Solar Flux Emergence Simulations

We simulate the rise through the upper convection zone and emergence through the solar surface of initially uniform, untwisted, horizontal magnetic flux, with the same entropy as the nonmagnetic plasma, that is advected into a domain 48 Mm wide by 20 Mm deep. The magnetic field is advected upward by the diverging upflows and pulled down in the downdrafts, which produces a hierarchy of loop-like structures of increasingly smaller scale as the surface is approached. There are significant differences between the behavior of fields of 10 kG and 20 or 40 kG strength at 20 Mm depth. The 10 kG fields have little effect on the convective flows and show small magnetic-buoyancy effects, reaching the surface in the typical fluid rise time from 20 Mm depth of 32 hours. 20 and 40 kG fields significantly modify the convective flows, leading to long, thin cells of ascending fluid aligned with the magnetic field and their magnetic buoyancy makes them rise to the surface faster than the fluid rise time. The 20 kG field produces a large-scale magnetic loop that as it emerges through the surface leads to the formation of a bipolar, pore-like structure.     

A Statistical Study of Magnetic Flux Emergence in Solar Active Regions Prior to Strongest Flares

Using the data on magnetic field maps and continuum intensity for Solar Cycles 23 and 24,we explored 100 active regions (ARs) that produced M5.0 or stronger flares.We focus on the presence/absence of the emergence of magnetic flux in these ARs 2–3 days before the strong flare onset.We found that 29 ARs in the sample emerged monotonically amidst quiet-Sun.A major emergence of a new magnetic flux within a pre-existing AR yielding the formation of a complex flare-productive configuration was observ...     

磁浮现与太阳表面活动现象的关系

综述了近年来人们对磁浮现与耀斑，暗条，CME等太阳表面磁活动的相关关系的研究进展。概述了磁浮现的一些观测特性和理论研究现状。最后提出了今后对磁浮现做进一步研究工作的一些设想。     

太阳活动区的磁场观测

我们利用北京天文台太阳磁场望远镜在1983年投入试观测期间取得的资料,对该年6月份的一群黑子的磁场以及耀斑作了综合分析,得到一些结论。以光球纵场为边界条件,计算了常α无力场。根据挤压无力场耀斑模式,我们认为耀斑爆发的能量,来自异极性黑子的相互靠近。磁中性线的扭曲程度,反映了无力场的状态。     

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。     

太阳异极性磁区的相互入侵

我们在文[1]的启发下,计算了磁中性线附近异极性磁区相互入侵(或挤压)引起的等离子体动力学问题。气体初态取用流行的宁静太阳光球色球大气模型,即非等温的密度指数变化的重力分层大气。采用Lagrangian格式数值求解自洽的MHD方程,这可使入侵力学变得直观明显——磁场随流体而运动。我们的新结果是入侵流动在光球低层产生出强的水平磁场(即强的横向场),但光球高层和色球低层的磁结构却变化不大,有力地支持了文[13]提出的光球色球里可能出现磁流体力学间断面的概念。入侵确实在磁中性线附近建立了电流片,但这电流片主要在光球低层,其量级和观测一致。另外还显示垂直下降运动也可能导致异极磁区的入侵。尽管在MHD~1方程里包含了电阻耗散和热传导流,但计算证明它们对入侵力学影响不大,热传导的作用只是使气体温度分布逐渐趋于宁静太阳分布(尽管高度变了)。     

Plasma Beta above a Solar Active Region: Rethinking the Paradigm

In this paper, we present a model of the plasma beta above an active region and discuss its consequences in terms of coronal magnetic field modeling. The -plasma model is representative and derived from a collection of sources. The resulting variation with height in the solar atmosphere is used to emphasize that the assumption that the magnetic pressure dominates over the plasma pressure must be carefully employed when extrapolating the magnetic field. This paper points out (1) that the paradigm that the coronal magnetic field can be constructed from a force-free magnetic field must be used in the correct context, since the force-free region is sandwiched between two regions which have >1, (2) that the chromospheric Mgii–Civ magnetic measurements occur near the -minimum, and (3) that, moving from the photosphere upwards, can return to 1 at relatively low coronal heights, e.g., R1.2 R _s.     

