CME-Flare Association Deduced from Catastrophic Model of CMEs

Based on our previous works regarding solar eruptions, we focus on the relationships among different eruptive phenomena, such as solar flares, eruptive prominences and coronal mass ejections (CMEs). The three processes show clear correlations under certain circumstances. The correlation between a CME and solar flare depends the energy that stored in the relevant magnetic structure, which is available to drive the eruption: the more energy that is stored, the better the correlation is; otherwise, the correlation is poor. The correlation between a CME and eruptive prominence, on the other hand, depends on the plasma mass concentration in the configuration prior to the eruption: if the mass concentration is significant, a CME starts with an eruptive prominence, otherwise, a CME develops an without an apparent associated eruptive prominence. These results confirm that solar flares, eruptive prominences and CMEs are different significances of a single physical process that is related to the energy release in a disrupted coronal magnetic field. The impact of gravity on CME propagation and the above correlations is also investigated. Our calculations indicate that the effect of gravity is not significant unless the strength of the background field in the disrupted magnetic configuration becomes weak, say weaker than 30 G.     

日珥上升运动和日冕物质抛射的关系

本文基于观测日珥上升运动与日冕物质抛射（CME）之间的紧密联系和我们对日珥动力学特征的理解，探讨了在背景场作用下，日珥上升时其上方盔状冕流的动力学演化规律；分析了1980年8月18日爆发日珥与对应的CME事件之间的内在关系．结果表明：（1）缓慢上升的日珥只引起盔状冕流缓慢演化；（2）加速上升日珥的加速度和末速度的大小决定形成CME事件的激烈程度；（3）CME事件的能量可能来源于爆发日环释放的磁能．理论分析与观测结果基本一致．     

Correlation between CME and Flare Parameters (with and without Type II Bursts)

CMEs and flares are the two energetic phenomena on the Sun responsible for generating shocks. Our main aim is to study the relation between the physical properties of CMEs and flares associated with and without type II radio bursts. We considered a set of 290 SOHO/LASCO CMEs associated with GOES X-ray flares observed during the period from January 1997 to December 2000. The relationship between the flares and CMEs is examined for the two sets i) with metric-type IIs and ii) without metric-type IIs. Physical properties such as rise time, duration, and strength of the flares and width, speed, and acceleration of CMEs are considered. We examined the energy relationship and temporal relationship between the CMEs and flares. First, all the events in each group were considered, and then the limb events in each group were considered separately. While there is a relationship between the temporal characteristics of flares and CME properties in the case of with-type IIs, it is absent in the case of all without-type IIs. Among all the relations studied, the correlation between flare duration and CME properties is found to be highly significant compared to the other relations. Also, the relationship between flare strength and CME speed found in the with-type II events is absent in the case of all without-type II events. However, when the limb without-type II events (with reduced time window between flare and CME) are studied separately, we found the energy relationship and the temporal relationship.     

Eit and LASCO Observations of the Initiation of a Coronal Mass Ejection

We present the first observations of the initiation of a coronal mass ejection (CME) seen on the disk of the Sun. Observations with the EIT experiment on SOHO show that the CME began in a small volume and was initially associated with slow motions of prominence material and a small brightening at one end of the prominence. Shortly afterward, the prominence was accelerated to about 100 km s^-1 and was preceded by a bright loop-like structure, which surrounded an emission void, that traveled out into the corona at a velocity of 200–400 km s^-1. These three components, the prominence, the dark void, and the bright loops are typical of CMEs when seen at distance in the corona and here are shown to be present at the earliest stages of the CME. The event was later observed to traverse the LASCO coronagraphs fields of view from 1.1 to 30 R⊙. Of particular interest is the fact that this large-scale event, spanning as much as 70 deg in latitude, originated in a volume with dimensions of roughly 35" (2.5 x 10⁴ km). Further, a disturbance that propagated across the disk and a chain of activity near the limb may also be associated with this event as well as a considerable degree of activity near the west limb.     

