High resolution spectropolarimetric observations of 3 sunspots taken with Hinode demonstrate the existence of supersonic downflows at or close to the umbra-penumbra boundary which have not been reported before. These downflows are confined to large patches, usually encompassing bright penumbral filaments, and have lifetimes of more than 14 hr. The presence of strong downflows in the center-side penumbra near the umbra rules out an association with the Evershed flow. Chromospheric filtergrams acquired close to the time of the spectropolarimetric measurements show large, strong, and long-lived brightenings in the neighborhood of the downflows. The photospheric intensity also exhibit persistent brightenings comparable to the quiet Sun. Interestingly, the orientation of the penumbral filaments at the site of the downflows is similar to that resulting from the reconnection process described by Ryutova et al. The existence of such downflows in the inner penumbra represents a challenge for numerical models of sunspots because they have to explain them in terms of physical processes likely affecting the chromosphere.
Context. It is unclear why there is a rather sharp boundary in sunspots between the umbra and the penumbra. Both regions exhibit magnetoconvection, manifesting in penumbral filaments in the penumbra and in umbral dots in the umbra. Aims. Here we compare the physical properties of umbral dots and penumbral filaments. Our goal is to understand how the properties of these convective features change across the boundary between the umbra and the penumbra and how this is related to the rapid increase in brightness at the umbra-penumbra boundary. Methods. We derived ensemble averages of the physical …
Observations of Supersonic Downflows Near the Umbra-Penumbra Boundary of Sunspots as Revealed by Hinode
Hinode的高分辨率分光偏振观测揭示了3个太阳黑子的本影-半影边界处存在超音速下降流，这是Louis等人（2010年）最近报道的。观察到这些下行流与明亮的半影细丝共空间，并占据大于1.6弧秒$^2$的面积。它们位于中心侧的半影，与太阳黑子具有相同的极性，这表明它们与Evershed Flow无关。在本文中，我们描述了在NOAA AR 10923中观测到的超声速，并讨论了光球以及色球增亮，这是靠近下降区。我们的观测结果表明，这种现象是由动态和充满活力的物理过程中的内部半影影响上覆的色球层，从而提供了新的见解太阳黑子的数值模型。
Convective Nature of Sunspot Penumbral Filaments: Discovery of Downflows in the Deep Photosphere
我们研究了光球层中半影暗条的速度结构，以获得黑子半影对流性质的直接证据。用1米瑞典太阳望远镜在深光球C I 5380吸收线上以高空间分辨率观测到一个太阳黑子。采用多目标多帧盲解卷积（MOMFBD）方法进行图像复原，滤除杂散光。我们在这里报告的发现，在太阳黑子半影细丝的多个位置的C I 5380的红移线。例如，明亮的暗条头部显示出更大的蓝移，周围是更暗的红移区域，暗示着翻转对流。细长的下行通道也位于明亮的半影原纤维旁边。我们的研究结果提供了最有力的证据，但在半影灯丝翻转对流的存在，并强调需要观察最深的层的半影，以揭示能量传输过程发生在那里。
Lateral downflows in sunspot penumbral filaments and their temporal evolution
我们研究的时间演化的下降流观察到的侧边缘的半影细丝在太阳黑子位于非常接近的磁盘中心。我们的分析是基于一系列的近衍射极限扫描的Fe I 617.3 nm线采取的CRisp成像分光偏振仪在瑞典1米太阳望远镜。我们计算多普勒从所观察到的强度分布使用线平分线和过滤所产生的亚音速振荡的速度图。在中心侧半影中，横向下降流到处都是小的、弱的红移斑块，靠近或沿着蓝移的流动通道的边缘。这些斑块具有间歇性的生命，并经常经历合并和破碎。横向下降流与宿主细丝一起移动，并对它们的形状变化做出反应，非常类似于宁静太阳中颗粒对流的演变。中心半影的亮度和流动结构的速度之间有很好的关系，平均而言，下降流比上升流更暗，这再次让人想起安静的太阳对流。这些结果表明，在太阳黑子半影区存在翻转对流，细长的细胞形成的细丝的流动是向上的，但非常倾斜，和弱的横向向下流动。在一般情况下，从横向下降流出现的圆偏振配置文件不显示符号反转，虽然有时我们检测到三个叶状的配置文件，这是暗示相反的磁极性的像素。
Sunspots are the longest-known manifestation of solar activity, and their magnetic nature has been known for more than a century. Despite this, the boundary between umbrae and penumbrae, the two fundamental sunspot regions, has hitherto been solely defined by an intensity threshold. Here, we aim at studying the magnetic nature of umbra-penumbra boundaries in sunspots of different sizes, morphologies, evolutionary stages, and phases of the solar cycle. We used a sample of 88 scans of the Hinode/SOT spectropolarimeter to infer the magnetic field properties in at the umbral boundaries. We defined…
A typical sunspot, as seen in white-light intensity images, has a two part structure: a dark umbra and a lighter penumbra. Such distinction primarily arises due to the different orientations of magnetic fields in these two regions. In this study, we use the Kodaikanal white-light digitized data archive to analyze the long-term evolution of umbral and penumbal area. We developed an 'automated algorithm' to uniquely identify the sunspot umbra (including the calculation of penumbra to umbra ratio) from these digitized intensity images. Our analysis reveals that the ratio increases slightly with t…
