RECONSTRUCTING THE SOLAR CORONAL MAGNETIC FIELD AS A FORCE-FREE MAGNETIC FIELD

We present some preliminary results on different mathematical problems encountered in attempts to reconstruct the coronal magnetic field, assumed to be in a force-free state, from its values in the photosphere. We discuss the formulations associated with these problems, and some new numerical methods that can be used to get their approximate solutions. Both the linear constant- and the nonlinear cases are considered. We also discuss the possible use of dynamical 3D MHD codes to construct approximate solutions of the equilibrium force-free equations, which are needed for testing numerical extrapolation schemes.     

从微波爆和X射线爆联合估算日冕磁场

本文假定Ｘ射线爆和微波爆有共同的起源，用它们的爆发流量资料联合估算源中的磁场强度Ｂ、离子数密度ｎｉ和视线方向深度Ｌ．以１９８１年４月２７日０８００ＵＴ的由五个峰组成的延伸爆为例进行了计算。计算结果为：从厚靶模型和热模型得到的五个峰的磁场Ｂ分别为１８６５─６５９Ｇ和７７６─２３４Ｇ；而从薄靶模型算得的Ｂ为３５─１５３Ｇ，ｎｉ为１０８─６×１０９／ｃｍ３，最大的Ｌ为３．３×１０９ｃｍ．这个爆发的Ｘ射线主源的高度在光球上１．４×１０４ｋｍ，因此从薄靶模型得到的结果较为合理，这也与五个峰的“微波富有指数”随时增加相一致的。这似乎表明，五个峰的源位于同一冕环中，能量释放从环顶沿着磁力线向色球方向传播。传播的速度可能是离子声速，因为用上述数据得到的最小的阿尔芬速度超过１０４ｋｍ／ｓ。     

ON THE GRADIENT OF CORONAL MAGNETIC FIELDS FROM RADIO OBSERVATIONS

A technique is proposed to estimate the magnetic field and its derivative in coronal layers above solar active regions. On the basis of the theory of quasi-transverse propagation of microwaves, the measurable degree of circular polarization is related to the gradient of the coronal magnetic field. The relation is applied to the analyses of a set of microwave sunspot-associated sources at the time when they reverse the sense of their circular polarization.Here we present the characteristic values of coronal fields H= 20 G, H/ l = 10^-9 G cm^-1 at a height of 10¹⁰ cm, estimated using spectral-polarization observations with the radiotelescope RATAN-600 ( =18–36 at = 2.0–4.0 cm). The steepest gradient of 2 × 10^-5 G cm^-1 at h=5 × 10⁹ cm is obtained in the case of coronal magnetic fields overlying a sunspot with a high photospheric proper motion.     

PROBLEMS AND PROGRESS IN COMPUTING THREE-DIMENSIONAL CORONAL ACTIVE REGION MAGNETIC FIELDS FROM BOUNDARY DATA

An overview of the whole process of reconstructing the coronal magnetic field from boundary data measured at the photosphere is presented. We discuss the errors and uncertainties in the data and in the data reduction process. The problems include noise in the magnetograph measurements, uncertainties in the interpretation of polarization signals, the 180° ambiguity in the transverse field, and the fact that the photosphere is not force-free. Methods for computing the three-dimensional structure of coronal active region magnetic fields, under the force-free assumption, from these boundary data, are then discussed. The methods fall into three classes: the extrapolation technique, which seeks to integrate upwards from the photosphere using only local values at the boundary; the current-field iteration technique, which propagates currents measured at the boundary along field lines, then iteratively recomputes the magnetic field due to this current distribution; and the evolutionary technique, which simulates the evolution of the coronal field, under quasi-physical resistive magnetohydrodynamic equations, as currents injected at the boundary are driven towards the observed values. The extrapolation method is mathematically ill-posed, and must be heavily smoothed to avoid exponential divergence. It may be useful for tracing low-lying field lines, but appears incapable of reconstructing the magnetic field higher in the corona. The original formulation of the current-field iteration method had problems achieving convergence, but a recent reformulation appears promising. Evolutionary methods have been applied to several real datasets, with apparent success.     