Numerical Magnetohydrodynamic Experiments for Testing the Physical Mechanisms of Coronal Mass Ejections Acceleration

Analysis of observations from both space-borne (LASCO/SOHO, Skylab and Solar Maximum Mission) and ground-based (Mauna Loa Observatory) instruments show that there are two types of coronal mass ejections (CMEs), fast CMEs and slow CMEs. Fast CMEs start with a high initial speed, which remains more or less constant, while slow CMEs start with a low initial speed, but show a gradual acceleration. To explain the difference between the two types of CMEs, Low and Zhang (2002) proposed that it resulted from a difference in the initial topology of the magnetic fields associated with the underlying quiescent prominences, i.e., a normal prominence configuration will lead to a fast CME, while an inverse quiescent prominence results in a slow CME. In this paper we explore a different scenario to explain the existence of fast and slow CMEs. Postulating only an inverse topology for the quiescent prominences, we show that fast and slow CMEs result from different physical processes responsible for the destabilization of the coronal magnetic field and for the initiation and launching of the CME. We use a 2.5-D, time-dependent streamer and flux-rope magnetohydrodynamic (MHD) model (Wu and Guo, 1997) and investigate three initiation processes, viz. (1) injecting of magnetic flux into the flux-rope, thereby causing an additional Lorentz force that will destabilize the streamer and launch a CME (Wu et al., 1997, 1999); (2) draining of plasma from the flux-rope and triggering a magnetic buoyancy force that causes the flux-rope to lift and launch a CME; and (3) introducing additional heating into the flux-rope, thereby simulating an active-region flux-rope accompanied by a flare to launch a CME. We present 12 numerical tests using these three driving mechanisms either alone or in various combinations. The results show that both fast and slow CMEs can be obtained from an inverse prominence configuration subjected to one or more of these three different initiation processes.     

Helical Eruptive Prominence Associated with a Pair of Overlapping CMEs on 21 April 2001

The eruption of limb prominence on 21 April 2001 associated with two coronal mass ejections (CMEs) is investigated. Hα images reveal two large-scale eruptions (a prominence body and a southern foot-point arch), both showing helical internal structure. These two eruptions are found to be spatially and temporally associated with the corresponding CMEs. The kinematics and the study of geometrical parameters of the prominence show that the eruption was quite impulsive (with peak acceleration ≈470 m s⁻²) and has taken place for relatively low pitch angle of helical threads, not exceeding tan θ≈1.2. The stability criteria of the prominence are revisited in the light of the model of Vršnak (1990, Solar Phys. 129, 295) and the analysis shows that the eruption violates the instability criteria of that model. Finally, the energy stored in the prominence circuit and the energies (kinetic, potential, and magnetic) of the associated CMEs are estimated and it is found that there was enough energy stored in the prominence to drive the two CMEs. S.S. Ali is on leave from Aligarh Muslim University, Aligarh, 202 002, India.     

Simultaneous SOHO and Ground-Based Observations of a Large Eruptive Prominence and Coronal Mass Ejection

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.     

Origins of Rolling, Twisting, and Non-radial Propagation of Eruptive Solar Events

We demonstrate that major asymmetries in erupting filaments and CMEs, namely major twists and non-radial motions are typically related to the larger-scale ambient environment around eruptive events. Our analysis of prominence eruptions observed by the STEREO, SDO, and SOHO spacecraft shows that prominence spines retain, during the initial phases, the thin ribbon-like topology they had prior to the eruption. This topology allows bending, rolling, and twisting during the early phase of the eruption, but not before. The combined ascent and initial bending of the filament ribbon is non-radial in the same general direction as for the enveloping CME. However, the non-radial motion of the filament is greater than that of the CME. In considering the global magnetic environment around CMEs, as approximated by the Potential Field Source Surface (PFSS) model, we find that the non-radial propagation of both erupting filaments and associated CMEs is correlated with the presence of nearby coronal holes, which deflect the erupting plasma and embedded fields. In addition, CME and filament motions, respectively, are guided towards weaker field regions, namely null points existing at different heights in the overlying configuration. Due to the presence of the coronal hole, the large-scale forces acting on the CME may be asymmetric. We find that the CME propagates usually non-radially in the direction of least resistance, which is always away from the coronal hole. We demonstrate these results using both low- and high-latitude examples.     