Recent numerical simulations and observations of sunspots show a significant amount of opposite polarity magnetic field within the sunspot penumbra. Most of the opposite polarity field is associated with convective downflows. We present an analysis of 3D MHD simulations through forward modeling of synthetic Stokes profiles of the Fe\sci 6301.5 Å~ and Fe\sci 6302.5 Å~ lines). The synthetic Stokes profiles are spatially and spectrally degraded considering typical instrument properties. Line bisector shifts of the Fe\sci 6301.5 Å~ line are used to determine line-of-sight velocities. Far wing magn…
Jurcak et al (2018) have reported that, in a sample of more than 100 umbral cores in sunspots, the umbral-penumbral boundary (UPB) is characterized by a remarkably narrowly-defined numerical value (1867 G) of the vertical component of the magnetic field. Gough and Tayler (1966), in their study of magneto-convection, showed that the onset of convection in the presence of a magnetic field is controlled by a parameter δ which also depends on the vertical component of the field. Combining the Jurcak et al result with various empirical models of sunspots leads us to propose the following hypothesis…
We report spectropolarimetric observations of a supersonic downflow impacting the lower atmosphere within a large sunspot umbra. This work is an extension of Schad et al. 2016 using observations acquired in the He I 10830 Angstrom triplet by the Facility Infrared Spectropolarimeter. Downflowing material accelerating along a cooled coronal loop reaches peak speeds near 200 km s$^{-1}$ and exhibits both high speed emission and absorption within the umbra, which we determine to be a consequence of the strong height dependence of the radiatively-controlled source function above the sunspot umbra. …
A Hot Downflowing Model Atmosphere For Umbral Flashes And The Physical Properties Of Their Dark Fibrils
我们执行NLTE反演在一个大的本影闪光，包括黑暗的纤维可见，在他们，并在静止的本影通过使用反演代码NICOLE上的一组全斯托克斯高分辨率的Ca II 8542 A观测的太阳黑子在磁盘中心。我们发现，暗结构的斯托克斯配置文件是不同的静态和闪光区。它们最好由在速度方面更类似于闪光大气的大气再现，即使振幅减小。我们还发现了两套解决方案，精细地适合闪光的配置文件：一组是向上流动，具有过渡区，这是更深的比在静止的情况下，并在温度略有下降之前，和第二个解决方案，在色球层中的一个较热的气氛，但具有接近声速在这样的高度下降流。这种下降流可能与日冕环的存在有关，甚至取决于日冕环的存在，日冕环植根于太阳黑子的本影，就像在分析的区域中的情况一样。类似的环最近被观察到在过渡区有超音速的下降流，这与早期的“太阳黑子羽流”一致，后者总是被发现在太阳黑子中显示出强烈的下降流。最后，我们发现，平均而言，磁场减少的闪光区，这表明冲击压力是移动的磁力线在上层。
我们研究超音速Evershed下降流在太阳黑子半影的高空间分辨率光谱偏振数据在Fe I 617.3 nm线与CRISP仪器在瑞典1米太阳望远镜。物理可观测量，如从线平分线和斯托克斯V零交叉波长计算的多普勒图，以及远红翼的斯托克斯V图，被用来寻找可能存在超音速Evershed下降流的区域。我们检索的LOS速度和磁场矢量在这些地区使用两个组件的反演所观察到的斯托克斯配置文件的帮助下的SIR代码。我们在这些区域的一生中跟踪它们，以研究它们的时间行为。最后，我们进行了统计分析检测到的超音速下降流，以表征其物理特性。超音速下降流包含在向外移动的紧凑斑块中，这些斑块位于中间和外部半影中。它们被观察为明亮的，圆形的结构，在半影细丝的外端，类似于半影颗粒。斑块在其生命周期中可能经历破碎和合并，甚至有些斑块是循环的。超音速下降流与强而垂直的磁场有关，与太阳黑子的磁场相比，磁场的极性相反。我们的研究结果表明，以超音速返回太阳表面的下行流在致密的深层突然停止并产生冲击。因此，这种冲击提高了温度，并被检测到作为一个明亮的颗粒在连续滤波图，这可以解释向外移动的颗粒在中间和外部半影的存在。
The vertical component of the magnetic field ($B_\perp$) was found to reach a constant value at the umbra-penumbra boundary of stable sunspots in a recent statistical study of Hinode/SP data. The objective of this work is to verify the existence of a constant value for $B_\perp$ at the umbra-penumbra boundary from ground-based data in the near-infrared wavelengths and to determine its value for GREGOR Infrared Spectrograph (GRIS) data. This is the first statistical study on the Jurcak criterion with ground-based data, and we compare it with the results from Hinode and HMI data. Eleven spectrop…
