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1.
We use an innovative research technique to analyze combined images from the Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric Observatory (SOHO) and the Transition Region and Coronal Explorer (TRACE). We produce a high spatial and temporal resolution simulated CDS raster or “composite” map from TRACE data and use
this composite map to jointly analyze data from both instruments. We show some of the advantages of using the “composite”
map method for coronal loop studies. We investigate two postflare loop structures. We find cool material (250 000 K) concentrated
at the tips or apex of the loops. This material is found to be above its scale height and therefore not in hydrostatic equilibrium.
The exposure times of the composite map and TRACE images are used to give an estimate of another loop’s cooling time. The
contribution to the emission in the TRACE images for the spectral lines present in its narrow passband is estimated by using
the CDS spectral data and CHIANTI to derive synthetic spectra. We obtain cospatial and cotemporal data collected by both instruments
in SOHO Joint Observations Program (JOP) 146 and show how the combination of these data can be utilized to obtain more accurate
measurements of coronal plasmas than if analyzed individually.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
2.
日冕物质抛射(Coronal Mass Ejection, CME)的检测是建立CME事件库和实现对CME在行星际传播的预报的重要前提. 通过Visual Geometry Group (VGG) 16卷积神经网络方法对日冕仪图像进行自动分类. 基于大角度光谱日冕仪(Large Angle and Spectrometric Coronagraph Experiment, LASCO) C2的白光日冕仪图像, 根据是否观测到CME对图像进行标记. 将标记分类的数据集用于VGG模型的训练, 该模型在测试集分类的准确率达到92.5%. 根据检测得到的标签结果, 结合时空连续性规则, 消除了误判区域, 有效分类出CME图像序列. 与Coordinated Data Analysis Workshops (CDAW)人工事件库比较, 分类出的CME图像序列能够较完整地包含CME事件, 且对弱CME结构有较高的检测灵敏度. 未来先进天基太阳天文台(Advanced Space-based Solar Observatory, ASO-S)卫星的莱曼阿尔法太阳望远镜将搭载有白光日冕仪(Solar Corona Imager, SCI), 使用此分类方法将该仪器产生的日冕图像按有无CME分类. 含CME标签的图像将推送给中国的各空间天气预报中心, 对CME进行预警. 相似文献
3.
日冕物质抛射(Coronal Mass Ejection, CME)是一种剧烈的太阳爆发现象, 它会对行星际空间造成严重扰动, 进而影响人类生产、生活. 基于CME的时空显著性, 将显著性检测方法引入到CME检测中, 利用结构化矩阵分解SOHO (Solar and Heliospheric Observatory)的大角度光谱日冕仪(Large Angle and Spectrometric Coronagraph Experiment, LASCO) C2的日冕图像对应的特征矩阵, 从中恢复出稀疏部分获得显著前景. 然后考虑CME运动时产生的时间显著性, 从而去除非CME结构(如冕流), 得到最终检测结果. 实验表明, 以人工目录协调数据分析中心(Coordinated Data Analysis Workshop, CDAW)检测结果为基准时, 所提方法不仅在检测CME数量上比计算机辅助跟踪软件包(Computer Aided CME Tracking Software package, CACTus)和太阳爆发事件检测系统(Solar Eruptive Event Detection System, SEEDS)有优势, 还在CME中心角度和张角宽度等特征物理参数测量上比CACTus和SEEDS更接近CDAW目录参考值. 相似文献
4.
In the present paper we report on the difference in angular sizes between radio-loud and radio-quiet CMEs. For this purpose
we compiled these two samples of events using Wind/WAVES and SOHO/LASCO observations obtained during 1996 – 2005. We show that the radio-loud CMEs are almost twice as wide
as the radio-quiet CMEs (considering expanding parts of CMEs). Furthermore, we show that the radio-quiet CMEs have a narrow
expanding bright part with a large extended diffusive structure. These results were obtained by measuring the CME widths in
three different ways. 相似文献
5.
