A statistical study of CME-associated flare during the solar cycle 24

We investigate on the relationship between flares and coronal mass ejections (CMEs) in which a flare started before and after the CME events which differ in their physical properties, indicating potentially different initiation mechanisms. The physical properties of two types flare-correlated CME remain an interesting and important question in space weather. We study the relationship between flares and CMEs using a different approach requiring both temporal and spatial constraints during the period from December 1, 2008 to April 30, 2017 in which the CMEs data were acquired by SOHO/LASCO (Solar and Heliospheric Observatory/Large Angle Spectrometric Coronagraph) over the solar cycle 24. The soft X-ray flare flux data, such as flare class, location, onset time and integrated flux, are collected from Geostationary Environmental satellite (GOES) and XRT Flare catalogs. We selected 307 CMEs-flares pairs applying simultaneously temporal and spatial constraints in all events for the distinguish between two associated CME-flare types. We study the correlated properties of coincident flares and CMEs during this period, specifically separating the sample into two types: flares that precede a CME and flares that follow a CME. We found an opposite correlation relationship between the acceleration and velocity of CMEs in the After- and Before-CMEs events. We found a log-log relation between the width and mass of CMEs in the two associated types. The CMEs and flares properties show that there were significant differences in all physical parameters such as (mass, angular width, kinetic energy, speed and acceleration) between two flare-associated CME types.     

A statistical study of post-flare-associated CME events

We present a statistical study of post-flare-associated CMEs (PFA-CMEs) during the period from 1996 to 2010. By investigating all CMEs and X-ray flares, respectively, in the LASCO and GOES archives, we found 15875 CMEs of which masses are well measured and 25112 X-ray flares of which positions are determined from their optical counterparts. Under certain temporal and spatial criteria of these CMEs and solar flare events, 291PFA-CMEs events have been selected. Linking the flare fluxes with CME speeds of these paired events, we found that there is a reasonable positive linear relation between the CME linear speed and associated flare flux. The results show also the CME width increases as the flux of its associated solar flare increases. Besides we found that there is a fine positive linear relation between the CME mass and its width. Matching the flare fluxes with CME masses of these paired events, we find the CME mass increases as the flux of its associated solar flare increases. Finally we find the PFA-CME events are in regular more decelerated than the other CMEs.     

Analysis of a long-duration AR throughout five solar rotations: Magnetic properties and ejective events

Coronal mass ejections (CMEs), which are among the most magnificent solar eruptions, are a major driver of space weather and can thus affect diverse human technologies. Different processes have been proposed to explain the initiation and release of CMEs from solar active regions (ARs), without reaching consensus on which is the predominant scenario, and thus rendering impossible to accurately predict when a CME is going to erupt from a given AR. To investigate AR magnetic properties that favor CMEs production, we employ multi-spacecraft data to analyze a long duration AR (NOAA 11089, 11100, 11106, 11112 and 11121) throughout its complete lifetime, spanning five Carrington rotations from July to November 2010. We use data from the Solar Dynamics Observatory to study the evolution of the AR magnetic properties during the five near-side passages, and a proxy to follow the magnetic flux changes when no magnetograms are available, i.e. during far-side transits. The ejectivity is studied by characterizing the angular widths, speeds and masses of 108 CMEs that we associated to the AR, when examining a 124-day period. Such an ejectivity tracking was possible thanks to the multi-viewpoint images provided by the Solar-Terrestrial Relations Observatory and Solar and Heliospheric Observatory in a quasi-quadrature configuration. We also inspected the X-ray flares registered by the GOES satellite and found 162 to be associated to the AR under study. Given the substantial number of ejections studied, we use a statistical approach instead of a single-event analysis. We found three well defined periods of very high CMEs activity and two periods with no mass ejections that are preceded or accompanied by characteristic changes in the AR magnetic flux, free magnetic energy and/or presence of electric currents. Our large sample of CMEs and long term study of a single AR, provide further evidence relating AR magnetic activity to CME and Flare production.     