Time-Dependent Stochastic Modeling of Solar Active Region Energy

A time-dependent model for the energy of a flaring solar active region is presented based on an existing stochastic jump-transition model (Wheatland and Glukhov in Astrophys. J. 494, 858, 1998; Wheatland in Astrophys. J. 679, 1621, 2008 and Solar Phys. 255, 211, 2009). The magnetic free energy of an active region is assumed to vary in time due to a prescribed (deterministic) rate of energy input and prescribed (random) jumps downwards in energy due to flares. The existing model reproduces observed flare statistics, in particular flare frequency – size and waiting-time distributions, but modeling presented to date has considered only the time-independent choices of constant energy input and constant flare-transition rates with a power-law distribution in energy. These choices may be appropriate for a solar active region producing a constant mean rate of flares. However, many solar active regions exhibit time variation in their flare productivity, as exemplified by NOAA active region (AR) 11029, observed during October – November 2009 (Wheatland in Astrophys. J. 710, 1324, 2010). Time variation is incorporated into the jump-transition model for two cases: (1) a step change in the rates of flare transitions, and (2) a step change in the rate of energy supply to the system. Analytic arguments are presented describing the qualitative behavior of the system in the two cases. In each case the system adjusts by shifting to a new stationary state over a relaxation time which is estimated analytically. The model exhibits flare-like event statistics. In each case the frequency – energy distribution is a power law for flare energies less than a time-dependent rollover set by the largest energy the system is likely to attain at a given time. The rollover is not observed if the mean free energy of the system is sufficiently large. For Case 1, the model exhibits a double exponential waiting-time distribution, corresponding to flaring at a constant mean rate during two intervals (before and after the step change), if the average energy of the system is large. For Case 2 the waiting-time distribution is a simple exponential, again provided the average energy of the system is large. Monte Carlo simulations of Case 1 are presented which confirm the estimate for the relaxation time and the expected forms of the frequency – energy and waiting-time distributions. The simulation results provide a qualitative model for observed flare statistics in AR 11029.     

Multiwavelength Study of a Solar Eruption from AR NOAA 11112 I. Flux Emergence, Sunspot Rotation and Triggering of a Solar Flare

We analyze the multiwavelength observations of an M2.9/1N flare that occurred in the active region (AR) NOAA 11112 in the vicinity of a huge filament system on 16 October 2010. SDO/HMI magnetograms reveal the emergence of a bipole (within the existing AR) 50 hours prior to the flare event. During the emergence, both the positive and negative sunspots in the bipole show translational as well as rotational motion. The positive-polarity sunspot shows significant motion/rotation in the south-westward/clockwise direction, and we see continuously pushing/sliding of the surrounding opposite-polarity field region. On the other hand, the negative-polarity sunspot moves/rotates in the westward/anticlockwise direction. The positive-polarity sunspot rotates ≈?70^° within 30 hours, whereas the one with negative polarity rotates ≈?20^° within 10 hours. SDO/AIA 94 Å EUV images show the emergence of a flux tube in the corona, consistent with the emergence of the bipole in HMI. The footpoints of the flux tube were anchored in the emerging bipole. The initial brightening starts at one of the footpoints (western) of the emerging loop system, where the positive-polarity sunspot pushes/slides towards a nearby negative-polarity field region. A high speed plasmoid ejection (speed ≈?1197 km?s^?1) was observed during the impulsive phase of the flare, which suggests magnetic reconnection of the emerging positive-polarity sunspot with the surrounding opposite-polarity field region. The entire AR shows positive-helicity injection before the flare event. Moreover, the newly emerging bipole reveals the signature of a negative (left-handed) helicity. These observations provide unique evidence of the emergence of twisted flux tubes from below the photosphere to coronal heights, triggering a flare mainly due to the interaction between the emerging positive-polarity sunspot and a nearby negative-polarity sunspot by the shearing motion of the emerging positive sunspot towards the negative one. Our observations also strongly support the idea that the rotation can most likely be attributed to the emergence of twisted magnetic fields, as proposed by recent models.     

Determination of the Topology Skeleton of Magnetic Fields in a Solar Active Region

Magnetic topology has been a key to the understanding of magnetic energy re-lease mechanism. Based on observed vector magnetograms, we have determined the three-dimensional (3D) topology skeleton of the magnetic fields in the active region NOAA 10720.The skeleton consists of six 3D magnetic nulls and a network of corresponding spines, fans,and null-null lines. For the first time, we have identified a spiral magnetic null in Sun's corona.The magnetic lines of force twisted around the spine of the null, forming a 'magnetic wreath'with excess of free magnetic energy and resembling observed brightening structures at extra-ultraviolet (EUV) wavebands. We found clear evidence of topology eruptions which are re-ferred to as catastrophic changes of topology skeleton associated with a coronal mass ejection(CME) and an explosive X-ray flare. These results shed new lights on the structural complex-ity and its role in explosive magnetic activity. The concept of flux rope has been widely used in modelling explosive magnetic activity, although their observational identity is rather ob-scure or, at least, lacking of necessary details up to date. We suggest that the magnetic wreath associated with the 3D spiral null is likely an important class of the physical entity of flux ropes.     

