament Chirality Comparison

This paper considers the hemispheric pattern of solar filaments using newly developed simulations of the real photospheric and 3D coronal magnetic fields over a six-month period, on a global scale. The magnetic field direction in the simulation is compared directly with the chirality of observed filaments, at their observed locations. In our model the coronal field evolves through a continuous sequence of nonlinear force-free equilibria, in response to the changing photospheric boundary conditions and the emergence of new magnetic flux. In total 119 magnetic bipoles with properties matching observed active regions are inserted. These bipoles emerge twisted and inject magnetic helicity into the solar atmosphere. When we choose the sign of this active-region helicity to match that observed in each hemisphere, the model produces the correct chirality for up to 96% of filaments, including exceptions to the hemispheric pattern. If the emerging bipoles have zero helicity, or helicity of the opposite sign, then this percentage is much reduced. In addition, the simulation produces a higher proportion of filaments with the correct chirality after longer times. This indicates that a key element in the evolution of the coronal field is its long-term memory, and the build-up and transport of helicity from low to high latitudes over many months. It highlights the importance of continuous evolution of the coronal field, rather than independent extrapolations at different times. This has significant consequences for future modelling such as that related to the origin and development of coronal mass ejections.     

Scaling law of the reduced magnetic helicity in fast streams

The reduced magnetic helicity is a quantity related to the handedness of the magnetic field fluctuations. In the present paper we study the scaling law of the reduced magnetic helicity in fast streams in the solar wind by using high-resolution magnetic field data by the Ulysses spacecraft. We show that at high frequencies both the left-hand and the right-hand helicity survives, implying that there is no predominance of a single sign. In addition, the scaling law of the magnetic helicity exhibits a strong dependence on the data set analyzed and we do not observe any universal behavior.     

Coronal activity from dynamos in astrophysical rotators

We show that a steady mean-field dynamo in astrophysical rotators leads to an outflow of relative magnetic helicity and thus magnetic energy available for particle and wind acceleration in a corona. The connection between energy and magnetic helicity arises because mean-field generation is linked to an inverse cascade of magnetic helicity. To maintain a steady state in large magnetic Reynolds number rotators, there must then be an escape of relative magnetic helicity associated with the mean field, accompanied by an equal and opposite contribution from the fluctuating field. From the helicity flow, a lower limit on the magnetic energy deposited in the corona can be estimated. Steady coronal activity including the dissipation of magnetic energy, and formation of multi-scale helical structures therefore necessarily accompanies an internal dynamo. This highlights the importance of boundary conditions which allow this to occur for non-linear astrophysical dynamo simulations. Our theoretical estimate of the power delivered by a mean-field dynamo is consistent with that inferred from observations to be delivered to the solar corona, the Galactic corona, and Seyfert 1 AGN coronae.     

太阳剩余磁场研究进展

太阳剩余磁场是指形成于太阳主序星阶段之前，深藏在太阳辐射核内部的原始磁场。由于太阳内部高电导率和准静态等因素，其剩余磁场耗散相当缓慢，而得以保留至今。太阳剩余磁场的存在不仅能够解释太阳活动的很多不对称性现象，如南北不对称性、活动经度与活动穴、低纬度冕洞和Maunder极小期等，还能通过改变自激发发电机模型的边值条件而影响整个太阳表面磁场的分布与演化。从观测结果和理论模型两方面评述了太阳剩余磁场的研究成果及最新进展，并简单讨论了进一步努力的方向。     

Magnetic Fields and Solar Activities

We discuss the study of solar magnetic fields based on the photospheric vector magnetograms of solar active regions which were obtained at Huairou Solar Observing Station near Beijing in the period of 22nd and 23th solar cycles. The measurements of the chromospheric magnetic field and the spatial configuration of the field at the lower solar atmosphere inferred by the distribution of the solar photospheric and chromospheric magnetic field. After the analysis on the formation process of delta configuration in some super active regions based on the photospheric vector magnetogram observations, some results are obtained: (1) The analysis of magnetic writhe of whole active regions cannot be limited in the strong field of sunspots, because the contribution of the fraction of decayed magnetic field is non-negligible. (2) The magnetic model of kink magnetic ropes, proposed to be generated in the subatmosphere, is not consistent with the evolution of large-scale twisted photospheric transverse magnetic field and the relationship with magnetic shear in some delta active regions completely. (3) The proposition is that the large-scale delta active regions are formed from contribution by highly sheared non-potential magnetic flux bundles generated in the subatmosphere. We present some results of a study of the magnetic helicity. We also compare these results with other data sets obtained by magnetographs (or Stokes polarimeters) at different observatories, and analyze the basic chirality of the magnetic field in the solar atmosphere.