The CME-productivity associated with flares from two active regions

We report on two flare-productive adjacent active regions (ARs), with different levels of coronal mass ejection (CME) association. AR 10039 and AR 10044 produced strong X-ray flares during their disk passages. We examined the CME association rate of X-ray flares and found it to be different between the two ARs. AR 10039 was CME-rich with 72% association with flares, while AR 10044 was CME-poor with an association rate of only 14%. CMEs from the CME-rich AR were faster and wider than the ones from the CME-poor AR. The flare activity of AR 10044 was temporally concentrated over a short interval and spatially localized over a compact area between the major sun spots. We suggest that different pre-eruption evolution and magnetic configuration in the two regions might have contributed to the difference between the two ARs.     

米波Ⅲ型爆发与日冕物质抛射

对澳大利亚Culgoora天文台射电频谱仪在太阳活动第23周峰年期间记录到的米波Ⅲ型爆发(20～420 MHz),与日冕物质抛射(CME)、Hα耀斑及相关事件进行了统计分析,发现米波Ⅲ型爆发与CME的关系没有Ⅱ、Ⅳ型爆发与CME的关系密切;米波Ⅲ型爆发发生的时间在CME之前25～30 min最多;72%的CME事件伴随长寿命的Hα耀斑.从这些观测特征出发,对米波Ⅲ型爆发、CME和Hα耀斑进行了定性的解释.      

A study on radio-loud interacting/non-interacting CMEs-associated SEPs and solar flares

We have established a data set of 58 major hybrid SEP events associated with meter-to-decahectometer wavelength (m-to-DH) type II bursts, solar flares, and radio-load CMEs during the period of 1997–2014. The main focus of our study is to address the following two questions: Does the interaction of CMEs play a role in the enhancement of SEP intensity? Is there any difference in the seed population, and parent eruptions in the SEP events with and without CME interactions? Hence, the sample of 58 events is classified into two sets: (i) 35 non-interacting-CME-associated SEP events; (ii) 23 interacting-CME-associated SEP events. All the characteristics of SEPs, their associated CMEs/flares and the relationships between them are statistically analyzed and compared. Some of the basic attributes and relative elemental abundances (Fe/O ratios) of the both the sets are also compared. The results indicate that the seed particles in non-interacting-CME-associated SEP events are mostly from solar wind/coronal materials. But in the case of interacting-CME-associated SEP events, it may be associated with both flare material from preceding flares and coronal materials from solar wind/preceding CMEs. The correlation studies reveal that there are clear correlations between logarithmic peak intensity of SEP events and properties of CMEs (space speed: cc?=?0.56) and solar flares (peak intensity: cc?=?0.40; integrated flux: cc?=?0.52) for non-interacting-CME-associated SEP events. But these correlations are absent for the interacting-CME-associated events. In addition, the results suggest that interaction of primary CMEs with their preceding CMEs plays an important role in the enhancement of peak intensity of SEPs at least for a set of m-to-DH type II bursts associated SEP events.     

Driving major solar flares and eruptions: A review

This review focuses on the processes that energize and trigger M- and X-class solar flares and associated flux-rope destabilizations. Numerical modeling of specific solar regions is hampered by uncertain coronal-field reconstructions and by poorly understood magnetic reconnection; these limitations result in uncertain estimates of field topology, energy, and helicity. The primary advances in understanding field destabilizations therefore come from the combination of generic numerical experiments with interpretation of sets of observations. These suggest a critical role for the emergence of twisted flux ropes into pre-existing strong field for many, if not all, of the active regions that produce M- or X-class flares. The flux and internal twist of the emerging ropes appear to play as important a role in determining whether an eruption will develop predominantly as flare, confined eruption, or CME, as do the properties of the embedding field. Based on reviewed literature, I outline a scenario for major flares and eruptions that combines flux-rope emergence, mass draining, near-surface reconnection, and the interaction with the surrounding field. Whether deterministic forecasting is in principle possible remains to be seen: to date no reliable such forecasts can be made. Large-sample studies based on long-duration, comprehensive observations of active regions from their emergence through their flaring phase are needed to help us better understand these complex phenomena.     

CME–flare association during the 23rd solar cycle

The relation between coronal mass ejections (CMEs) and solar flares are statistically studied. More than 10,000 CME events observed by SOHO/LASCO during the period 1996–2005 have been analyzed. The soft X-ray flux measurements provided by the Geostationary Operational Environmental Satellite (GOES), recorded more than 20,000 flares in the same time period. The data is filtered under certain temporal and spatial conditions to select the CME–flare associated events. The results show that CME–flare associated events are triggered with a lift-off time within the range 0.4–1.0 h. We list a set of 41 CME–flare associated events satisfying the temporal and spatial conditions. The listed events show a good correlation between the CME energy and the X-ray flux of the CME–flare associated events with correlation coefficient of 0.76.     

