Bimodal Distribution of Magnetic Fields and Areas of Sunspots

We applied automatic identification of sunspot umbrae and penumbrae to daily observations from the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to study their magnetic flux density (B) and area (A). The results confirm an already known logarithmic relationship between the area of sunspots and their maximum flux density. In addition, we find that the relation between average magnetic flux density ( $B_{\rm avg}$ ) and sunspot area shows a bimodal distribution: for small sunspots and pores (A≤20 millionth of solar hemisphere, MSH), $B_{\rm avg} \approx 800~\mbox{G}$ (gauss), and for large sunspots (A≥100 MSH), $B_{\rm avg}$ is about 600 G. For intermediate sunspots, average flux density linearly decreases from about 800 G to 600 G. A similar bimodal distribution was found in several other integral parameters of sunspots. We show that this bimodality can be related to different stages of sunspot penumbra formation and can be explained by the difference in average inclination of magnetic fields at the periphery of small and large sunspots.     

Observations of Rotating Sunspots from TRACE

Recent observations from TRACE in the photospheric white-light channel have shown sunspots that rotate up to 200° about their umbral centre over a period of 3–5 days. The corresponding loops in the coronal fan are often seen to twist and can erupt as flares. In an ongoing study, seven cases of rotating sunspots have been identified, two of which can be associated with sigmoid structures appearing in Yohkoh/SXT and six with events seen by GOES. This paper analyzes the rotation rates of the sunspots using TRACE white-light data. Observations from AR 9114 are presented in detail in the main text and a summary of the results for the remaining six sunspots is presented in Appendixes A–F. Discussion of the key results, particularly common features, are presented, as well as possible mechanisms for sunspot rotation. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1026138413791     

On the Facular Area Surrounding Decaying Sunspots

The change in facular area around decaying sunspots is investigated. The data are from full-disk photometric images from CFDT1 (5 arc sec pixels) obtained at the Ca ii K-line = 393.4 nm. The 31 active regions are from a list previously used to study the decay rate of sunspots. We find a weak, marginally significant relation between spot decay rate and growth of the surrounding facular region (r² = 0.1255). We conclude that, for this group of decaying sunspots, the growth or decay of the surrounding facular region was not clearly related to the decay rate of an active regions sunspots.     

On the Rotational Temperature of AlH in Sunspots

A search has been carried out for the presence of rotational lines of two bands of the (0, 0) and (1, 1) A ¹Π?–?X ¹Σ⁺ system of the AlH molecule in the high resolution Fourier Transform Spectra of sunspots observed at the National Solar Observatory at Kitt Peak. Though the presence of the AlH molecule in sunspots was confirmed by Wallace, Hinkle, and Livingston (An Atlas of Sunspot Umbral Spectra in the Visible from 15?000 to 25?000 cm^?1 (3920 to 6664 Å), Tech. Rep. 00-001, National Solar Observatory, Tucson, AZ, 2000), there is no report on the rotational temperature in the literature by identifying AlH molecular lines. The results obtained in this new search using a suitable identification technique are compared with the results reported by Wallace, Hinkle, and Livingston (2000). In view of the fact that the rotational temperatures of the molecules could be used to test photospheric and sunspot models, the effective rotational temperature for the (0, 0) band of the A?–?X system of AlH molecule is estimated by measuring the equivalent widths of well resolved spectral lines and its value justifies the existence of the AlH molecule in sunspots.     

Rotation of Plasma in Sunspots

In this paper we present the results of a sunspot rotation study using Abastumani Astrophysical Observatory photoheliogram data for 324 sunspots. The rotation amplitudes vary in theinebreak 2–64° range (with maximum at 12–14°), and the periods around 0–20 days (with maximum atinebreak 4–6 days). It could be concluded that sunspot rotations are rather inhomogeneous and asymmetric, but several types of sunspots are distinguished by their rotational parameters.During solar activity maximum, sunspot average rotation periods and amplitudes slightly increase. This can be affected by the increase of sunspot magnetic flux tube depth. So we can suppose that sunspot formation during solar activity is connected to a rise of magnetic tubes from deeper layers of the solar photosphere, strengthening the processes within the tube and causing variations in rotation.There is a linear relation between tilt-angle oscillation periods and amplitudes, showing higher amplitudes for large periods. The variations of those periods and especially amplitudes have a periodical shape for all types of sunspots and correlate well with the solar activity maxima with a phase delay of about 1–2 years.     