We study the long-term behaviour of sunspot penumbra to umbra area ratio by analyzing the recently digitized Kodaikanal white-light data (1923-2011). We implement an automatic umbra extraction method and compute the ratio over eight solar cycles (Cycles 16-23). Although the average ratio doesn't show any variation with spot latitudes, cycle phases and strengths, it increases from 5.5 to 6 as the sunspot size increases from 100 $μ$hem to 2000 $μ$hem. Interestingly, our analysis also reveals that this ratio for smaller sunspots (area $<$ 100 $μ$hem) does not have any long-term systematic trend w…
The ratio of penumbral to umbral area of sunspots is an important topic for solar and geophysical studies. Hathaway (Solar Physics, 286, 347, 2013) found a curious behaviour in this parameter for small sunspot groups (areas smaller than 100 millionths of solar hemisphere, msh) using records from Royal Greenwich Observatory (RGO). Hathaway showed that penumbra-umbra ratio decreased smoothly from more than 7 in 1905 to lower than 3 by 1930 and then increased to almost 8 in 1961. Thus, Hathaway proposed the existence of a secular variation in the penumbra-umbra area ratio. In order to confirm tha…
Context. It has been reported that the boundary between the umbra and the penumbra of sunspots occurs at a canonical value of the strength of the vertical magnetic field, independently of the size of the spot. This critical field strength is interpreted as to be the threshold for the onset of magnetoconvection. Aims. Here we investigate the reasons why this criterion, also called the Jurčák criterion in the literature, does not always identify the boundary between umbra and penumbra. Methods. We perform a statistical analysis of 23 sunspots observed with Hinode/SOT. We compare the properties o…
It was empirically determined that the umbra-penumbra boundaries of stable sunspots are characterized by a constant value of the vertical magnetic field. We analyzed the evolution of the photospheric magnetic field properties of a decaying sunspot belonging to NOAA 11277 between August 28 - September 3, 2011. The observations were acquired with the spectropolarimeter on-board of the Hinode satellite. We aim to proof the validity of the constant vertical magnetic-field boundary between the umbra and penumbra in decaying sunspots. A spectral-line inversion technique was used to infer the magneti…
To better understand the formation and decay of sunspot penumbra, we studied the evolution of sunspots in the three regions of the active-region NOAA 12673 in detail. The evolution of sunspots in the three regions were all involved in the interaction of two magnetic field systems: the pre-existing magnetic field system and the later emerging magnetic field system. Through analyzing the photospheric magnetic field properties, it is found that the formation of the penumbra originated from the newly emerging magnetic bipole that were trapped in the photosphere. The change of magnetic fields in pe…
The Maunder Minimum (MM) was a prolonged period of low solar activity that occurred between 1645 and 1715. The true level of solar activity corresponding to this epoch is still a matter of debate. In order to compare solar activity during the MM with that of other epochs, we have evaluated the umbra-penumbra area ratio (U/P hereafter) during the MM. Thus, we have analyzed 196 sunspot drawings including 48 different sunspots observed during the period 1660-1709. The mode value of the ratio obtained from the occurrence frequency distribution lies between 0.15 and 0.25. Furthermore, the median an…
We analyse a sunspot simulation in an effort to understand the origin of the convective instabilities giving rise to the penumbral and umbral distinct regimes. We applied the criterion from Gough \& Tayler (1966), accounting for the stabilising effect of the vertical magnetic field to investigate the convective instabilities in a MURaM sunspot simulation. We find: (1) a highly unstable shallow layer right beneath the surface extending all over the simulation box in which convection is triggered by radiative cooling in the photosphere; (2) a deep umbral core (beneath -5 Mm) stabilised against o…