Properties and relationship between solar eruptive flares and Coronal Mass Ejections during rising phase of Solar Cycles 23 and 24

Statistical relationship between major flares and the associated CMEs during rising phases of Solar Cycles 23 and 24 are studied. Totally more than 6000 and 10,000 CMEs were observed by SOHO/LASCO (Solar and Heliospheric Observatory/Large Angle Spectrometric Coronagraph) during 23rd [May 1996–June 2002] and 24th [December 2008–December 2014] solar cycles, respectively. In particular, we studied the relationship between properties of flares and CMEs using the limb events (longitude 70–85°) to avoid projection effects of CMEs and partial occultation of flares that occurred near 90°. After selecting a sample of limb flares, we used certain spatial and temporal constraints to find the flare-CME pairs. Using these constraints, we compiled 129 events in Solar Cycle 23 and 92 events in Solar Cycle 24. We compared the flare-CME relationship in the two solar cycles and no significant differences are found between the two cycles. We only found out that the CME mean width was slightly larger and the CME mean acceleration was slightly higher in cycle 24, and that there was somewhat a better relation between flare flux and CME deceleration in cycle 24 than in cycle 23.     

X级质子耀斑的特征研究

为了更加准确地判断X级耀斑是否引发质子事件,对X级质子耀斑和非质子耀斑的耀斑积分通量、源区、CME速度、CME角宽度、背景太阳风速度及背景X射线通量的分布进行了统计研究.发现非质子耀斑和质子耀斑的积分通量、经度、CME速度和CME角宽度具有明显不同的分布.非质子耀斑大多集中在东部,耀斑积分通量小于0.3J·m-2,CME速度小于1300km·s-1的区域内;质子耀斑大多集中在中部或西部,耀斑积分通量大于0.3J·m-2,CME速度大于1300km·s-1的区域内.质子耀斑伴随的CME角宽度主要集中在360°,非质子耀斑的CME角宽度分布则相对分散.两类耀斑的背景太阳风速度和背景X射线通量分布差别不大.利用两类耀斑各个参量分布上的差异,有望提高X级耀斑预报的准确率.      

Investigating the Coronal Mass Ejections associated with DH type-II radio bursts and solar flares during the ascending phase of the solar cycle 24

We studied a set of 74 CMEs, with shedding the light on the halo-CMEs (HCMEs), that are associated with decametric – hectometric (DH) type-II radio bursts (1–16?MHz) and solar flares during the period 2008–2014. The events were classified into 3 groups (disk, intermediate, and limb events) based on their longitudinal distribution.We found that the events are mostly distributed around 15.32° and 15.97° at the northern and southern solar hemispheres, respectively. We found that there is a clear dependence between the longitude and the CME’s width, speed, acceleration, mass, and kinetic energy. For the CMEs’ widths, most of the events were HCMEs (～62%), while the partial HCMEs comprised ～35% and the rest of events were CMEs with widths less than 120°. For the CMEs’ speeds, masses, and kinetic energies, the mean values showed a direct proportionality with the longitude, in which the limb events had the highest speeds, the largest masses, and the highest kinetic energies. The mean peak flux of the solar flares for different longitudes was comparable, but the disk flares were more energetic. The intermediate flares were considered as gradual flares since they tended to last longer, while the limb flares were considered as impulsive flares since they tended to last shorter.A weak correlation (R?=?0.32) between the kinetic energy of the CMEs and the duration of the associated flares has been noticed, while there was a good correlation (R?=?0.76) between the kinetic energy of the CMEs and the peak flux of the associated flares. We found a fair correlation (R?=?0.58) between the kinetic energy of the CMEs and the duration of the associated DH type-II radio bursts.     