M. L. Mays O. C. St. Cyr E. Quémerais S. Ferron J.-L. Bertaux S. Yashiro R. Howard 《Solar physics》2007,241(1):113-125
In this study, the possibility that coronal mass ejections (CMEs) may be observed in neutral Lyman-α emission was investigated.
An observing campaign was initiated for SWAN (Solar Wind ANisotropies), a Lyman-α scanning photometer on board the Solar and
Heliospheric Observatory (SOHO) dedicated to monitoring the latitude distribution of the solar wind from its imprints on the
interstellar sky background. This was part of SOHO Joint Observing Program (JOP) 159 and was an exploratory investigation
as it was not known how, or even if, CMEs interact with the solar wind and interstellar neutral hydrogen at this distance
(≈60 and 120 R
S). The study addresses the lack of methods for tracking CMEs beyond the field-of-view of current coronagraphs (30 R
S). In our first method we used LASCO, white-light coronagraphs on SOHO, and EIT, an extreme ultraviolet imaging telescope
also on SOHO, to identify CME candidates which, subject to certain criteria, should have been observable in SWAN. The criteria
included SWAN observation time and location, CME position angle, and extrapolated speed. None of the CME candidates that we
discuss were identified in the SWAN data. For our second method we analyzed all of the SWAN data for 184 runs of the observing
campaign, and this has yielded one candidate CME detection. The candidate CME appears as a dimming of the background Lyman-α
intensity representing ≈10% of the original intensity, moving radially away from the Sun. Multiple candidate CMEs observed
by LASCO and EIT were found which may have caused this dimming. Here we discuss the campaign, data analysis technique and
statistics, and the results. 相似文献
6.
A mechanism of damped oscillations of a coronal loop is investigated. The loop is treated as a thin toroidal flux rope with
two stationary photospheric footpoints, carrying both toroidal and poloidal currents. The forces and the flux-rope dynamics
are described within the framework of ideal magnetohydrodynamics (MHD). The main features of the theory are the following:
i) Oscillatory motions are determined by the Lorentz force that acts on curved current-carrying plasma structures and ii) damping is caused by drag that provides the momentum coupling between the flux rope and the ambient coronal plasma. The
oscillation is restricted to the vertical plane of the flux rope. The initial equilibrium flux rope is set into oscillation
by a pulse of upflow of the ambient plasma. The theory is applied to two events of oscillating loops observed by the Transition Region and Coronal Explorer (TRACE). It is shown that the Lorentz force and drag with a reasonable value of the coupling coefficient (c
d
) and without anomalous dissipation are able to accurately account for the observed damped oscillations. The analysis shows
that the variations in the observed intensity can be explained by the minor radial expansion and contraction. For the two
events, the values of the drag coefficient consistent with the observed damping times are in the range c
d
≈2 – 5, with specific values being dependent on parameters such as the loop density, ambient magnetic field, and the loop
geometry. This range is consistent with a previous MHD simulation study and with values used to reproduce the observed trajectories
of coronal mass ejections (CMEs). 相似文献
7.
Magnetic Causes of the Eruption of a Quiescent Filament 总被引：1，自引：0，他引：1
B. Schmieder V. Bommier R. Kitai T. Matsumoto T. T. Ishii M. Hagino H. Li L. Golub 《Solar physics》2008,247(2):321-333
During the JOP178 campaign in August 2006, we observed the disappearance of our target, a large quiescent filament located at S25°, after an observation time of three days (24 August to 26 August). Multi-wavelength instruments were operating: THEMIS/MTR (“MulTi-Raies”) vector magnetograph, TRACE (“Transition Region and Coronal Explorer”) at 171 Å and 1600 Å and Hida Domeless Solar telescope. Counter-streaming flows (+/?10 km?s?1) in the filament were detected more than 24 hours before its eruption. A slow rise of the global structure started during this time period with a velocity estimated to be of the order of 1 km?s?1. During the hour before the eruption (26 August around 09:00 UT) the velocity reached 5 km?s?1. The filament eruption is suspected to be responsible for a slow CME observed by LASCO around 21:00 UT on 26 August. No brightening in Hα or in coronal lines, no new emerging polarities in the filament channel, even with the high polarimetry sensitivity of THEMIS, were detected. We measured a relatively large decrease of the photospheric magnetic field strength of the network (from 400 G to 100 G), whose downward magnetic tension provides stability to the underlying stressed filament magnetic fields. According to some MHD models based on turbulent photospheric diffusion, this gentle decrease of magnetic strength (the tension) could act as the destabilizing mechanism which first leads to the slow filament rise and its fast eruption. 相似文献
8.
