1989年8月17日太阳边缘耀斑和速度场研究

本文利用云南天文台二维光谱仪观测的１９８９年８月１７日耀斑的Ｈβ波段光谱资料，采用多云模型的方法，得到此耀斑的观测视向速度分布，并在一定的简化和假设下，采用ＭＨＤ理论计算了几种情况下耀斑环内物质运动的视向速度分布，与观测的视向速度分布加以比较，研究和探讨耀斑环中的物质运动情况。通过分析比较，得出此耀斑环内物质运动可能属于下述两种模式：物质从环顶沿两环腿螺旋下落和物质从环足沿一环腿螺旋上升到环顶后沿另一腿螺旋下落     

一个边缘耀斑(后)环系速度场的近似计算

利用“多云模型”方法,从云南天文台二维多波段太阳光谱仪观测到的Ｈβ光谱资料中导出１９８９年８月１７日太阳西边缘的一个大的耀斑环系不同时间的视向速度场．为了解释观测速度场的主要特征,本文采用如下假设和近似：环内物质在太阳重力、磁场应力和环内气压梯度力联合作用下由环足沿螺旋磁力线上升运动．应用ＭＨＤ理论计算了它的理论速度场．通过两者的比较发现,计算出的速度场与第一时段的观测速度场基本相似,这似乎对耀斑物质蒸发模型提供了支持．     

一个边缘耀斑（后）环系速度场的近似计算

利用“多云模型”方法,从云南天台二维多波段太阳光谱仪观测到的Ｈβ光谱资料中导出１９８９年８月１７日态阳西边缘的一个大的耀斑环系不同时间的视向速度场,为了解释观测速度场的主要特征,本采用如下假设和近似：环内物质在太阳重力、磁场应力和环内气压樟率力联合作用下由环足沿螺旋磁力线上升运动,应用ＭＨＤ理论计算了它的理论经速度场,通过两的比较发现,计算出的速度场与第一时段的观测速度场基本相似,这似乎对耀     

1989年8月17日太阳边缘耀斑和速度场研究

本文云南天文台二维光谱仪观测的１９８９年８月１７日耀斑的Ｈβ波 段光谱资料，采用多云模型的方法，得到此耀斑的观测视向速度分布，并在一定的简化和假设下，采用ＭＨＤ理论计算了几种情况下光耀斑环内物质运动的视向速度分布，与观测的视向速度分布加以比较，研究和探讨耀斑环中的物质运动情况。     

1984年2月18日环状日珥和速度场

本文给出1984年2月18日耀斑后环的Hα色球和Hα-SSHG的光谱形态分析,同时给出它的二维视向速度场,并对该速度场特征给予定性解释。结果表明:(1)该环珥是一个耀斑后的拱廊(‘Post’-Flare Arch);(2)用环顶物质在重力和磁应力作用下主要沿光学厚环腿下落的假设能很好地解释观测结果。     

1984年2月18日环珥系速度场的定量计算

本文研究了在太阳重力、偶极磁压强梯度和气体压力梯度力共同作用下环珥系内物质的下落运动,并在等温、准封闭环假设下用数值方法给出了该环珥系二维视向速度场。通过将速度场的理论计算跟观测结果拟合,导出了该环系内的有关物理参数及分布。计算表明环系内密度和磁场强度对物质下落运动的影响比较明显,而温度的影响较小。     

圆面耀斑环物理量场的归算和分析

本文对云南天文台1981年5月16日3B级双带大耀斑环(0922UT)的H_α—SSHG光谱资料作了初步的数据处理。采用非线性函数的最小二乘曲线拟合方法,从光谱轮廓求得圆面耀斑环的线心光学厚度τ_0、Doppler宽度Δλ_D平均能源函数S_λ及视向速度V_(11)的二维分布,为处理具有时空序列的光谱资料提供了一种数值方法。计算结果表明,耀斑环系内的物质由环顶沿两环腿向色球层溅落;用色球蒸发模型解释环中的物质来源较为合理。     