Homologous flare–CME events and their metric type II radio burst association

Active region NOAA 11158 produced many flares during its disk passage. At least two of these flares can be considered as homologous: the C6.6 flare at 06:51 UT and C9.4 flare at 12:41 UT on February 14, 2011. Both flares occurred at the same location (eastern edge of the active region) and have a similar decay of the GOES soft X-ray light curve. The associated coronal mass ejections (CMEs) were slow (334 and 337 km/s) and of similar apparent widths (43° and 44°), but they had different radio signatures. The second event was associated with a metric type II burst while the first one was not. The COR1 coronagraphs on board the STEREO spacecraft clearly show that the second CME propagated into the preceding CME that occurred 50 min before. These observations suggest that CME–CME interaction might be a key process in exciting the type II radio emission by slow CMEs.     

What are the physical mechanisms of eruptions and CMEs?

CMEs are due to physical phenomena that drive both, eruptions and flares in active regions. Eruptions/CMEs must be driven from initially force-free current-carrying magnetic field. Twisted flux ropes, sigmoids, current lanes and pattern in photospheric current maps show a clear evidence of currents parallel to the magnetic field. Eruptions occur starting from equilibria which have reached some instability threshold. Revisiting several data sets of CME observations we identified different mechanisms leading to this unstable state from a force free field. Boundary motions related to magnetic flux emergence and shearing favor the increase of coronal currents leading to the large flares of November 2003. On the other hand, we demonstrated by numerical simulations that magnetic flux emergence is not a sufficient condition for eruptions. Filament eruptions are interpreted either by a torus instability for an event occurring during the minimum of solar activity either by the diffusion of the magnetic flux reducing the tension of the restraining arcade. We concluded that CME models (tether cutting, break out, loss of equilibrium models) are based on these basic mechanisms for the onset of CMEs.     

Statistical study of twist values of transequatorial loops and the relationship with flares

In this paper, the twist values of ‘S’-shape transequatorial loops (TLs) from 1991 to 2001 are calculated, GOES soft X-ray flares dataset of the active regions connected by these TLs are investigated. The result shows the twist value of the TLs has a weak relation with the flare flux. There is no clear correlation between the twist value and the distance between the footpoint of TLs and location of flare in the corresponding active regions.     

CMEs and active regions on the sun

The relationship between active regions (ARs) and coronal mass ejections (CMEs) is studied. For this purpose a statistical analysis of 694 CMEs associated with ARs was carried out. We considered the relationship between properties of the CMEs and ARs characterized using the McIntosh classification. We demonstrated that CMEs are likely to be launched from ARs in the mature phase of their evolution when they have complex magnetic field. The fastest and halo CMEs can be ejected only from the most complex ARs (when an AR is a bipolar group of spots with large asymmetric penumbras around the main spot with many smaller spots in the group). We also showed that the wider events have a tendency to originate from uncomplicated magnetic structures. This tendency was used for estimation of the real angular widths of the halo CMEs. The probability of launching of fast CMEs increases together with increase of the complexity and size of ARs. The widest, but slow, CMEs originate from the simplest magnetic structure which are still able to produce CMEs. Our results could be useful for forecasting of space weather.     

Two energy release processes for CMEs: MHD catastrophe and magnetic reconnection

It remains an open question how magnetic energy is rapidly released in the solar corona so as to create solar explosions such as solar flares and coronal mass ejections (CMEs). Recent studies have confirmed that a system consisting of a flux rope embedded in a background field exhibits a catastrophic behavior, and the energy threshold at the catastrophic point may exceed the associated open field energy. The accumulated free energy in the corona is abruptly released when the catastrophe takes place, and it probably serves as the main means of energy release for CMEs at least in the initial phase. Such a release proceeds via an ideal MHD process in contrast with nonideal ones such as magnetic reconnection. The catastrophe results in a sudden formation of electric current sheets, which naturally provide proper sites for fast magnetic reconnection. The reconnection may be identified with a solar flare associated with the CME on one hand, and produces a further acceleration of the CME on the other. On this basis, several preliminary suggestions are made for future observational investigations, especially with the proposed Kuafa satellites, on the roles of the MHD catastrophe and magnetic reconnection in the magnetic energy release associated with CMEs and flares.     