Coronal Mass Ejections (CMEs) release tremendous amounts of energy in the solar system, which has an impact on satellites, power facilities and wireless transmission. To effectively detect a CME in Large Angle Spectrometric Coronagraph (LASCO) C2 images, we propose a novel algorithm to locate the suspected CME regions, using the Extreme Learning Machine (ELM) method and taking into account the features of the grayscale and the texture. Furthermore, space–time continuity is used in the detection algorithm to exclude the false CME regions. The algorithm includes three steps: i) define the feature vector which contains textural and grayscale features of a running difference image; ii) design the detection algorithm based on the ELM method according to the feature vector; iii) improve the detection accuracy rate by using the decision rule of the space–time continuum. Experimental results show the efficiency and the superiority of the proposed algorithm in the detection of CMEs compared with other traditional methods. In addition, our algorithm is insensitive to most noise. 相似文献
9.
We consider the problem of automatically (and robustly) isolating and extracting information about waves and oscillations
observed in EUV image sequences of the solar corona with a view to near real-time application to data from the Atmospheric
Imaging Array (AIA) on the Solar Dynamics Observatory (SDO). We find that a simple coherence/travel-time based approach detects and provides a wealth of information on transverse
and longitudinal wave phenomena in the test sequences provided by the Transition Region and Coronal Explorer (TRACE). The results of the search are pruned (based on diagnostic errors) to minimize false-detections such that the remainder
provides robust measurements of waves in the solar corona, with the calculated propagation speed allowing automated distinction
between various wave modes. In this paper we discuss the technique, present results on the TRACE test sequences, and describe
how our method can be used to automatically process the enormous flow of data (≈1 Tb day−1) that will be provided by SDO/AIA.
Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users. 相似文献
10.
1 INTRODUCTIONCoronal majss ejections (CMEs) are often seen as spectacular eruptions of matter fromthe Sun which propagate outward through the heliosphere and often interact with the Earth'smagnetosphere (Hundhausen, 1997; Gosling, 1997; and references herein). It is well known thatthese interactions can have substalltial consequences on the geomagnetic environment of theEarth, sometimes resulting in damage to satellites (e.g., McAllister et al., 1996; Berdichevskyet al., 1998). CMEs… 相似文献
11.
M. Karovska B. Wood J. Chen J. Cook R. Howard 《Journal of Astrophysics and Astronomy》2000,21(3-4):403-406
We applied advanced image enhancement techniques to explore in detail the characteristics of the small-scale structures and/or
the low contrast structures in several Coronal Mass Ejections (CMEs) observed by SOHO. We highlight here the results from
our studies of the morphology and dynamical evolution of CME structures in the solar corona using two instruments on board
SOHO: LASCO and EIT. 相似文献
12.
13.
We present velocity estimates of bulk motions in the solar corona using data from the Large Angle Spectrometric Coronagraph (LASCO) aboard the Solar and Heliospheric Observatory spacecraft ( SOHO ). We describe a new technique which automatically provides a mass-weighted mean velocity profile in an entirely objective fashion without the need for individual event identification. A weighted velocity profile of this kind reflects the motion of the energetically dominant component of the coronal mass ejection (CME) mass spectrum and is of particular interest in consideration of the overall energy budget of the CME process. We consider the mean motion within three latitudinal bands centred at 0°, 20° and 40° over a one-year period around the time of solar minimum. We find terminal velocities within the LASCO field of around 300 km s−1 in all latitude bands but note a latitudinal dependence in CME evolution through the low corona prior to reaching these velocities. We find evidence that ejections in the equatorial zone undergo continuous acceleration whilst at higher latitudes a discrete burst of acceleration is seen to occur at around 4 R⊙ from the Sun's centre with relatively little acceleration thereafter. We also consider the energy deposition rates necessary to generate these profiles. 相似文献
14.