日冕物质抛射的观测性质

综述日冕物质抛射的观测和持性，简短的前言之后，给出ＣＭＥ的发现经过及统计特性，着重介绍ＣＭＥ与其他种类太阳活动的相关。然后介绍ＣＭＥ的一般特性，包括可能与ＣＭＥ相关的一些物理过程的观测特性。初步结论是：ＣＭＥ是一种演变中的磁结构现象。     

A Statistical Study on CMEs Associated with DH-Type-II Radio Bursts Based on Their Source Location (Limb and Disk Events)

We have statistically studied the 344 Coronal Mass Ejections (CMEs) associated with flares and DH-type-II radio bursts (1??C?14 MHz) during 1997??C?2008. We found that only 3?% of the total CMEs (344) compared to the general population CMEs (13208) drives DH-type-II radio bursts (Gopalswamy in Solar Eruptions and Energetic Particles, AGU Geophys. Monogr. 165, 207, 2006). Out of 344 events we have selected 236 events for further analysis. We divided the events into two groups: i) disk events (within 45° from the disk center) and ii) limb events (beyond 45° but within 90° from the disk center). We find that the average CME speed of the limb events (1370?km?s^?1) is three times, while for the disk events (1055?km?s^?1) it is two times the average speed of the general population CMEs (433?km?s^?1). The average widths of the limb events (129°) and disk events (116°) are two times greater than the average width of the general population CMEs (58°). We found a better correlation between the CME speed and width (correlation coefficient R=0.56) for the limb events than that of the disk events (R=0.47). The shock speed of the CMEs associated with DH-type-II radio bursts is found by applying Leblanc, Dulk, and Bougeret??s (Solar Phys. 183, 165, 1998) electron density model; the disk events are found to have an average speed of 1190 km?s^?1 and that of the limb events is 1275 km?s^?1. From this study we compare the CME properties between limb and disk events. The properties like CME speed, width, shock speed, and correlation between CME speed and width are found to be higher for limb events than disk events. The results in disk events are subject to projection effects, and this study stresses the importance of these effects.     

Common characteristics of CMEs and BLOBs: a new view of their possible origin

An analysis of the LASCO/SOHO data has shown that blobs are similar, in their basic characteristics, to CMEs, having a relatively small size and relatively low velocities. The formation of blobs and CMEs is usually accompanied by the process where a separate ray (or rays) of the streamer belt becomes occupied by additional anti-sunward traveling plasma of increased density. Generally the size of a CME in the plane of the streamer belt can exceed the CME size in the direction normal to the belt. Conceivably the formation mechanism of CMEs and their energetics might be associated with the energy of additional anti-sunward traveling plasma. This should be taken into account when constructing theoretical models of CMEs.     

Relationship between CME dynamics and solar flare plasma

The relationship between the velocity of CMEs and the plasma temperature of the associated X-ray solar flares is investigated.The velocity of CMEs increases with plasma temperature(R=0.82)and photon index below the break energy(R=0.60)of X-ray flares.The heating of the coronal plasma appears to be significant with respect to the kinetics of a CME from the reconnection region where the flare also occurs.We propose that the initiation and velocity of CMEs perhaps depend upon the dominant process of conversion of the magnetic field energy of the active region to heating/accelerating the coronal plasma in the reconnected loops.Results show that a flare and the associated CME are two components of one energy release system,perhaps,magnetic field free energy.     