RENDERING THREE-DIMENSIONAL SOLAR CORONAL STRUCTURES

An X-ray or EUV image of the corona or chromosphere is a 2D representation of an extended 3D complex for which a general inversion process is impossible. A specific model must be incorporated in order to understand the full 3D structure. We approach this problem by modeling a set of optically-thin 3D plasma flux tubes which we render these as synthetic images. The resulting images allow the interpretation of the X-ray/EUV observations to obtain information on (1) the 3D structure of X-ray images, i.e., the geometric structure of the flux tubes, and on (2) the internal structure using specific plasma characteristics, i.e., the physical structure of the flux tubes. The data-analysis technique uses magnetograms to characterize photospheric magnetic fields and extrapolation techniques to form the field lines. Using a new set of software tools, we have generated 3D flux tube structures around these field lines and integrated the plasma emission along the line of sight to obtain a rendered image. A set of individual flux-tube images is selected by a non-negative least-squares technique to provide a match with an observed X-ray image. The scheme minimizes the squares of the differences between the synthesized image and the observed image with a non-negative constraint on the coefficients of the brightness of the individual flux-tube loops. The derived images are used to determine the specific photospheric foot points and physical data, i.e., scaling laws for densities and loop lengths. The development has led to computer efficient integration and display software that is compatible for comparison with observations (e.g., Yohkoh SXT data, NIXT, or EIT). This analysis is important in determining directly the magnetic field configuration, which provides the structure of coronal loops, and indirectly the electric currents or waves, which provide the energy for the heating of the plasma. We have used very simple assumptions (i.e., potential magnetic fields and isothermal corona) to provide an initial test of the techniques before complex models are introduced. We have separated the physical and geometric contributions of the emission for a set of flux tubes and concentrated, in this initial study, on the geometric contributions by making approximations to the physical contributions. The initial results are consistent with the scaling laws derived from the Yohkoh SXT data.     

ANALYSIS OF it YOHKOH SXT CORONAL LOOPS AND CALCULATED FORCE-FREE MAGNETIC FIELD LINES FROM VECTOR MAGNETOGRAMS

In this paper some soft X-ray loops observed by Yohkoh/SXT and extrapolated magnetic fields from the vector magnetogram data observed at the Mitaka Flare Telescope are compared and analyzed. The computed field lines generally agree with Yohkoh/SXT coronal loops. Typical examples of the magnetic field intensities, loop widths, and loop heights along field lines are presented.     

CONFIGURATION OF THE MAGNETIC FIELD IN SOLAR ACTIVE REGIONS

In this paper we present the observational results of chromospheric and photospheric magnetograms in active regions obtained at the Huairou Solar Observing Station of the Beijing Astronomical Observatory. Simultaneous observations of the chromospheric and photospheric magnetic fields enable us to construct a possible configuration of the magnetic field in the solar atmosphere. The chromospheric magnetic field shows more diffusion than the photospheric magnetic field and consists of fibril-like features. We also discuss the possible configuration of the magnetic shear in highly sheared active regions.     

THE MAGNETIC FIELD 2-D STRUCTURE OF COMET HALLEY

We discussed the 2 - D structure and the distribution of magnetic field in comet Halley. We further compared our 1 - D results of distribution along the Giotto encounter trajectory with magnetic field measurements experiment on Giott.     

磁场对辐射及中子星结构的影响

本文是近几年“攀登计划”执行情况的汇报。它概括了同步曲率辐射新机制发现的意义、解决的问题及应用前景。同时它阐明了中子星内部超强磁场存在的影响,以及可与观测相比较的效应。     

太阳黑子半影的形成和返回磁通量的来源

本文从无半影的黑子成长为带半影的黑子伴随着磁场强度增强和延伸运动这个观测事实出发，通过MHD数值模拟，证明了：（1）对流层内黑子中涡旋流动的自然形成；（2）仅在黑子表面附近磁矢才急速向外移动，最终形成我们观测到的半影磁场位形；（3）光球之上由于β迅速减少，这么小的延伸速度（0.2公里／秒）仅在β～1的光球区200公里厚的层里使磁矢有效地旋转，在约几小时至一天量级时间内将近似垂直的本影磁场向水平方向旋转，形成Osherovich所期的ReturnFlux磁位形，将注入日冕空间的本影主磁流同在色球和光球内就返回的半影磁流自然地划分开来．     

太阳磁场和速度场的研究

本文介绍了怀柔太阳学术集团于２２ 太阳周期间在太阳磁场和速度场研究方面的部分成果及对２３ 太阳活动周工作的展望     

强磁场下逆康普顿散射的偏振特性

本文在Herold和我们前一工作的基础上,讨论了强磁场中不同情况(相对论情况和非相对论情况)下的逆Compton散射的偏振特性,并与无磁场情况进行了比较,得出一些有益的结果。在研究气体,尤其是具有强磁场天体的高能X射线和γ射线,甚至光学辐射机制时,这些偏振特性必须给予充分注意。     

THE SOLAR MAGNETIC FIELD IN THREE DIMENSIONS

Historically, our understanding of the solar magnetic field has been shaped by an interplay between theoretical ideas about the subsurface dynamo and precise measurements of magnetic flux at the level of the photosphere. Today we have an unprecedented ability to measure, or to infer from measurements, properties of the magnetic field at every level from the solar interior to interplanetary space, although photospheric observations still lead the way in completeness and precision. I review the state of our capabilities to measure or calculate the magnetic field and suggest that the next major goal should be to follow specific magnetic structures in space and time from before they emerge until they can no longer be detected at any level.     