We analyze five events of the interaction of coronal mass ejections (CMEs) with the remote coronal rays located up to 90°
away from the CME as observed by the SOHO/LASCO C2 coronagraph. Using sequences of SOHO/LASCO C2 images, we estimate the kink
propagation in the coronal rays during their interaction with the corresponding CMEs ranging from 180 to 920 km s−1 within the interval of radial distances from 3 R
⊙ to 6 R
⊙. We conclude that all studied events do not correspond to the expected pattern of shock wave propagation in the corona. Coronal
ray deflection can be interpreted as the influence of the magnetic field of a moving flux rope within the CME. The motion
of a large-scale flux rope away from the Sun creates changes in the structure of surrounding field lines, which are similar
to the kink propagation along coronal rays. The retardation of the potential should be taken into account since the flux rope
moves at a high speed, comparable with the Alfvén speed. 相似文献
15.
We intend to provide a comprehensive answer to the question on whether all Coronal Mass Ejections (CMEs) have flux rope structure. To achieve this, we present a synthesis of the LASCO CME observations over the last 16 years, assisted by 3D MHD simulations of the breakout model, EUV and coronagraphic observations from STEREO and SDO, and statistics from a revised LASCO CME database. We argue that the bright loop often seen as the CME leading edge is the result of pileup at the boundary of the erupting flux rope irrespective of whether a cavity or, more generally, a three-part CME can be identified. Based on our previous work on white light shock detection and supported by the MHD simulations, we identify a new type of morphology, the ‘two-front’ morphology. It consists of a faint front followed by diffuse emission and the bright loop-like CME leading edge. We show that the faint front is caused by density compression at a wave (or possibly shock) front driven by the CME. We also present highly detailed multi-wavelength EUV observations that clarify the relative positioning of the prominence at the bottom of a coronal cavity with a clear flux rope structure. Finally, we visually check the full LASCO CME database for flux rope structures. In the process, we classify the events into two clear flux rope classes (‘three-part’, and ‘Loop’), jets and outflows (no clear structure). We find that at least 40 % of the observed CMEs have clear flux rope structures and that ～?29 % of the database entries are either misidentifications or inadequately measured and should be discarded from statistical analyses. We propose a new definition for flux rope CMEs (FR-CMEs) as a coherent magnetic, twist-carrying coronal structure with angular width of at least 40° and able to reach beyond 10 R⊙ which erupts on a time scale of a few minutes to several hours. We conclude that flux ropes are a common occurrence in CMEs and pose a challenge for future studies to identify CMEs that are clearly not FR-CMEs. 相似文献
16.
An-Qin Chen Wei-Guo Zong 《中国天文和天体物理学报》2009,9(4)
Coronal mass ejection (CME) velocities have been studied over recent decades. We present a statistical analysis of the relationship between CME velocities and X-ray fluxes of the associated flares. We study two types of CMEs. One is the FL type associ- ated only with flares, while the other is the intermediate type associated with both filament eruptions and flares. It is found that the velocities of the FL type CMEs are strongly cor- related with both the peak and the time-integrated X-ray fluxes of the associated flares. However, the correlations between the intermediate type CME velocities and the corre- sponding two parameters are poor. It is also found that the correlation between the CME velocities and the peak X-ray fluxes is stronger than that between the CME velocities and the time-integrated X-ray fluxes of the associated flares. 相似文献
17.
