晕日冕物质抛射（CME）被发现比正常的CME快得多，这是一个长期存在的难题。为了解决这个难题，我们首先研究了31个肢体CME的观测特性，这些CME显示出清晰的环形额环。观测结果显示出一种强烈的趋势，即慢CME的白光强度较弱。然后，我们进行了蒙特卡罗模拟的20 000个人工肢体CME的平均速度为$\sim$ 523 km s $^{-1}$。这些事件的汤姆逊散射的计算时，假设它们被观察到的肢体和晕事件，分别。研究发现，许多慢日冕物质抛射的白光强度随着它们从临边事件转变为晕事件而显著减弱。当强度低于背景太阳风波动时，可以认为日冕仪会忽略它们。“可探测的”晕CME的平均速度为$\sim$ 922 km s $^{-1}$，非常接近观测值。它还表明，更广泛的事件更有可能被记录下来。结果表明，晕日冕物质抛射的高平均速度是由于大部分慢事件和一部分携带较少物质的窄快事件太微弱，与太阳风波动相混合，因而没有被观测到。
英文摘要：
Halo coronal mass ejections (CMEs) were found to be significantly faster than normal CMEs, which was a long-standing puzzle. In order to solve the puzzle, we first investigate the observed properties of 31 limb CMEs that display clearly loop-shaped frontal loops. The observational results show a strong tendency that slower CMEs are weaker in the white-light intensity. Then, we perform a Monte Carlo simulation of 20 000 artificial limb CMEs that have average velocity of $\sim$523 km s$^{-1}$. The Thomson scattering of these events is calculated when they are assumed to be observed as limb and halo events, respectively. It is found that the white-light intensity of many slow CMEs becomes remarkably reduced as they turn from being viewed as a limb event to as a halo event. When the intensity is below the background solar wind fluctuation, it is assumed that they would be missed by coronagraphs. The average velocity of "detectable" halo CMEs is $\sim$922 km s$^{-1}$, very close to the observed value. It also indicates that wider events are more likely to be recorded. The results soundly suggest that the higher average velocity of halo CMEs is due to that a majority of slow events and a part of narrow fast events carrying less material are so faint that they are blended with the solar wind fluctuations, and therefore are not observed.
We report on the first detection of nonthermal radio emission associated with a polar coronal mass ejection. We call the radio emission as diffuse interplanetary radio emission (DIRE), which occurs in the decameter-hectometric wavelengths. The radio emission originates from the shock flanks that interact with nearby streamers.
We present a python-based tool to detect the occultation of background sources by foreground Solar coronal mass ejections. The tool takes as input standard celestial coordinates of the source and translates those to the Helioprojective plane, and is thus well suited for use with a wide variety of background astronomical sources. This tool provides an easy means to search through a large archival dataset for such crossings and relies on the well-tested Astropy and Sunpy modules.
On Formation Of A Shock Wave In Front Of A Coronal Mass Ejection With Velocity Exceeding The Critical One
新的研究证实了[M]中的结论。Eselevich，and V. Eselevich，2008];根据该理论，在日冕物质抛射前，存在一个沿CME传播方向扩展的扰动区，其速度$u$相对于周围日冕等离子体低于临界$u_C$。扰动区的时间差亮度（等离子体密度）在CME前向更远的距离平滑地减小。在扰动区的前部，在高于$u_C$的u处形成激波，表现为亮度差径向分布的不连续性。
Coronal mass ejections (CMEs) are huge expulsions of magnetized matter from the Sun and stars, traversing space with speeds of millions of kilometers per hour. Solar CMEs can cause severe space weather disturbances and consumer power outages on Earth, whereas stellar CMEs may even pose a hazard to the habitability of exoplanets. While CMEs ejected by our Sun can be directly imaged by white-light coronagraphs, for stars this is not possible. So far, only a few candidates for stellar CME detections are reported. Here we demonstrate a different approach, based on sudden dimmings in the extreme-ul…
We present a detailed three-dimensional (3D) view of a prominence eruption, coronal loop expansion, and coronal mass ejections (CMEs) associated with an M4.4 flare that occurred on 2011 March 8 in the active region NOAA 11165. Full-disk H$α$ images of the flare and filament ejection were successfully obtained by the Flare Monitoring Telescope (FMT) following its relocation to Ica University, Peru. Multiwavelength observation around the H$α$ line enabled us to derive the 3D velocity field of the H$α$ prominence eruption. Features in extreme ultraviolet were also obtained by the Atmospheric Imag…