Accuracy and Limitations of Fitting and Stereoscopic Methods to Determine the Direction of Coronal Mass Ejections from Heliospheric Imagers Observations

Using data from the Heliospheric Imagers (HIs) onboard STEREO, it is possible to derive the direction of propagation of coronal mass ejections (CMEs) in addition to their speed with a variety of methods. For CMEs observed by both STEREO spacecraft, it is possible to derive their direction using simultaneous observations from the twin spacecraft and also, using observations from only one spacecraft with fitting methods. This makes it possible to test and compare different analysis techniques. In this article, we propose a new fitting method based on observations from one spacecraft, which we compare to the commonly used fitting method of Sheeley et al. (J. Geophys. Res. 104, 24739, 1999). We also compare the results from these two fitting methods with those from two stereoscopic methods, focusing on 12 CMEs observed simultaneously by the two STEREO spacecraft in 2008 and 2009. We find evidence that the fitting method of Sheeley et al. (J. Geophys. Res. 104, 24739, 1999) may result in significant errors in the determination of the CME direction when the CME propagates outside of 60°±20° from the Sun – spacecraft line. We expect our new fitting method to be better adapted to the analysis of halo or limb CMEs with respect to the observing spacecraft. We also find some evidence that direct triangulation in the HI fields-of-view should only be applied to CMEs propagating approximatively toward Earth (± 20° from the Sun – Earth line). Last, we address one of the possible sources of errors of fitting methods: the assumption of radial propagation. Using stereoscopic methods, we find that at least seven of the 12 studied CMEs had a heliospheric deflection of less than 20° as they propagated in the HI fields-of-view, which, we believe, validates this approximation.     

Automation of Area Measurement of Sunspots

When drawing up a database for sunspots from a large collection of white-light films, a need for the automation of the process arises. The concepts used at the automation of the area measurements of sunspots are described. As an example, sunspot groups NOAA 5521 and 5528 are processed and the areas obtained are compared to the measurements published in the literature. Similar values are obtained, except umbral areas published by Steinegger et al. (1996) which are significantly larger than ours. We find that the differences may be attributed to the fact that the definition proposed by Steinegger et al. (1996) for the penumbra–umbra border of a sunspot is not equivalent to those used for the measurements of others of the umbral area.     

日面新生黑子的经度分布

以云南天文台对５２２个太阳自转周的观测资料统计,在可见日面上新生的黑子,各个太阳活动周出现频数不等。从中筛选出面积ＣＹ≥５００的２２８群,以及ＣＹ≥１２００的２９群,它们分别都在经度上呈相对集中性,但又多随时间变化而漂移,在时间分布上无规律性。在可比的太阳第２１和２２活动周内,新生黑子对应的最强烈活动区只有８１２００和９２３９０,另外是８２４９５回转的８２５３３对应在最强烈活区,说明新生大黑子无固定的活动源。     

旋转黑子的太阳周时间延迟研究

统计结果显示23周旋转黑子的纬度随时间的变化呈蝴蝶图分布.对23周旋转黑子蝴蝶图和黑子蝴蝶图两翼的4条拟合曲线间的均方差随相位变化进行研究的结果表明:黑子蝴蝶图南北半球之间、旋转黑子蝴蝶图南北半球之间以及在同一半球旋转黑子蝴蝶图和黑子蝴蝶图之间存在着系统的时间延迟.这说明:23周南北半球太阳黑子活动不是同时发生的,南半球和北半球之间存在着系统的时间延迟或提前(相位差),且是南半球滞后于北半球;23周旋转黑子蝴蝶图和黑子蝴蝶图之间存在着相位差,且是旋转黑子蝴蝶图滞后于黑子蝴蝶图,观测滞后值略小于发电机模型预言的理论值.     

Speckle Masking Imaging of Sunspots and Pores

In recent years, speckle interferometry has been successfully applied to various solar phenomena and provides a powerful tool to study solar small-scale structures. The present investigation lays special emphasis on sunspots and sunspot pores. The observations have been performed with the Vacuum Tower Telescope (VTT) at the Observatorio del Teide (Tenerife) in the years from 1992 to 1994. Time series of high-spatial-resolution observations reveal the highly dynamical evolution of sunspot fine structures such as umbral dots, penumbral grains or the small-scale brightenings in the vicinity of sunspots observed in the wings of strong chromospheric absorption lines (moustache phenomenon). The reconstructed images show small-scale structures close to the telescopic diffraction limit of 0.16 at 550 nm. Furthermore, the high transmission of a Fabry–Pérot interferometer (FPI) as the principal optical element of a two-dimensional spectrometer allows one to reconstruct directly images taken within a passband of 0.014 nm.     

Two Populations of Sunspots: Differential Rotation

To investigate the differential rotation of sunspot groups using the Greenwich data, we propose an approach based on a statistical analysis of the histograms of particular longitudinal velocities in different latitude intervals. The general statistical velocity distributions for all such intervals are shown to be described by two rather than one normal distribution, so that two fundamental rotation modes exist simultaneously: fast and slow. The differentiality of rotation for the modes is the same: the coefficient at sin² in Faye’s law is 2.87–2.88 deg/day, while the equatorial rotation rates differ significantly, 0.27 deg/day. On the other hand, an analysis of the longitudinal velocities for the previously revealed two differing populations of sunspot groups has shown that small short-lived groups (SSGs) are associated with the fast rotation mode, while large long-lived groups (LLGs) are associated with both fast and slow modes. The results obtained not only suggest a real physical difference between the two populations of sunspots but also give new empirical data for the development of a dynamo theory, in particular, for the theory of a spatially distributed dynamo.     

