Photospheric Magnetic Evolution in the WHI Active Regions

Sequences of line-of-sight (LOS) magnetograms recorded by the Michelson Doppler Imager are used to quantitatively characterize photospheric magnetic structure and evolution in three active regions that rotated across the Sun??s disk during the Whole Heliosphere Interval (WHI), in an attempt to relate the photospheric magnetic properties of these active regions to flares and coronal mass ejections (CMEs). Several approaches are used in our analysis, on scales ranging from whole active regions, to magnetic features, to supergranular scales, and, finally, to individual pixels. We calculated several parameterizations of magnetic structure and evolution that have previously been associated with flare and CME activity, including total unsigned magnetic flux, magnetic flux near polarity-inversion lines, amount of canceled flux, the ??proxy Poynting flux,?? and helicity flux. To catalog flare events, we used flare lists derived from both GOES and RHESSI observations. By most such measures, AR 10988 should have been the most flare- and CME-productive active region, and AR 10989 the least. Observations, however, were not consistent with this expectation: ARs 10988 and 10989 produced similar numbers of flares, and AR 10989 also produced a few CMEs. These results highlight present limitations of statistics-based flare and CME forecasting tools that rely upon line-of-sight photospheric magnetic data alone.     

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.     

Connecting Coronal Mass Ejections to Their Solar Active Region Sources: Combining Results from the HELCATS and FLARECAST Projects

Coronal mass ejections (CMEs) and other solar eruptive phenomena can be physically linked by combining data from a multitude of ground-based and space-based instruments alongside models; however, this can be challenging for automated operational systems. The EU Framework Package 7 HELCATS project provides catalogues of CME observations and properties from the Heliospheric Imagers on board the two NASA/STEREO spacecraft in order to track the evolution of CMEs in the inner heliosphere. From the main HICAT catalogue of over 2,000 CME detections, an automated algorithm has been developed to connect the CMEs observed by STEREO to any corresponding solar flares and active-region (AR) sources on the solar surface. CME kinematic properties, such as speed and angular width, are compared with AR magnetic field properties, such as magnetic flux, area, and neutral line characteristics. The resulting LOWCAT catalogue is also compared to the extensive AR property database created by the EU Horizon 2020 FLARECAST project, which provides more complex magnetic field parameters derived from vector magnetograms. Initial statistical analysis has been undertaken on the new data to provide insight into the link between flare and CME events, and characteristics of eruptive ARs. Warning thresholds determined from analysis of the evolution of these parameters is shown to be a useful output for operational space weather purposes. Parameters of particular interest for further analysis include total unsigned flux, vertical current, and current helicity. The automated method developed to create the LOWCAT catalogue may also be useful for future efforts to develop operational CME forecasting.     

Relation of CME Speed and Magnetic Helicity in CME Source Regions on the Sun during the Early Phase of Solar Cycles 23 and 24

To investigate the relations between coronal mass ejection (CME) speed and magnetic field properties measured in the photospheric surface of CME source regions, we selected 22 disk CMEs in the rising and early maximum phases of the current Solar Cycle 24. For the CME speed, we used two-dimensional (2D) projected speed observed by the Large Angle and Spectroscopic Coronagraph onboard the Solar and Heliospheric Observatory (SOHO/LASCO), as well as a 3D speed calculated from the triangulation method using multi-point observations. Two magnetic parameters of CME source regions were considered: the average of magnetic helicity injection rate and the total unsigned magnetic flux. We then classified the selected CMEs into two groups, showing: i) a monotonically increasing pattern with one sign of helicity (group A: 16 CMEs) and ii) a pattern of significant helicity injection followed by its sign reversal (group B: 6 CMEs). We found that: 1) 3D speed generally shows better correlations with the magnetic parameters than the 2D speed for 22 CME events in Solar Cycle 24; 2) 2D speed and the magnetic parameters of 22 CME events in this solar cycle have lower values than those of 47 CME events in Solar Cycle 23; 3) all events of group B in Solar Cycle 24 occur only after the beginning of the maximum phase, a trend well consistent with that shown in Solar Cycle 23; 4) the 2D speed and the helicity parameter of group B events continue to increase in the declining phase of Solar Cycle 23, while those of group A events abruptly decrease in the same period. Our results indicate that the two CME groups have a different tendency in the solar cycle variations of CME speed and the helicity parameters. Active regions that show a complex helicity evolution pattern tend to appear in the maximum and declining phases, while active regions with a relatively simple helicity evolution pattern appear throughout the whole solar cycle.     