Activity associated with the solar origin of coronal mass ejections

Solar coronal mass ejections (CMEs) observed in 1980 with the HAO Coronagraph/Polarimeter on the Solar Maximum Mission (SMM) satellite are compared with other forms of solar activity that might be physically related to the ejections. The solar phenomena checked and the method of association used were intentionally patterned after those of Munro et al.'s (1979) analysis of mass ejections observed with the Skylab coronagraph to facilitate comparison of the two epochs. Comparison of the results reveals that the types and degree of CME associations are similar near solar activity minimum and at maximum. For both epochs, most CMEs with associations had associated eruptive prominences and the proportions of association of all types of activity were similar. We also found a high percentage of association between SMM CMEs and X-ray long duration events (LDEs), in agreement with Skylab results. We conclude that most CMEs are the result of the destabilization and eruption of a prominence and its overlying coronal structure, or of a magnetic structure capable of supporting a prominence.Much of this work was performed as a Visiting Scientist at the High Altitude Observatory/NCAR.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Propagation Characteristics of CMEs Associated with Magnetic Clouds and Ejecta

We have investigated the characteristics of magnetic cloud (MC) and ejecta (EJ) associated coronal mass ejections (CMEs) based on the assumption that all CMEs have a flux rope structure. For this, we used 54 CMEs and their interplanetary counterparts (interplanetary CMEs: ICMEs) that constitute the list of events used by the NASA/LWS Coordinated Data Analysis Workshop (CDAW) on CME flux ropes. We considered the location, angular width, and speed as well as the direction parameter, D. The direction parameter quantifies the degree of asymmetry of the CME shape in coronagraph images, and shows how closely the CME propagation is directed to Earth. For the 54 CDAW events, we found the following properties of the CMEs: i) the average value of D for the 23 MCs (0.62) is larger than that for the 31 EJs (0.49), which indicates that the MC-associated CMEs propagate more directly toward the Earth than the EJ-associated CMEs; ii) comparison between the direction parameter and the source location shows that the majority of the MC-associated CMEs are ejected along the radial direction, while many of the EJ-associated CMEs are ejected non-radially; iii) the mean speed of MC-associated CMEs (946 km?s^?1) is faster than that of EJ-associated CMEs (771 km?s^?1). For seven very fast CMEs (≥?1500 km?s^?1), all CMEs with large D (≥?0.4) are associated with MCs and the CMEs with small D are associated with EJs. From the statistical analysis of CME parameters, we found the superiority of the direction parameter. Based on these results, we suggest that the CME trajectory essentially determines the observed ICME structure.     

On the Collision Nature of Two Coronal Mass Ejections: A Review

Observational and numerical studies have shown that the kinematic characteristics of two or more coronal mass ejections (CMEs) may change significantly after a CME collision. The collision of CMEs can have a different nature, i.e. inelastic, elastic, and superelastic processes, depending on their initial kinematic characteristics. In this article, we first review the existing definitions of collision types including Newton’s classical definition, the energy definition, Poisson’s definition, and Stronge’s definition, of which the first two were used in the studies of CME–CME collisions. Then, we review the recent research progresses on the nature of CME–CME collisions with the focus on which CME kinematic properties affect the collision nature. It is shown that observational analysis and numerical simulations can both yield an inelastic, perfectly inelastic, merging-like collision, or a high possibility of a superelastic collision. Meanwhile, previous studies based on a 3D collision picture suggested that a low approaching speed of two CMEs is favorable for a superelastic nature. Since CMEs are an expanding magnetized plasma structure, the CME collision process is quite complex, and we discuss this complexity. Moreover, the models used in both observational and numerical studies contain many limitations. All of the previous studies on collisions have not shown the separation of two colliding CMEs after a collision. Therefore the collision between CMEs cannot be considered as an ideal process in the context of a classical Newtonian definition. In addition, many factors are not considered in either observational analysis or numerical studies, e.g. CME-driven shocks and magnetic reconnections. Owing to the complexity of the CME collision process, a more detailed and in-depth observational analysis and simulation work are needed to fully understand the CME collision process.     