Coronal mass ejections (CMEs) are the primary drivers of severe space weather disturbances in the heliosphere. Models of CME dynamics have been proposed that do not fully include the effects of magnetic reconnection on the forces driving the ejection. Both observations and numerical modeling, however, suggest that reconnection likely plays a major role in most, if not all, fast CMEs. Here, we theoretically investigate the accretion of magnetic flux onto a rising ejection by reconnection involving the ejection's background field. This reconnection alters the magnetic structure of the ejection a…
In situ measurements of interplanetary coronal mass ejection (ICME) composition, including elemental abundances and charge states of heavy ions, open a new avenue to study coronal mass ejections (CMEs) besides remote-sensing observations. The ratios between different elemental abundances can diagnose the plasma origin of CMEs (e.g., from the corona or chromosphere/photosphere) due to the first ionization potential (FIP) effect, which means elements with different FIP get fractionated between the photosphere and corona. The ratios between different charge states of a specific element can provid…
The role of active region coronal magnetic field in determining coronal mass ejection propagation direction
研究了活动区日冕磁场位形在决定日冕物质抛射（CME）传播方向中的作用。2014年1月7日，CME发生在盘中心附近的活动区11944（S09W01），与X1.2耀斑有关。采用一种新的基于偏振技术的CME重建方法，结果表明CME相对于CME源区的传播方向在2.5 R $_\odot$内的纬度上改变了28 $^\circ$，在6.5 R $_\odot$内的经度上改变了43 $^\circ$.这种显著的非径向运动与M $\ddot{o}$ stl等人（2015）的发现一致。我们使用非线性无力场（NLFFF）和位场源面（PFSS）外推方法来确定日冕磁场的位形。根据外推结果计算了不同高度处的磁能密度分布。结果表明，活动区日冕磁场对日冕物质抛射的传播方向有很强的影响。这与活动区日冕磁场本身的“通道”相一致，而不是附近结构的偏转。这些结果表明，要正确确定日冕物质抛射的传播方向，必须考虑活动区日冕磁场的位形。
Solar flares (SFs) are sudden brightening observed over the Sun surface which is associated with a large energy release. Flares with burst of Xray emission are normally followed by a mass ejection of electrons and ions from the solar atmosphere called Coronal Mass Ejections (CMEs). There is an evidence that solar magnetic field can change its configuration through reconnection and release energy, accelerating solar plasma causing SFs and CMEs. This study examines the SFs and CMEs data from SOHO and GOES satellites during the very low solar activity year of 2009 and moderately high solar activi…
Coronal Mass Ejections (CMEs) contributes to the perturbation of solar wind in the heliosphere. Thus, depending on the different phases of the solar cycle and the rate of CME occurrence, contribution of CMEs to solar wind parameters near the Earth changes. In the present study, we examine the long term occurrence rate of CMEs, their speeds, angular widths and masses. We attempt to find correlation between near sun parameters, determined using white light images from coronagraphs, with solar wind measurements near the Earth from in-situ instruments. Importantly, we attempt to find what fraction…
Physical Conditions of Coronal Plasma at the transit of a Shock driven by a Coronal Mass Ejection
本文报道了利用白光日冕图像和射电动力学谱确定由日冕物质抛射驱动的冲击波的等离子体物理参数。这里分析的事件是发生在2011年6月7日的壮观爆发，一个快速的CME，随后是色球等离子体柱的喷射，其中一部分落回太阳表面，与M2.5耀斑和II型射电爆发有关。SOHO/LASCO日冕仪（C2和C3）获得的图像被用来跟踪日冕中2-12 R $_\odot$之间的日冕物质抛射驱动的激波，角度间隔约为110 $^\circ$。在这些时间间隔，我们推导出2维（2D）的电子密度，冲击波速度和冲击压缩比的地图，我们测量的冲击倾斜角相对于径向方向。在合理的假设下，这些量被用来推断激波马赫数$M_\text{A}$和激波高度处日冕磁场强度的二维图。我们发现，在早期阶段（2-4 R $_\odot$），整个激波面是超阿尔夫文型的，而在以后（即更高的位置），它只在头部变成超阿尔夫文型的。这与观测到的II型爆发源的位置一致，这是从RDS结合来自WL的冲击运动学和日冕密度推断的。第一次，一个日冕冲击是用来获得一个2D地图的日冕磁场强度超过10 R $_\odot$高度和$\sim 110^\circ$纬度间隔。
We present an algorithm to detect the outer edges of Coronal Mass Ejection (CME) events as seen in differences of Heliospheric Imager STEREO SECCHI HI-1 images from either A or B spacecraft, as well as its implementation in Python.