Comparison of Helicity Signs in Interplanetary CMEs and Their Solar Source Regions

If all coronal mass ejections (CMEs) have flux ropes, then the CMEs should keep their helicity signs from the Sun to the Earth according to the helicity conservation principle. This study presents an attempt to answer the question from the Coordinated Data Analysis Workshop (CDAW), “Do all CMEs have flux ropes?”, by using a qualitative helicity sign comparison between interplanetary CMEs (ICMEs) and their CME source regions. For this, we select 34 CME–ICME pairs whose source active regions (ARs) have continuous SOHO/MDI magnetogram data covering more than 24 hr without data gap during the passage of the ARs near the solar disk center. The helicity signs in the ARs are determined by estimation of cumulative magnetic helicity injected through the photosphere in the entire source ARs. The helicity signs in the ICMEs are estimated by applying the cylinder model developed by Marubashi (Adv. Space. Res., 26, 55, 2000) to 16 second resolution magnetic field data from the MAG instrument onboard the ACE spacecraft. It is found that 30 out of 34 events (88 %) are helicity sign-consistent events, while four events (12 %) are sign-inconsistent. Through a detailed investigation of the source ARs of the four sign-inconsistent events, we find that those events can be explained by the local helicity sign opposite to that of the entire AR helicity (28 July 2000 ICME), incorrectly reported solar source region in the CDAW list (20 May 2005 ICME), or the helicity sign of the pre-existing coronal magnetic field (13 October 2000 and 20 November 2003 ICMEs). We conclude that the helicity signs of the ICMEs are quite consistent with those of the injected helicities in the AR regions from where the CMEs erupted.     

Numerical simulations of fast and slow coronal mass ejections

Solar coronal mass ejections (CMEs) show a large variety in their kinematic properties. CMEs originating in active regions and accompanied by strong flares are usually faster and accelerated more impulsively than CMEs associated with filament eruptions outside active regions and weak flares. It has been proposed more than two decades ago that there are two separate types of CMEs, fast (impulsive) CMEs and slow (gradual) CMEs. However, this concept may not be valid, since the large data sets acquired in recent years do not show two distinct peaks in the CME velocity distribution and reveal that both fast and slow CMEs can be accompanied by both weak and strong flares. We present numerical simulations which confirm our earlier analytical result that a flux‐rope CME model permits describing fast and slow CMEs in a unified manner. We consider a force‐free coronal magnetic flux rope embedded in the potential field of model bipolar and quadrupolar active regions. The eruption is driven by the torus instability which occurs if the field overlying the flux rope decreases sufficiently rapidly with height. The acceleration profile depends on the steepness of this field decrease, corresponding to fast CMEs for rapid decrease, as is typical of active regions, and to slow CMEs for gentle decrease, as is typical of the quiet Sun. Complex (quadrupolar) active regions lead to the fastest CMEs. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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.     