1992年6月26日Hα耀斑后环的不均匀性和物质运动的可能解释

本文利用电流不稳定性线性理论讨论了１９９２年６月２５日至２６日耀斑后环中出现不均匀“结”状结构（“ｋｎｏｔ”或“ｂｌｏｂ”）的可能性,并且在同时考虑重力、磁力和环顶物质下落初速的情况下,理论计算了１９９２年６月２６日Ｈα耀斑后环物质运动的规律。理论计算与观测求得的视向速度随高度分布的曲线基本符合。     

两个大环状日珥群H_α单色光与光谱的同时观测

利用南京大学太阳塔,我们观测到1982年12月20日和1983年2月9日出现在日面西边缘的两个大环状日珥群。由同时获得的H_α单色光照相资料H_α、CallH·K线光谱资料测出了环内物质的视向速度分布,该分布与假定物质沿环无粘滞的自由下落推算出的视向速度分布相一致。利用H_α和K线的半宽求出了环内物质的运动温度及湍动速度,温度分布比较均匀,湍动速度随日面高度而增加。利用K线和H线线心强度之比,推算了环内物质的密度,得到氢原子密度为1.3—2.6×10~(10)cm~(-3),另外,还通过估算环珥群的总能量来讨论了环珥群与耀斑的关系。     

1989年8月17日耀斑环的视向速度场

多云模型’’是处理太阳活动体光谱不对称轮廓的有效方法,本文给出了该方法的一个具体应用实例,利用云南天文台二维多波段太阳光谱仪观测的１９８９年８月１７日耀斑环Ｈβ波段光谱资料,得到了该耀斑环的视向速度场．     

太阳运动IV型射电爆发的相干辐射模型

为解释太阳运动IV型射电爆发的相干辐射机制提出一个理论模型．从耀斑中产生的高能电子，可以被扩展上升的太阳磁流管俘获．在磁流管顶部，这些高能电子的速度分布形成为类束流速度分布，激发束流等离子体的不稳定性，并且主要直接放大O模电磁波．不稳定性增长率敏锐地依赖了日冕等离子体参数，fpe／fce和射束温度Tb，这能定性解释在太阳运动IV型射电爆发中观测到的高亮温度和高偏振度，以及宽频谱的特性．     

A comprehensive analysis of the loop prominence of 1981 April 27

We make comprehensive analysis of morphological tracings and positional measurements of Hα images, white-light sunspot photographs and chromosphere velocity field, obtained at Yunnan Observatory, and hard X-ray images obtained by the Hinotori satellite, of the loop prominence of 1981 April 27. It seems likely that the observed loop is the projection of a post-flare loop system, and the associated flare occurred on the rear side of the solar disk. A two-ribbon flare such as in the Kopp-Pneuman model can satisfactorily explain all the observed features. The occurrence of such a flare seems likely from the evidence given by the data.     

X-ray source motion along the loop in two solar flares

We explore the 3–8 keV X-ray source motion along the loop legs in two solar flares observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) on August 12 and November 28, 2002. Firstly, an artificial loop is constructed to have an outline with a fixed width wide enough to cover the X-ray sources at an energy band between 3–60 keV and at various times. Secondly, RHESSI images are reconstructed at 15 energy bands with an 8 s integration window but 1 s cadence. Thirdly, the X-ray source motions are traced from the brightness distribution along the flare loop. We find that these two events tend to start as a single source at 3–8 keV around the loop top, and then separate into two which move downward along the loop legs. These two almost reach the feet of the loop at the hard X-ray (i.e. at 25–50 keV) peak. After that, the two sources move back upward to the loop top and merge together at the same position where they began. The typical timescale is about ～70 s, and the maximum speed can reach 1000 km?s^?1. Such a downward-to-upward motion along the loop is rarely seen in the observations, and it seems to be consistent with the density evolution at the loop top, first decreasing after heating and then increasing due to evaporation.     