Large-scale propagating fronts are frequently observed during solar eruptions, yet it is open whether they are waves or not, partly because the propagation is modulated by coronal structures, whose magnetic field we still cannot measure. However, when a front impacts coronal structures, an opportunity arises for us to look into the magnetic properties of both interacting parties in the low-$β$ corona. Here we studied large-scale EUV fronts accompanying three coronal mass ejections (CMEs), each originating from a kinking rope-like structure in the NOAA active region (AR) 12371. These eruptions …
Upcoming missions, including the James Webb Space Telescope, will soon characterize the atmospheres of terrestrial-type exoplanets in habitable zones around cool K- and M-type stars searching for atmospheric biosignatures. Recent observations suggest that the ionizing radiation and particle environment from active cool planet hosts may be detrimental for exoplanetary habitability. Since no direct information on the radiation field is available, empirical relations between signatures of stellar activity, including the sizes and magnetic fields of starspots, are often used. Here, we revisit the …
An onboard automated coronal mass ejections (CMEs) detection algorithm has been developed for Visible Emission Line Coronagraph (VELC) onboard ADITYA-L1. The aim of this algorithm is to reduce the load on telemetry by sending the high spatial ($\sim$ 2.51 arcsec pixel$^{-1}$) and temporal (1 s) resolution images of corona from 1.05 R$_{\odot}$ to 3 R$_{\odot}$, containing CMEs and rejecting others. It is based on intensity thresholding followed by an area thresholding in successive running difference images which are re-binned to lower resolution to improve signal to noise. Here we present the…
Solar coronal dimmings have been observed extensively in the past two decades. Due to their close association with coronal mass ejections (CMEs), there is a critical need to improve our understanding of the physical processes that cause dimmings as well as their relationship with CMEs. In this study, we investigate coronal dimmings by combining simulation and observational efforts. By utilizing a data-constrained global magnetohydrodynamics model (AWSoM: Alfven-wave Solar Model), we simulate coronal dimmings resulting from different CME energetics and flux rope configurations. We synthesize th…
We present a comprehensive analysis of a particular class of coronal mass ejection (CME) event, called streamer-blowout CME (SBOs). The events are characterized by a gradual swelling of the overlying streamer, lasting hours to days, followed by a slow, wide CME, generally exhibiting a 3-part structure, which leaves the streamer significantly depleted in its wake. We identify 909 SBO events in the LASCO/C2 observations between 1996 and 2015. The average blowout lasts for 40.5 hours but the evacuation can take days for some events. SBO-CMEs are wider and more massive than the average CME. Their …
Estimated relations at a shock driven by a coronal mass ejection
SOHO/LASCO C3数据的分析揭示了一个不连续性，解释为一个冲击波，在一个有限的区域内的等离子体密度径向分布在每一个前面的10个选定的日冕物质抛射（CME）沿其行进方向。在各种事件中，冲击波速度为$V\approx$ 800-2500 km s $^{-1}$。将阿尔文马赫数$M_A$对激波强度$ρ_2/ρ_1$的依赖关系（在距太阳中心$R > 10R_\odot$测得）与理想MHD计算进行比较，表明表征激波阵面内部过程的有效绝热指数$γ$在很大程度上介于2和5/3之间。这对应于运动自由度的有效数量2至3。对于地球的弓形激波和行星际无碰撞激波，也导出了类似的依赖关系，即$M_A(ρ_2/ρ_1)$。所有这些都支持了CME前的间断是无碰撞激波的假设。
We report observations of thermal emission from the frontal structure of a coronal mass ejection (CME) using data obtained with the Gauribidanur RAdioheliograPH (GRAPH) simultaneously at 80 MHz and 53 MHz on 2016 May 1. The CME was due to activity on the far-side of the Sun, but near its limb. No non-thermal radio burst activity were noticed. This provided an opportunity to observe the faint thermal radio emission from the CME, and hence directly estimate the electron density, mass, and magnetic field strength of the plasma entrained in the CME. Considering that CMEs are mostly observed only i…
We report observations of the total solar eclipse of 14 December 2020, during which a coronal mass ejection can be see n propagating. A comprehensive set of photographs covering a high dynamic range of exposure allow to characterize its dimensions. The displacement of the front can be seen occurring during the few minutes of totality.