A Helicity-Based Method to Infer the CME Magnetic Field Magnitude in Sun and Geospace: Generalization and Extension to Sun-Like and M-Dwarf Stars and Implications for Exoplanet Habitability

Patsourakos et al. (Astrophys. J. 817, 14, 2016) and Patsourakos and Georgoulis (Astron. Astrophys. 595, A121, 2016) introduced a method to infer the axial magnetic field in flux-rope coronal mass ejections (CMEs) in the solar corona and farther away in the interplanetary medium. The method, based on the conservation principle of magnetic helicity, uses the relative magnetic helicity of the solar source region as input estimates, along with the radius and length of the corresponding CME flux rope. The method was initially applied to cylindrical force-free flux ropes, with encouraging results. We hereby extend our framework along two distinct lines. First, we generalize our formalism to several possible flux-rope configurations (linear and nonlinear force-free, non-force-free, spheromak, and torus) to investigate the dependence of the resulting CME axial magnetic field on input parameters and the employed flux-rope configuration. Second, we generalize our framework to both Sun-like and active M-dwarf stars hosting superflares. In a qualitative sense, we find that Earth may not experience severe atmosphere-eroding magnetospheric compression even for eruptive solar superflares with energies \({\approx}\, 10^{4}\) times higher than those of the largest Geostationary Operational Environmental Satellite (GOES) X-class flares currently observed. In addition, the two recently discovered exoplanets with the highest Earth-similarity index, Kepler 438b and Proxima b, seem to lie in the prohibitive zone of atmospheric erosion due to interplanetary CMEs (ICMEs), except when they possess planetary magnetic fields that are much higher than that of Earth.     

The source regions of solar coronal mass ejections

Knowledge of the origin of the solar coronal mass ejection (CME) may be crucial to our understanding of several active solar phenomena, such as flares, as well as to the structure and stability of the corona and the prediction of interplanetary disturbances. In recent years, two camps of opinion have emerged, based on the belief that CMEs either commonly originate from structures intimately linked to active regions or they originate from coronal hole regions. This present study investigates the locations of 95 CME events observed during 1984–1986 relative to coronal hole and active region features. We find no evidence to support the coronal hole hypothesis and many indications that active regions are indeed associated with the source regions of CMEs.     

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.     

Hemispheric Distribution of Subsurface Kinetic Helicity and Its Variation with Magnetic Activity

We study the hemispheric distribution of the kinetic helicity of subsurface flows in the near-surface layers of the solar convection zone and its variation with magnetic activity. We determine subsurface flows with a ring-diagram analysis applied to Global Oscillation Network Group (GONG) Dopplergrams and Dynamics Program data from the Michelson Doppler Imager (MDI) instrument onboard the Solar and Heliospheric Observatory (SOHO). We determine the average kinetic helicity density as a function of Carrington rotation and latitude. The average kinetic helicity density at all depths and the kinetic helicity, integrated over 2?–?7 Mm, follow the same hemispheric rule as the current/magnetic helicity proxies with predominantly positive values in the southern and negative ones in the northern hemisphere. This holds true for all levels of magnetic activity from quiet to active regions. However, this is a statistical result; only about 55 % of all locations follow the hemispheric rule. But these locations have larger helicity values than those that do not follow the rule. The average values of helicity density increase with depth for all levels of activity, which might reflect an increase of the characteristic size of convective motions with greater depth. The average helicity of subsets of high magnetic activity is about five times larger than that of subsets of low activity. The solar-cycle variation of helicity is thus mainly due to the presence or absence of active regions. During the rising phase of cycle 24, locations of high magnetic activity at low latitudes show a weaker hemispheric behavior compared to the rising phase of cycle 23.     

Magnetic source regions of coronal mass ejections

The majority of flare activity arises in active regions which contain sunspots, while Coronal Mass Ejection (CME) activity can also originate from decaying active regions and even so-called quiet solar regions which contain a filament. Two classes of CME, namely flare-related CME events and CMEs associated with filament eruption are well reflected in the evolution of active regions. The presence of significant magnetic stresses in the source region is a necessary condition for CME. In young active regions magnetic stresses are increased mainly by twisted magnetic flux emergence and the resulting magnetic footpoint motions. In old, decayed active regions twist can be redistributed through cancellation events. All the CMEs are, nevertheless, caused by loss of equilibrium of the magnetic structure. With observational examples we show that the association of CME, flare and filament eruption depends on the characteristics of the source regions:

?the strength of the magnetic field, the amount of possible free energy storage,

?the small- and large-scale magnetic topology of the source region as well as its evolution (new flux emergence, photospheric motions, cancelling flux), and

?the mass loading of the configuration (effect of gravity). These examples are discussed in the framework of theoretical models.

