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.     

冕流与日冕物质抛射的关系

本文研究了卡林顿自转周１５９１ － １５９２ 中冕流偏振亮度的变化。冕流带偏振亮度的分布是不均匀的,不均匀度为１０ ％ － ５０ ％ 。无日冕物质抛射影响存在时,沿冕流带冕流的分布可持续稳定存在近两个太阳自转周。当一个日冕物质抛射伴随冕流产生时,冕流的经向角大小若大于２７°,可导致冕流尖角区顶部上升速度大于２ｋｍ／ｓ。     

KINK MODES AND CURRENT SHEETS IN CORONAL LOOPS

We present simulations of the non-linear evolution of the m=1 kink mode in line-tied coronal loops. We focus on the structure of the current concentrations which develop as a consequence of the instability in two different types of magnetic field configuration, one containing a net axial current and the other with a vanishing total axial current. In the first case, current sheets develop one third of the way from footpoint to loop apex (where the non-linear kink mode folds on itself) within the body of the current channel, while in the second case the current sheet develops at the loop apex at the interface between the current containing channel and the outer axial potential field. In both cases line-tying, while playing a stabilizing role in the linear theory, acts as a destabilizing agent for the non-linear resistive evolution. The unwrapping of magnetic field lines in the vanishing axial current model appears to be consistent with the geometry of compact recurrent loop flares.     

日珥上升运动和日冕物质抛射的关系

本文基于观测日珥上升运动与日冕物质抛射（CME）之间的紧密联系和我们对日珥动力学特征的理解，探讨了在背景场作用下，日珥上升时其上方盔状冕流的动力学演化规律；分析了1980年8月18日爆发日珥与对应的CME事件之间的内在关系．结果表明：（1）缓慢上升的日珥只引起盔状冕流缓慢演化；（2）加速上升日珥的加速度和末速度的大小决定形成CME事件的激烈程度；（3）CME事件的能量可能来源于爆发日环释放的磁能．理论分析与观测结果基本一致．     

IDEAL CURRENT LAYERS AND KINK INSTABILITY IN LINE-TIED CORONAL LOOPS

The development of the kink instability in line-tied coronal loops is studied using a cylindrical MHD code. When the twist of magnetic field lines of the initial configuration exceeds a critical value, an ideal kink mode develops and drives this unstable equilibrium towards a secondary bifurcated equilibrium containing an electric current concentration. Contrary to a periodic untied configuration where a current sheet is ideally generated, the current layer is non-singular with a non-zero thickness and a finite amplitude. This current concentration extends along all the loop length and takes the form of an helical ribbon of intense current. The numerical results give an algebraic linear-like scaling of the characteristics of the current layer (amplitude and thickness) as a function of the aspect ratio of the loop. An interpretation in terms of axial field-line bending of the three-dimensional kinked equilibrium is proposed.     

论白光太阳磁象仪的原理

本文根据在考虑磁光效应的条件下由斯托克斯参数转移方程组的数值解求得的斯托克斯参数轮廓,探讨V轮廓的不对称性和剩余圆偏振产生的原因,并论证白光磁象仪的工作原理。本文指出,V轮廓的不对称量与磁场强度和速度场精度都有关,因此文[1]和[4]的两个极端性论断都与实际情况不符。     