太阳黑子研究的新进展

对近年来太阳黑子研究的主要成果和存在的问题作了比较全面的描述,内容涉及观测仪器和技术,黑子的精细结构、磁场、埃弗谢德效应、振荡和磁流体波动、致冷机制、形成与消亡和新发现的早期观测资料,并对今后工作方向提出了概括性的意见。     

MAG Waves in Sunspots Umbrae: Slow Waves Leaking to the Corona

The linear oscillations of a stratified atmosphere embedded in a uniform vertical magnetic field are studied here. We use a simple theoretical model, formed by the superposition of two isothermal layers, representing, respectively, i) the photosphere and the chromosphere, and ii) the corona. The bottom layer behaves, for some modes, as a resonant cavity where MAG waves are semi-trapped. We find the existence of two types of modes: 1) Fast modes which are trapped below the transition layer, 2) Mixed modes which are resonant modes in the first layer and leak part of the energy to the corona. These mixed modes have been found to be damped in the horizontal direction and can explain the observed slow modes in the corona.     

The Rotation of Sunspots During Activity Cycle 22

The solar rotation rate derived from the measurements of daily sunspot positions during activity cycle 22 (1988–1996) are presented. The averaged differential rotation is nearly symmetric with respect to the equator. The comparisons of our measurement with those for previous cycles show that the equatorial rotation rate gradually increases from cycle 18 to 22.     

Sunspots and (un)orientability of space-time

Within the framework of a globally conformally symmetric Abelian Higgs sunspot model it is shown that if there is even one sunspot present in the convection zone the (Sun's) space-time manifold becomesunorientable provided that the compatibility of the affine connection and the volume-form is demanded.     

The Shape of Sunspots and Solar Activity Cycles

Solar Physics - A new open-source software, called SunMap, has been developed to obtain synoptic maps in an easy and quick way from multiple full-disc solar images. Our objective is to provide a...     

Automated Detection, Characterization, and Tracking of Sunspots from SoHO/MDI Continuum Images

We describe a procedure for automated detection of sunspots from SoHO/MDI full-disk continuum images. The MDI Level-1.8 continuum images were first corrected for the limb darkening and stray light, and then were flat-fielded. Sunspots were extracted using a newly developed automated sunspot detection procedure, which is based on the level set, namely the selective binary and Gaussian function regularized level set (SBGFRLS) method (Zhang et al., Image Vis. Comput. 28, 668, 2010). In this method we initialize a two-dimensional level-set function and evolve it using a signed pressure force (SPF) function. For sunspot detection, the level-set function was defined twice, first for umbra and then for penumbra extraction. Using this procedure, along with the characterization of detected sunspots we have also generated tracking reports of all sunspots in a fully unsupervised manner.     

Local Helioseismology of Sunspots: Current Status and Perspectives

Mechanisms of the formation and stability of sunspots are among the longest-standing and intriguing puzzles of solar physics and astrophysics. Sunspots are controlled by subsurface dynamics, hidden from direct observations. Recently, substantial progress in our understanding of the physics of the turbulent magnetized plasma in strong-field regions has been made by using numerical simulations and local helioseismology. Both the simulations and helioseismic measurements are extremely challenging, but it is becoming clear that the key to understanding the enigma of sunspots is a synergy between models and observations. Recent observations and radiative MHD numerical models have provided a convincing explanation for the Evershed flows in sunspot penumbrae. Also, they lead to the understanding of sunspots as self-organized magnetic structures in the turbulent plasma of the upper convection zone, which are maintained by a large-scale dynamics. Local helioseismic diagnostics of sunspots still have many uncertainties, some of which are discussed in this review. However, there have been significant achievements in resolving these uncertainties, verifying the basic results by new high-resolution observations, testing the helioseismic techniques by numerical simulations, and comparing results obtained by different methods. For instance, a recent analysis of helioseismology data from the Hinode space mission has successfully resolved several uncertainties and concerns (such as the inclined-field and phase-speed filtering effects) that might affect the inferences of the subsurface wave-speed structure of sunspots and the flow pattern. It is becoming clear that for the understanding of the phenomenon of sunspots it is important to further improve the helioseismology methods and investigate the whole life cycle of active regions, from magnetic flux emergence to dissipation. The Solar Dynamics Observatory mission has started to provide data for such investigations.     

日面高纬度区域黑子

用云南天文台太阳黑子观测资料,对太阳活动１９、２０、２１、２２周及２３周上升段日面高纬度区域（大于±４０°）的黑子群进行统计。结果表明,高纬度黑子具有数量少,结构较简单,在日面存在时间不长等特点,是太阳活动周期更换的表征