Precursor of Sunspot Penumbral Formation discovered with Hinode SOT Observations
我们目前的观测的一个间接的签名，这将有助于了解太阳黑子半影的形成过程。日之出太阳光学望远镜成功地捕捉到了一个太阳黑子从小孔到一个大的发育良好的太阳黑子的整个演化过程，其中半影出现在NOAA活动区11039的一个新兴通量区。我们发现在Ca II H图像中，在本影周围形成半影之前，围绕本影（孔）的环形区（宽度为3”-5”）。半影的发展似乎是为了填补环形区。环形带显示弱磁图信号，意味着那里的磁通量较小或磁场高度倾斜。移动预先存在的环境磁场岛，使其分布在环形区的外边缘，并且不进入该区域。在该区域没有强烈的系统性流动模式，但我们偶尔观察到小的磁通量斑块流出。观测结果表明，环形带不同于黑子沟流区，它代表了色球层的结构。我们的结论是，环形带反映了形成的磁冠覆盖在周围的区域在色球水平的本影，在光球水平的半影形成之前。半影的形成过程需要考虑色球层中的磁场结构。
Context. The solar chromosphere and the lower transition region is believed to play a crucial role in the heating of the solar corona. Models that describe the chromosphere (and the lower transition region), accounting for its highly dynamic and structured character are, so far, found to be lacking. This is partly due to the breakdown of complete frequency redistribution in the chromospheric layers and also because of the difficulty in obtaining complete sets of observations that adequately constrain the solar atmosphere at all relevant heights. Aims. We aim to obtain semi-empirical model atmo…
The analyses of sunspot observations revealed a fundamental magnetic property of the umbral boundary, the invariance of the vertical component of the magnetic field. We aim to analyse the magnetic properties of the umbra-penumbra boundary in simulated sunspots and thus assess their similarity to observed sunspots. Also, we aim to investigate the role of plasma $β$ and the ratio of kinetic to magnetic energy in simulated sunspots on the convective motions. We use a set of non-grey simulation runs of sunspots with the MURaM code. These data are used to synthesise the Stokes profiles that are the…
A closer look at a coronal loop rooted in a sunspot umbra
太阳日冕中的极紫外线（EUV）和X射线环连接着磁场活动增强的区域，但它们通常不会植根于太阳黑子的黑暗阴影中，因为那里发现的强磁场抑制了对流。这意味着，只要没有光桥或本影点，进入高层大气的磁能坡印廷通量在本影内就不重要。在这里，我们报告了一个罕见的观测日冕环植根于黑暗的本影的太阳黑子没有任何痕迹的光桥或本影点。我们使用的狭缝颚图像和光谱数据从IRIS和集中的线配置文件的O IV和Si IV，显示持久的强红移成分的循环植根于本影。利用O-IV的比值，我们可以估计密度，从而研究质量通量。通过AIA的EUV通道提供这些观测的日冕背景和温度诊断。日冕环，嵌入在较冷的下降流，主机超音速下降流。超过100公里秒的速度$^{-1}$是在相同的数量级的过渡区线的O IV和Si IV，甚至可以看到在色球Mg II线的速度相当。在足点$1"$内的投影距离处，我们看到激波过渡到较小的下降流速度，约为15 km s $^{-1}$，这与静止等温激波的质量守恒是一致的。我们没有看到能量输入到环中的直接证据，因为环植根于本影的黑暗均匀部分，附近没有光桥或本影点。因此，人们可能会得出结论，我们看到的是从循环另一端的足点驱动的虹吸流。然而，对于最终结果，需要在另一个足点处具有类似质量的数据，但这太远而不能被IRIS视场覆盖。
Solar active regions show a wide variety of oscillatory phenomena. The presence of the magnetic field leads to the appearance of several wave modes, whose behavior is determined by the sunspot thermal and magnetic structure. We aim to study the relation between the umbral and penumbral waves observed at the high photosphere and the magnetic field topology of the sunspot. Observations of the sunspot in active region NOAA 12662 obtained with the GREGOR telescope (Observatorio del Teide, Spain) were acquired on 2017 June 17. The data set includes a temporal series in the Fe I 5435 Å line obtained…
KRONOS II: Solar-like Umbra and Penumbra Properties on the Young Sun V1298~Tau
Michigan State University（密歇根州立大学）；Massachusetts Institute of Technology（麻省理工学院）；Arizona State University（亚利桑那州立大学）；Vanderbilt University（范德堡大学）；Max Planck Institute for Astronomy (MPIA)（马克斯·普朗克天文学研究所）；National Astronomical Observatory of Japan（日本国立天文台）
利用 JWST NIRISS/SOSS 掩星观测年轻行星 V1298 Tau bcd，通过星食事件光谱分析，发现宿主星 V1298~Tau 的黑子具有类似太阳的本影和半影结构，温度分别为 3265-3436 K 和 4388-4659 K，且本影面积占比约 30%。
12 stable single sunspots were investigated in two aspects. The outer boundaries of the sunspots umbra were determined by an independent mathematical method and the vertical component of the magnetic field at these boundaries was found. We analyzed data from the SDO station using the segments of the continuum and magnetic field. It is shown that in a wide range of sunspot fields, the field average along the contour changes weakly, while the vertical component of the magnetic field itself, in a particular spot, changes significantly along the defined contour which reflects the fibrous structure…