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。     

IMPACT AND IMPACT-LIKE STRUCTURES IN ALGERIA PART II MULTI-RINGED STRUCTURES

While Part I was devoted to the study of bowl-shaped depressions in Algeria, the present article focuses on multi-ringed structures of possible impact origin on the Algerian Sahara platform. Four structures were selected from orbital, aviation and geologic documents but only three were visited. TIN BIDER (27°36′N; 005°07′E) is a concentric multiple ring structure at least 6 km in diameter. Upper-Cretaceous sedimentary beds outside the structure dip inward a few degrees at the periphery and become extremely folded nearer the center, yet a general circular symmetry is always retained. A clearly exposed contact between upper deformed beds and underlying on-deformed beds is remarkably flat, dipping less than 10° inward. The upper beds display strong centrifugal folding. In the center of the structure Lower-Cretaceous sandstones about 0.5 km above their normal stratigraphic position are exposed. Although no shatter cones, intensive brecciation, or fracturing were observed, there is definite petrographic evidence of shock metamorphism (planar elements) in the quartz grains of the central sandstones. Tin Bider is a probable impact structure. It is the only astrobleme known with such prominent ductile deformations, a characteristic which may be due to the nature of the target materials. Detailed studies are now required to understand the mechanism of deformation of this multi-ringed structure. Its formation may be early Tertiary in age. FOUM TEGUENTOUR (26°14.5′N; 002°25′E) is an 8 km diameter bull's eye ring pattern. Although the high circularity and the morphology are consistent with an impact origin, the prominence of ductile deformation, the nature of the formations (clay-gypsum with sandstone intercalcations), the type of folds, the relationships between the structure and a surrounding plateau, and the lack of any evidence of shock effects better support a diapiric origin. MAZOULA (28°24′N; 007°49′E) is an 800 m diameter multi-ring feature with a 300 m wide anticlinal dome which rises some 30–35 m above the surrounding horizontal strata. The dome is capped by a flat-lying massive carbonate layer dipping on the flanks in accordance to the surface topography. There are no special disturbances, no fractures or breccias. Mazoula is not impact in origin but may be a Cretaceous rudistid reef and/or a salt diapir.     

冕洞与太阳活动周及地磁活动的演化关系

本文用1970－1995年的冕洞资料，分析了冕洞的分布规律，磁场极性的演化特征和冕洞的地磁效应，以及它们与太阳黑子周期的演化关系，得到了一些有意义的结论。特别指出赤道冕洞和极区冕洞具有相反的演化规律和不同的特征。     

关于太阳白光耀斑连续发射起源的讨论

白光耀斑研究近年来获得较大进展，对其连续发射起源机制目前流行三种解释．一是耀斑形成过程中所产生的色球凝聚[1-3]，二是非热粒子注入大气致氢原子非热激发和电离[4-6]，三是色球强加热所引起的对大气深层的辐射反加热[7]．这三类解释具有一个共性，即除了自身直接对连续谱     

ON THE PROBLEM OF THE RELATIONSHIP BETWEEN SOLAR FLARES AND CORONAL MASS EJECTIONS

Combination of SMM data with Mauna Loa and GOES measurements shows significant relationships between coronal mass ejections (CMEs) and solar flares, or, more precisely, long decay (duration) X-ray events (LDEs). This relationship is not understood in all its details. Although mass ejections are considered to be a more probable candidate for the role of a driver, there is a problem, namely, which of these two phenomena is cause and which is consequence. To understand this, one traditionally compares start times of CMEs and LDEs. We show that the study of the correlation between XUV line broadening and the origin of CME acceleration gives additional possibilities to solve this problem. In the EUV emission, such investigations might possibly be carried out in the framework of the SOHO program. In the soft X-rays, SMM and Yohkoh data are convenient, albeit not for the same event.     

太阳射电爆发的起因：耀斑或／和日冕物质抛射

本文分析了近二十年来的地面和空间太阳有关观测资料,得出太阳射电爆发的起因为耀斑和／ 或日冕物质抛射（ＣＭＥ） 而不仅仅是耀斑,这将有利于更深刻地了解太阳射电爆发和共生高能现象的物理过程     

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.     

活动双星的X射线冕活动

本文介绍了ＲＯＳＡＴ卫星对活动双星的观测及其观测性质,并比较活动双星的冕活动与同光谱带单层的不同,探讨次星的存在和质量转移对双量活动性的影响。     

THE CORRELATION BETWEEN SUNSPOT AND CORONAL HOLE CYCLES AND A FORECAST OF THE MAXIMUM OF SUNSPOT CYCLE 23

We have shown in previous papers that a close relationship exists between the evolution of polar coronal hole area, estimated from K-coronameter observations, and the Wolf sunspot number, with a time lag of about half a solar cycle. In this paper we study the same relationship, but with the total coronal hole area at the base of the corona as obtained from a potential field model of the coronal magnetic field, which provides a more complete series of about three solar cycles. We confirm the relationship for the two last cycles and find that the forward time shift in the coronal hole area for the best correlation with sunspot number is almost the same for cycles 21 and 22, and this shift is also the time between peaks in both series. We use this result to make an early prediction of the time and size of the sunspot maximum for solar cycle 23, and find that this should occur early in 2001 and have a magnitude of about 190, similar to that of the two previous sunspot cycles.     