对日冕物质抛射分类的定量研究

众所周知，日冕物质抛射（CME）的性质强烈地决定于其结构，故对日冕物质抛射的结构进行强度分类，对研究日地事件有重要的意义，利用模糊综合评判方法，可对日冕物质抛射的分类进行定量研究，该方法通常需考虑多个因素，如各类CME的速度、跨度、质量和动能。将其作为评判因素集，并确定相应的隶属度函数，通过计算，可以将CME分成强（strong）、中（middle）、弱（weak）3大类，并根据隶属度值的大小，给出各类CME平均特性的相对强弱排序，分析表明模糊综合评判方法优于一般的统计方法。     

INFERENCES ON CORONAL MAGNETIC FIELDS FROM SOHO UVCS OBSERVATIONS

The characteristics of the magnetic field ubiquitously permeating the coronal plasma are still largely unknown. In this paper we analyze some aspects of coronal physics, related to the magnetic field behavior, which forthcoming SOHO UVCS observations can help better understand. To this end, three coronal structures will be examined: streamers, coronal mass ejections (CMEs), and coronal holes.As to streamers and CMEs, we show, via simulations of the Ly- and white-light emission from these objects, calculated on the basis of recent theoretical models (Wang et al., 1995), how new data from SOHO can help in advancing our knowledge of the streamer/CME magnetic configuration. Our discussion highlights also those observational signatures which might offer clues on reconnection processes in streamers' current sheets.Coronal holes (CHs) are discussed in the last section of the paper. Little is known about CH flux tube geometry, which is closely related to the behavior of the solar wind at small heliocentric distances.Indirect evidence for the flux tube spreading factors, within a few solar radii, is here examined.     

OSCILLATIONS IN THERMALLY-CONDUCTING POLYTROPIC ATMOSPHERES IN THE PRESENCE OF A VERTICAL MAGNETIC FIELD

We have investigated the normal modes of subadiabatic and superadiabatic polytropic atmospheres with constant vertical magnetic field and constant thermal conductivity. In the subadiabatic case, we found the lowest, third and fifth modes were always damped, however overstability was detected in the second and fourth modes at low values of the background magnetic field. In the superadiabatic case, instability was detected in several modes, however the effect of the change from sub to superadiabatic had little effect on the frequencies of the modes. The introduction of a variety of boundary conditions varying the degree of thermal and mechanical isolation altered the decay rates of the modes from moderately damped with rigid boundary conditions toward zero decay with the less restrictive conditions, again with essentially no effect on the oscillation frequencies. In both types of atmosphere, modes with periods in the 3-min and 5-min bands were present with magnetic fields around 3000 G, whereas only the 5-min modes were present at 2000 G.     

具奇异电流密度面的一维无力场的稳定性

从Ｎｅｗｃｏｍｂ（１９６０） 给出的直线箍缩等离子体的一维能量积分和稳定性定理出发,证明Ｌｏｗ（１９９３） 在圆柱坐标系下找到的具奇异电流密度面的一维无力场是稳定的     

太阳微波爆发区磁场强度诊断和误差分析

本文分析了前人利用Dulk和Marsh的射电微波爆发谱极大频率Vp近似式求解磁场强度B的方法（我们简称两参数法）在数学、物理上存在解不唯一和不自洽的问题，且相对误差高达-3．0±5．3．而我们最近提出的利用一套完整的微波爆发谱谱参数（Vp、β和Tbv）决定磁场的方法，亦即三参数法，具有B的唯一解和自洽解，精度高达±0．48．     

THE POLARISATION OF SECOND HARMONIC CORONAL TYPE III BURSTS

The process of second harmonic plasma emission is considered, where two simplifying approximations made in previous treatments are relaxed. The revised theory can account for strong polarisation observed in some harmonic coronal type III bursts, and predicts that a correlation between these bursts and the fastest electron beam speeds associated with type III emission should be apparent. These high observed degrees of polarisation could not be explained in the earlier theory. In most cases, polarisation in the sense of the magnetoionic o-mode is predicted. The predicted degree of polarisation is shown to be strongly dependent on the form of the Langmuir wave number spectrum, and in particular on the magnitude of the wave number offset between beam-driven and backscattered Langmuir waves.     

具有类偶极磁场的厚吸积盘模型

本文从磁流体力学基本方程组出发,讨论了具有类偶极磁场的厚吸积盘模型。其结果表明:引入这种磁场位形后,会影响盘的位形、光度和吸积率。对光度的影响是通过改变盘的位形实现的,它使盘变厚,会在厚盘的内区形成更窄更陡的漏斗状结构,这对解释类星体的高度准直性的喷流更为有利;并且还预言不对称喷流或单边喷流的存在。