Coronal mass ejections and their association to active region flaring.

Since the discovery of coronal mass ejections (CMEs), flaring has been thought to be associated in some way with the ejection in either cause or effect. When CMEs were first discovered in the 1970s it was suggested that they were powered by solar flares (e.g., Dryer, 1982). Research since then (Harrison, 1986) has indicated that there is an associated flare that occurs shortly after the CME. To investigate this further, and making no assumption that a particular flare is causally connected to the CME, flaring activity in nine active regions that show one or more CME signatures has been studied for several hours before and after CME launch. Although the initiation of the CME may occur on size scales larger than the active region itself, definite changes are seen in the flaring activity which may be related to the ejection. This work indicates that the energy released from the active region magnetic field via flaring is greater prior to the CME launch than after.     

Relationship between CME velocities and X-ray fluxes of associated flares

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.     

Solar Sources of Interplanetary Coronal Mass Ejections During the Solar Cycle 23/24 Minimum

We examine solar sources for 20 interplanetary coronal mass ejections (ICMEs) observed in 2009 in the near-Earth solar wind. We performed a detailed analysis of coronagraph and extreme ultraviolet (EUV) observations from the Solar Terrestrial Relations Observatory (STEREO) and Solar and Heliospheric Observatory (SOHO). Our study shows that the coronagraph observations from viewpoints away from the Sun–Earth line are paramount to locate the solar sources of Earth-bound ICMEs during solar minimum. SOHO/LASCO detected only six CMEs in our sample, and only one of these CMEs was wider than 120^°. This demonstrates that observing a full or partial halo CME is not necessary to observe the ICME arrival. Although the two STEREO spacecraft had the best possible configuration for observing Earth-bound CMEs in 2009, we failed to find the associated CME for four ICMEs, and identifying the correct CME was not straightforward even for some clear ICMEs. Ten out of 16 (63 %) of the associated CMEs in our study were “stealth” CMEs, i.e. no obvious EUV on-disk activity was associated with them. Most of our stealth CMEs also lacked on-limb EUV signatures. We found that stealth CMEs generally lack the leading bright front in coronagraph images. This is in accordance with previous studies that argued that stealth CMEs form more slowly and at higher coronal altitudes than non-stealth CMEs. We suggest that at solar minimum the slow-rising CMEs do not draw enough coronal plasma around them. These CMEs are hence difficult to discern in the coronagraphic data, even when viewed close to the plane of the sky. The weak ICMEs in our study were related to both intrinsically narrow CMEs and the non-central encounters of larger CMEs. We also demonstrate that narrow CMEs (angular widths ≤?20^°) can arrive at Earth and that an unstructured CME may result in a flux rope-type ICME.     

Formation of Radio Type II Bursts During a Multiple Coronal Mass Ejection Event

We study the solar event on 27 September 2001 that consisted of three consecutive coronal mass ejections (CMEs) originating from the same active region, which were associated with several periods of radio type II burst emission at decameter–hectometer (DH) wavelengths. Our analysis shows that the first radio burst originated from a low-density environment, formed in the wake of the first, slow CME. The frequency-drift of the burst suggests a low-speed burst driver, or that the shock was not propagating along the large density gradient. There is also evidence of band-splitting within this emission lane. The origin of the first shock remains unclear, as several alternative scenarios exist. The second shock showed separate periods of enhanced radio emission. This shock could have originated from a CME bow shock, caused by the fast and accelerating second or third CME. However, a shock at CME flanks is also possible, as the density depletion caused by the three CMEs would have affected the emission frequencies and hence the radio source heights could have been lower than usual. The last type II burst period showed enhanced emission in a wider bandwidth, which was most probably due to the CME–CME interaction. Only one shock that could reliably be associated with the investigated CMEs was observed to arrive near Earth.