Simultaneous SOHO and Ground-Based Observations of a Large Eruptive Prominence and Coronal Mass Ejection 总被引：1，自引：0，他引：1
Plunkett S.P. Vourlidas A. Šimberová S. Karlický M. Kotrč P. Heinzel P. Kupryakov Yu.A. Guo W.P. Wu S.T. 《Solar physics》2000,194(2):371-391
Coronal mass ejections (CMEs) are frequently associated with erupting prominences near the solar surface. A spectacular eruption of the southern polar crown prominence was observed on 2 June 1998, accompanied by a CME that was well-observed by the LASCO coronagraphs on SOHO. The prominence was observed in its quiescent state and was followed throughout its eruption by the SOHO EIT and later by LASCO as the bright, twisted core of the CME. Ground-based H observations of the prominence were obtained at the Ondejov Observatory in the Czech Republic. A great deal of fine structure was observed within the prominence as it erupted. The prominence motion was found to rotate about its axis as it moved outward. The CME contained a helical structure that is consistent with the ejection of a magnetic flux rope from the Sun. Similar structures have been observed by LASCO in many other CMEs. The relationship of the flux rope to other structures in the CME is often not clear. In this event, the prominence clearly lies near the trailing edge of the structure identified as a flux rope. This structure can be observed from the onset of the CME in the low corona all the way out to the edge of the LASCO field of view. The initiation and evolution of the CME are modeled using a fully self-consistent, 3D axisymmetric, MHD code. 相似文献
18.
We analyzed the speed (v) distributions of 11584 coronal mass ejections (CMEs) observed by the Large Angle and Spectrometric Coronagraph Experiment on board the Solar and Heliospheric Observatory (SOHO/LASCO) in cycle 23 from 1996 to 2006. We find that the speed distributions for high-latitude (HL) and low-latitude (LL) CME events are nearly identical and to a good approximation they can be fitted with a lognormal distribution. This finding implies that statistically the same driving mechanism of a nonlinear nature is acting in both HL and LL CME events, and CMEs are intrinsically associated with the source's magnetic structure on large spatial scales. Statistically, the HL CMEs are slightly slower than the LL CMEs. For HL and LL CME events respectively, the speed distributions for accelerating and decelerating events are nearly identical and also to a good approximation they can be both fitted with a lognormal distribution, thus supplementing the results obtained by Yurchyshyn et al. 相似文献
19.
Wahab Uddin Ramesh Chandra Syed Salman Ali 《Journal of Astrophysics and Astronomy》2006,27(2-3):267-276
We observed 4B/X17.2 flare in Hα from super-active region NOAA 10486 at ARIES, Nainital. This is one of the largest flares
of current solar cycle 23, which occurred near the Sun’s center and produced extremely energetic emission almost at all wavelengths
from γ-ray to radio-waves. The flare is associated with a bright/fast full-halo earth directed CME, strong type II, type III
and type IV radio bursts, an intense proton event and GLE. This flare is well observed by SOHO, RHESSI and TRACE. Our Hα observations
show the stretching/de-twisting and eruption of helically twisted S shaped (sigmoid) filament in the south-west direction
of the active region with bright shock front followed by rapid increase in intensity and area of the gigantic flare. The flare
shows almost similar evolution in Hα, EUV and UV. We measure the speed of Hα ribbon separation and the mean value is ∼ 70
km s-1. This is used together with photospheric magnetic field to infer a magnetic reconnection rate at three HXR sources at the
flare maximum. In this paper, we also discuss the energetics of active region filament, flare and associated CME. 相似文献
20.
利用太阳射电宽带频谱仪(0．7-7．6GHz)于2001年10月19日观测到的复杂太阳射电大爆发，呈现出许多有趣的特征，结合NoRH(Nobeyama Radio Heliograph)的高空间分辨率射电成像观测及TRACE(Transition Region and Coronal Explorer)在远紫外(EUV)波段的高空间分辨率成像观测资料，分析了该爆发的射电频谱特征和微波射电源的演化以及它们与复杂的EUV日冕环系统的关系，该爆发是一个双带大耀斑的射电表征．前一部分以宽带(从厘米到米波)爆发为主，机制是回旋同步辐射，所对应的是环足源的辐射；后一部分以窄带(分米到米波)分米波爆发为主，机制是等离子体辐射和回旋共振辐射的联合，对应的是环顶源的辐射。 相似文献