Magnetic reconnection and coronal transients

Every two-ribbon flare observed during the Skylab period produced an observable coronal transient, provided the flare occurred close enough to the limb. The model presented here treats these two events as a combined process. Transients that occur without flares are believed to involve magnetic fields that are too weak to produce significant chromospheric emission. Adopting the hypothesis that the rising flare loop systems observed during two-ribbon flares are exhibiting magnetic reconnection, a model of a coronal transient is proposed which incorporates this reconnection process as the driving force. When two oppositely directed field lines reconnect a lower loop is created rooted to the solar surface (the flare loop) and an upper disconnected loop is produced which is free to rise. The magnetic flux of these upper loops is proposed as the driver for the transient. The force is produced by the increase in magnetic pressure under the filament and transient.A quantitative model is developed which treats the transient configuration in terms of four distinct parts- the transient itself with its magnetic field and material, the region just below the transient but above the filament, the filament with its magnetic field, and the reconnected flux beneath the filament. Two cases are considered - one in which all the prominence material rises with the transient and one in which the material is allowed to fall out of the transient. The rate of rise of the neutral line during the reconnection process is taken from the observations of the rising X-ray flare loop system during the 29 July, 1973 flare. The MHD equations for the system are reduced to four non-linear ordinary coupled differential equations which are solved using parameters believed to be realistic for solar conditions. The calculated velocity profiles, widths, etc., agree quite well with the observed properties of coronal transients as seen in white light. Since major flares are usually associated with a filament eruption about 10–15 min before the flare and since this model associates the transient with the filament eruption, we suspect that the transient is actually initiated some time before the actual flare itself.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

The magnetic non-equilibrium of buoyant flux tubes in the solar corona

The equilibrium shape of a slender flux tube in the stratified solar atmosphere is studied. The path is determined by a balance between the downwards magnetic tension, which depends on the curvature of the loop, and the upwards buoyancy force. Previous results for untwisted slender tubes are extended to include twisted tubes embedded in an external magnetic field.The path of an untwisted tube in an atmosphere with an ambient magnetic field is calculated. For a given footpoint separation, the height of the tube is lowered by increasing the strength of the external magnetic field. If the footpoints are slowly moved apart, the tube rises, until a threshold separation is reached beyond which there is no possible equilibrium height. This threshold width does not depend on the strength of the external field.The effects of twisting up a curved loop are studied, using an extension of results obtained for slender curved tubes with a straight axis. It is shown that for a twisted tube of given width, there can be two possible values of the equilibrium height. If, however, the tube is twisted more than a certain amount or if the footpoints are too widely separated there is no equilibrium. The critical footpoint separation for non-equilibrium is smaller for a twisted tube that an untwisted one.Twisting a tube or moving its feet apart is thus likely to result in non-equilibrium, causing the tube to rise indefinitely under the influence of the unbalanced buoyant force. It is suggested that this phenomenon could be important in the preflare stage of a large two-ribbon solar flare, by causing the initial slow rise of an active region filament. As well as being involved in the onset of an erupting prominence, this non-equilibrium may also be relevant to the formation of coronal loop transients.     

Mass motions associated with Hα active region arch structures

We have studied mass motions associated with active region arch structures from observations of a developing active region near the center of the solar disk. We present a method for the computation of the line-of-sight velocity from photographs at H ± 0.5 under the assumption of Beckers' cloud model and reasonable assumptions about the Doppler width and optical depth of the arches. Some arches show motions typical to arch filaments (the material moves towards the observer near the apex of the arch and away from the observer near the footpoints), while in others the velocity field is more complex. Assuming a symmetric loop, we reconstructed the velocity vector along an arch filament. The results are consistent with the picture where material is draining out of the filament while the whole structure is ascending with a velocity near that of the apex, which does not exceed 10 km s^–1. The motion is systematically slower than expected from a free-fall model.     