来自6538活动区的太阳射电米波事件

利用云南天文台声光频谱仪在1991年3月记录到的太阳射电米波辐射事件、光学活动及相关事件作了分析，得到来自6538活动区太阳射电米波事件的一些基本特性。     

Numerical Simulation of a Solar Active Region. I: Bastille Day Flare

We present three-dimensional unsteady modeling and numerical simulations of a coronal active region, carried out within the compressible single-fluid MHD approximation. We focus on AR 9077 on 14 July 2000, and the triggering of the X5.7 GOES X-ray class “Bastille Day” flare. We simulate only the lower corona, although we include a virtual photosphere and chromosphere below. The boundary conditions at the base of this layer are set using temperature maps from line intensities and line-of-sight magnetograms (SOHO/MDI). From the latter, we generate vector magnetograms using the force-free approximation; these vector magnetograms are then used to produce the boundary condition on the velocity field using a minimum energy principle (Longcope, Astrophys. J. 612, 1181, 2004). The reconnection process is modeled through a dynamical hyper-resistivity which is activated when the current exceeds a critical value (Klimas et al., J. Geophys. Res. 109, 2218, 2004). Comparing the time series of X-ray fluxes recorded by GOES with modeled time series of various mean physical variables such as current density, Poynting energy flux, or radiative loss inside the active region, we can demonstrate that the model properly captures the evolution of an active region over a day and, in particular, is able to explain the initiation of the flare at the observed time.     

The Free Energy of NOAA Solar Active Region AR 11029

The NOAA active region (AR) 11029 was a small but highly active sunspot region which produced 73 GOES soft X-ray flares during its transit of the disk in late October 2009. The flares appear to show a departure from the well-known power law frequency-size distribution. Specifically, too few GOES C-class and no M-class flares were observed by comparison with a power law distribution (Wheatland, Astrophys. J. 710, 1324, 2010). This was conjectured to be due to the region having insufficient magnetic energy to power the missing large events. We construct nonlinear force-free extrapolations of the coronal magnetic field of AR 11029 using data taken on 24 October by the SOLIS Vector SpectroMagnetograph (SOLIS/VSM) and data taken on 27 October by the Hinode Solar Optical Telescope SpectroPolarimeter (Hinode/SP). Force-free modeling with photospheric magnetogram data encounters problems, because the magnetogram data are inconsistent with a force-free model. We employ a recently developed “self-consistency” procedure which addresses this problem and accommodates uncertainties in the boundary data (Wheatland and Régnier, Astrophys. J. 700, L88, 2009). We calculate the total energy and free energy of the self-consistent solution, which provides a model for the coronal magnetic field of the active region. The free energy of the region was found to be ≈?4×10²⁹?erg on 24 October and ≈?7×10³¹?erg on 27 October. An order of magnitude scaling between RHESSI non-thermal energy and GOES peak X-ray flux is established from a sample of flares from the literature and is used to estimate flare energies from the observed GOES peak X-ray flux. Based on the scaling, we conclude that the estimated free energy of AR 11029 on 27 October when the flaring rate peaked was sufficient to power M-class or X-class flares; hence, the modeling does not appear to support the hypothesis that the absence of large flares is due to the region having limited energy.     

Solar Active Region Magnetogram Generation by Attention Generative Adversarial Networks

Learning the mapping of magnetograms and EUV images is important for understanding the solar eruption mechanism and space weather forecasting.Previous works are mainly based on the pix2pix model for full-disk magnetograms generation and obtain good performance.However,in general,we are more concerned with the magnetic field distribution in the active regions where various solar storms such as the solar flare and coronal mass ejection happen.In this paper,we fuse the self-attention mechanism with...     