Statistical study of radio drifting pulsation structures with associated CMEs and other observations

Solar radio burst, especially the fine structures (FSs) and the drifting pulsation structures (DPSs), may be used as an important diagnostics tool to draw the evolution map of the flare loop in the initial phase of solar flares. In this work, 52 radio events were found accompanying with DPSs. They were all observed with the Solar Radio Spectrometers (0.625–7.6 GHz) of China during 1998–2004. Combining the radio observations with LASCO-C2, Goes-8 SXR, H_α, EUV and Trace observations, we analyzed all these events and obtained some statistic conclusions: First, 88% DPSs take place at the initial phase of the radio burst, and their rich spectrum characteristics are helpful to understand the events further. Second, 83% DPSs are associated with CMEs or ejection events, and all the events are accompanied by Goes SXR flare. Third, for CMEs and DPSs, which take the first step, there is no significant predominance of either of them. The relationship between the DPSs and CMEs is still not clear in this study because of the lack of spatial resolution in the centimeter–decimeter band. However, the EIT or Trace ejection happened during the onset/end time of DPSs. They are signatures of the initial phase of CMEs. Two events will be illustrated to explain this.     

Kuafu and the studies of CME initiation

We first briefly review the current trend in the studies of coronal mass ejections (CMEs), then summarize some recent efforts in understanding the CME initiation. Emphasis has been put on the studies of Earth-directed CMEs whose associated surface activity and large scale magnetic source have been well identified. The data analysis by combining the MDI full disc magnetograms, vector magnetograms of active regions, EUV waves and dimmings, non-thermal radio sources, and the SOHO LASCO observations has shed new light in understanding the CME magnetism. However, the current studies seem to invoke new observations in a few aspects: (1) The observations which enable us to trace CMEs from the earliest associated surface activity to its initial acceleration and key development in the low corona in the height of 1–3 R; (2) The imaging spectroscopic observations which can be used to diagnose the early plasma outflow and the line-of-sight velocity in understanding the kinematics of CMEs; (3) The accurate timing from primary magnetic energy release, manifested by chromospheric activity, non-thermal radio bursts, and EUV, X-ray and γ-ray emissions, to the CME initiation, early acceleration and propagation, and the consequences in the interplanetary space and magnetosphere. The Kuafu Mission will meet the basic requirement for the new observations in CME initiation studies and serve as a monitor of space weather of the Sun–Earth system.     

Source investigation of impulsive He-rich particle events

We have investigated the source characteristic and coronal magnetic field structure of six impulsive solar energetic particle (SEP) events selected from Wang et al. [Wang, Y.-M., Pick, M., Mason, G.M. Coronal holes, jets, and the origin of ³He-rich particle events. ApJ 639, 495, 2006] and Pick et al. [Pick, M., Mason, G.M., Wang, Y.-M., Tan, C., Wang, L. Solar source regions for ³He-rich solar energetic particle events identified using imaging radio, optical, and energetic particle observations. ApJ 648, 1247, 2006]. Some results are obtained: first, 2 events are associated with wide (≈100°) CMEs (hereafter wide CME events), another 4 events are associated with narrow (?40°) CMEs (hereafter narrow CME events); second, the coronal magnetic field configuration of narrow CME events appear more simple than that of the wide CME events; third, the photospheric magnetic field evolutions of all these events show new emergence of fluxes, while one case also shows magnetic flux cancellation; fourth, the EUV jets usually occurred very close to the footpoint of the magnetic field loop, while meter type III bursts occurred near or at the top of the loop and higher than EUV jets. Furthermore, the heights of type III bursts are estimated from the result of the coronal magnetic field extrapolations.     

From solar nanoflares to stellar giant flares: Scaling laws and non-implications for coronal heating

In this study we explore physical scaling laws applied to solar nanoflares, microflares, and large flares, as well as to stellar giant flares. Solar flare phenomena exhibit a fractal volume scaling, V(L)  L^1.9, with L being the flare loop length scale, which explains the observed correlation between the total emission measure EM_p and flare peak temperature T_p in both solar and stellar flares. However, the detected stellar flares have higher emission measures EM_p than solar flares at the same flare peak temperature T_p, which can be explained by a higher electron density that is caused by shorter heating scale height ratios s_H/L ≈ 0.04–0.1. Using these scaling laws we calculate the total radiated flare energies E_X and thermal flare energies E_T and find that the total counts C are a good proxy for both parameters. Comparing the energies of solar and stellar flares we find that even the smallest observed stellar flares exceed the largest solar flares, and thus their observed frequency distributions are hypothetically affected by an upper cutoff caused by the maximum active region size limit. The powerlaw slopes fitted near the upper cutoff can then not reliably be extrapolated to the microflare regime to evaluate their contribution to coronal heating.