SIGNATURES OF CORONAL CURRENTS IN MICROWAVE IMAGES

Microwave emission from solar active regions at frequencies above 4 GHz is dominated by gyroresonance opacity in strong coronal magnetic fields, which allows us to use radio observations to measure coronal magnetic field strengths. In this paper we demonstrate one powerful consequence of this fact: the ability to identify coronal currents from their signatures in microwave images. Specifically, we compare potential-field (i.e., current-free) extrapolations of photospheric magnetic fields with microwave images and are able to identify regions where the potential extrapolation fails to predict the magnetic field strength required to explain the microwave images. Comparison with photospheric vector magnetic field observations indicates that the location inferred for coronal currents agrees with that implied by the presence of vertical currents in the photosphere. The location, over a neutral line exhibiting strong shear, is also apparently associated with strong heating.     

DISCRETE RANDOM HEATING EVENTS IN CORONAL LOOPS

The response of the coronal plasma in a magnetic loop to the release of discrete, random amounts of energy quanta over fixed time intervals is investigated. Nanoflare heating (10²⁴ erg per event) with event lifetimes on a scale of 1–20 s are shown to be able to maintain a coronal loop at typical coronal temperatures, 2 x 10⁶ K (Parker, 1988; Kopp and Poletto, 1993). Microflare events (10²⁷ erg) observed by Porter et al. (1995) with a lifetime of approximately 1 min are also investigated and it is found that the loop apex temperature varies by at most 40% from its initial static condition. However, larger energy events of the order of 10²⁸ erg (Schmieder et al., 1994) occur too infrequently and the plasma cools to chromospheric values. The implications of time-dependent heating of the corona upon observations are also discussed.     

RECONSTRUCTION OF THE THREE-DIMENSIONAL CORONAL MAGNETIC FIELD

Studies of solar flares indicate that the mechanism of flares is magnetic in character and that the coronal magnetic field is a key to understanding solar high-energy phenomena. In our ongoing research we are conducting a systematic study of a large database of observations which includes both coronal structure (from the Soft X-ray Telescope on the Yohkoh spacecraft) and photospheric vector magnetic fields (from the Haleakala Stokes Polarimeter at Mees Solar Observatory). We compare the three-dimensional nonlinear force-free coronal magnetic field, computed from photospheric boundary data, to images of coronal structure. In this paper we outline our techniques and present results for active region AR 7220/7222. We show that the computed force-free coronal magnetic field agrees well with Yohkoh X-ray coronal loops, and we discuss the properties of the coronal magnetic field and the soft X-ray loops.     

FLOWS AND DYNAMICS IN THE CORONA OBSERVED WITH THE CORONAL DIAGNOSTIC SPECTROMETER (CDS)

EUV spectra obtained with the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) show significant flows of plasma in active region loops, both at coronal and transition region temperatures. Wavelength shifts in the coronal lines Mgix 368 Å and Mgx 624 Å corresponding to upflows in the plasma reaching velocities of 50 km s^-1 have been observed in an active region. Smaller velocities are detected in the coronal lines Fexvi 360 Å and Sixii 520 Å. Flows reaching 100 km s^-1 are observed in spectral lines formed at transition region temperatures, i.e., Ov 629 Å and Oiii 599 Å, demonstrating that both the transition region and the corona are clearly dynamic in nature. Some high velocity events show even higher velocities with line profiles corresponding to a velocity dispersion of 300–400 km s^-1. Even in the quiet Sun there are velocity fluctuations of 20 km s^-1 in transition region lines. Velocities of the magnitude presented in this paper have never previously been observed in coronal lines except in explosive events and flares. Thus, the preliminary results from the CDS spectrometer promise to put constraints on existing models of the flows and energy balance in the solar atmosphere. The present results are compared to previous attempts to observe flows in the corona.