Observations of Microwave Ultra-Fast Absorption Phenomena Above Solar Active Region

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Microwave and Soft X-ray Study of Solar Active Region Evolution

We have studied the properties and evolution of several active regions observed at multiple wavelengths over a period of about 10 days. We have used simultaneous microwave (1.5 and 17 GHz) and soft X-ray measurements made with the Very Large Array (VLA), the Nobeyama Radio Heliograph (NRH) and the Soft X-ray Telescope (SXT) on board the Yohkoh spacecraft, as well as photospheric magnetograms from KPNO. This is the first detailed comparison between observations at radio wavelengths differing by one order of magnitude. We have performed morphological and quantitative studies of active region properties by making inter-comparison between observations at different wavelengths and tracking the day-to-day variations. We have found good general agreement between the 1.5 and 17 GHz radio maps and the soft X-rays images. The 17 GHz emission is consistent with thermal bremsstrahlung (free-free) emission from electrons at coronal temperatures plus a small component coming from plasma at lower temperatures. We did not find any systematic limb darkening of the microwave emission from active regions. We discuss the difference between the observed microwave brightness temperature and the one expected from X-ray data and in terms of emission of a low temperature plasma at the transition region level. We found a coronal optical thickness of 10^-3 and 1 for radiation at 17 and 1.5 GHz, respectively. We have also estimated the typical coronal values of emission measure ( 5 × 10²⁸ cm^-5), electron temperature ( 4.5 × 10⁶6 K) and density ( 1.2 × 10⁹ cm₃). Assuming that the emission mechanism at 17 GHz is due to thermal free-free emission, we calculated the magnetic field in the source region using the observed degree of polarization. From the degree of polarization, we infer that the 17 GHz radiation is confined to the low-lying inner loop system of the active region. We also extrapolated the photospheric magnetic field distribution to the coronal level and found it to be in good agreement with the coronal magnetic field distribution obtained from microwave observations.     

Active Region Detection and Verification With the Solar Feature Catalogue

We describe the automated extraction of active regions (ARs) or plages from the European Grid of Solar Observations (EGSO) Solar Feature Catalogue using a region-growing technique. In this work, Hα and Ca ii K3 solar images from the Meudon Observatory and EUV solar images from the SOHO/EIT instrument were used. For better detection accuracy, the statistical properties of each quarter of a full disk solar image are used to define local intensity thresholds for an initial segmentation that helps to define AR seeds. Median filtering and morphological operations are applied to the resulting binary image in order to remove noise and to merge broken regions. The centroids of each labelled region are used as seeds, from which a region-growing procedure starts. Statistics-based local thresholding is also applied to compute upper- and lower- threshold intensity values defining the spatial extents of the regions. The detection results obtained with the resulting automated thresholding and region-growing (ATRG) procedure are compared day-by-day with the synoptic maps manually generated by the Meudon Observatory and NOAA for 2 months in 2002 and more coarsely over a 5-year period. The moderate correlation found between our detection results and those produced manually on the other data sets reveals a need for a unified active region definition. As an application of the SFC for ARs we present the tracking of the active region AR NOAA 10484 during its appearance on the solar disk from 19–26 October 2003 and compare its intensity variations for Hα and Fe xii 195 Å wavelengths.     

太阳活动区的模糊分类与活动性预测

运用模糊聚类分析的方法，研究太阳活动区特性。根据Hα、软X射线耀斑与黑子群各项特征因子的数据，进行标准化处理，分别运用模糊理论中的夹角余弦法，算术平均最小法进行标定，构造模糊相似矩阵与等价矩阵，根据模糊动态聚类分析方法，确定不同λ阈值，按照活动性强弱，对24个活动区进行分类。理论计算结果表明，不同等级类型的活动区强度预测与活动区实际活动性相一致，作为太阳活动水平预报，模糊聚类分析也是一种有效的方法。     

Solar Flux and Spectrum Measurements in the EUV Spectral Region on Board Coronas-I Satellite

There are presented data on solar emission variations in the extreme ultraviolet range?inebreak (λ < 130 nm) which were obtained on board the CORONAS-I satellite during the solar activity minimum epoch in 1994. Based on the thermoluminescent technique, the measurements were performed using the SUFR (Solar Ultraviolet Radiometer) equipment for recording the solar emission flux at λ < 130 nm. The technique provides absolute measurements. The intensity of the Heii 30.4 nm line emission was also measured on board the CORONAS by means of the Vacuum Ultraviolet Solar Spectrometer (VUSS), which uses gas-photoelectron energy and intensity analysis to register the spectrum. The characteristics of both devices are given, as well as calibration methods and the main results. The observation period may be characterized by a very low activity level. The solar flux in the region λ < 130 nm was 7.5–8 erg cm^-2 s^-1, the Lα line intensity was～ (3.3 –3.7) × 10¹¹ photon cm^-2 s^-1 and the Heii (30.4 nm) line intensity was (6–7.5) × 10⁹ photon cm^-2 s^-1. Intensive solar flares were not registered during the period of observation. During the flare of B4.5 X-ray class (30 June 1994, 01:08 UT), an increase of flux of ～ 15% was registered in the range λ < 130 nm.