Dynamics of electron beams in a coronal loop and the hard X-ray burst

A numerical simulation has been made for the dynamics of non-thermal electrons (> 10keV) injected with spatial, temporal and velocity distributions into a model coronal loop. The time variations of the spatial intensity distribution and the spectrum for the expected hard X-rays are computed for many models in order to find the important physical parameters for those characteristics.The most important one is the column density of plasma, CD, along the loop. If CD is smaller than 10²⁰ cm^–2, the expected X-rays behave like the solar impulsive hard X-ray bursts, that is the spatial maximum of X-rays shifts to the top of the loop in the later phase of the burst accompanying a spectral softening. On the other hand, if CD is greater than this value, quasi-steady decay appears in the later phase. In this case the intensity distribution of X-rays above about 20 keV along the loop shows a broad maximum away from the loop top giving an extended spatial distribution of hard X-rays, and spectral hardness is kept constant. These characteristics are similar to the solar gradual hard X-ray bursts (the so-called extended burst which is not a hot thermal gradual burst).     

Bias in velocity determinations from full-disk solar observations

Estimates for the global solar surface velocity field can be obtained from time series of full-disk solar images. However, bias is introduced by mistakes in the assumptions about the geometry of the observations, and by imperfections in the optical system. I investigate many sources of bias and determine their first-order influence on the measured velocity field (both the transverse and longitudinal components). Results are presented in analytical and pictorial form. By comparing bias velocities of unknown origin with the results, one may obtain clues to the cause of the bias.     

The rotation of magnetic loop systems in the solar atmosphere

Eclipse photographs indicate that large regions of the inner solar corona are confined in various types of closed magnetic configurations and, as a result, do not participate in the general solar wind expansion. In this paper, the rotation of initially poloidal loop configurations of this type, as influenced by differential rotation of the footpoints, is investigated. The analysis is restricted to axially symmetric fields and it is assumed that the toroidal magnetic field induced by differential rotation is small as compared to the initial poloidal field. This restricts the validity of the analysis to times less than about one month.The most interesting physical situation is that of flux tubes existing in one solar hemisphere only, one end of the tube being fixed in the photosphere at a higher latitude than the other. As a consequence, the lower end of the tube rotates at a faster rate than the upper end. Solution of the pertinent equations reveals that the angular velocity measured along a field line increases monotonically from its value at the poleward footpoint to that at the lower footpoint. The variation of angular velocity along the field depends upon the field geometry only and is not directly related to the variation of angular velocity along the solar surface between the footpoints. Depending upon the field configuration, both outward radial increases and decreases are possible. Using the Newton and Nunn model for the surface differential rotation rate, the angular velocity distribution on two particularly simple types of closed magnetic loop systems is determined analytically. It is shown that the angular velocity increases outward in the polar regions but decreases outward near the equator - leading to a decrease in differential rotation with height.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Reversal of the polarization of cyclotron radiation in a hot coronal loop

Spectropolarimetric features of thermal cyclotron radiation of solar coronal loops and the possibility of interpretation of the observed reversal of the sense of polarization of centimeter and decimeter waves are discussed. To this end, thermal cyclotron radiation is computed in terms of the simplest model of a three-dimensional hot loop (a half-torus). Such a loop is shown to be capable of changing appreciably the properties of the radiation of a solar active region at centimeter and decimeter wavelengths. A detailed analysis is performed to determine the conditions under which the radiation spectrum of an active region containing a coronal loop may have a complex pattern with several maxima or relatively narrow-band cyclotron lines, and the sense of polarization may change several times in the wavelength interval considered. These conditions are modelled by such parameters as the structure of the magnetic field, electron density, and size of the loop. The results of the computations of two-dimensional brightness temperature distributions at different wavelengths for ordinary and extraordinary waves at fixed points of the loop and the integrated parameters of the flux and polarization of radiation in terms of the model discussed are reported. Cases are considered where the line of sight is crossed by one or two loops. The expected distribution of polarization across the source in the model considered is compared to the results of RATAN-600 observations of the solar active region AR 7962 made on May 12–14, 1996.