     

A Study of Connections Between Solar Flares and Subsurface Flow Fields of Active Regions

We investigate the connections between the occurrence of major solar flares and subsurface dynamic properties of active regions. For this analysis, we select five active regions that produced a total of 11 flares with peak X-ray flux intensity higher than M5.0. The subsurface velocity fields are obtained from time–distance helioseismology analysis using SDO/HMI (Solar Dynamics Observatory/Helioseismic and Magnetic Imager) Doppler observations, and the X-ray flux intensity is taken from GOES (Geostationary Operational Environmental Satellites). It is found that among the eight amplitude bumps in the evolutionary curves of subsurface kinetic helicity, five (62.5%) of them had a flare stronger than M5.0 occurring within 8 hours, either before or after the bumps. Another subsurface parameter is the Normalized Helicity Gradient Variance (NHGV), reflecting kinetic helicity spread in different depth layers; it also shows bumps near the occurrence of these solar flares. Although there is no one-to-one correspondence between the flare and the subsurface properties, these observational phenomena are worth further studies to better understand the flares’ subsurface roots, and to investigate whether the subsurface properties can be used for major flare forecasts.     

Active Regions with Superpenumbral Whirls and Their Subsurface Kinetic Helicity

We search for a signature of helicity flow from the solar interior to the photosphere and chromosphere. For this purpose, we study two active regions, NOAA 11084 and 11092, that show a regular pattern of superpenumbral whirls in chromospheric and coronal images. These two regions are good candidates for comparing magnetic/current helicity with subsurface kinetic helicity because the patterns persist throughout the disk passage of both regions. We use photospheric vector magnetograms from SOLIS/VSM and SDO/HMI to determine a magnetic helicity proxy, the spatially averaged signed shear angle (SASSA). The SASSA parameter produces consistent results leading to positive values for NOAA 11084 and negative ones for NOAA 11092 consistent with the clockwise and counter-clockwise orientation of the whirls. We then derive the properties of the subsurface flows associated with these active regions. We measure subsurface flows using a ring-diagram analysis of GONG high-resolution Doppler data and derive their kinetic helicity, h _z . Since the patterns persist throughout the disk passage, we analyze synoptic maps of the subsurface kinetic helicity density. The sign of the subsurface kinetic helicity is negative for NOAA 11084 and positive for NOAA 11092; the sign of the kinetic helicity is thus anticorrelated with that of the SASSA parameter. As a control experiment, we study the subsurface flows of six active regions without a persistent whirl pattern. Four of the six regions show a mixture of positive and negative kinetic helicity resulting in small average values, while two regions are clearly dominated by kinetic helicity of one sign or the other, as in the case of regions with whirls. The regions without whirls follow overall the same hemispheric rule in their kinetic helicity as in their current helicity with positive values in the southern and negative values in the northern hemisphere.     

How are Emerging Flux,Flares and CMEs Related to Magnetic Polarity Imbalance in Midi Data?

In order to understand whether major flares or coronal mass ejections (CMEs) can be related to changes in the longitudinal photospheric magnetic field, we study 4 young active regions during seven days of their disk passage. This time period precludes any biases which may be introduced in studies that look at the field evolution during the short-term flare or CME period only. Data from the Michelson Doppler Imager (MDI) with a time cadence of 96 min are used. Corrections are made to the data to account for area foreshortening and angle between line of sight and field direction, and also the underestimation of the flux densities. We make a systematic study of the evolution of the longitudinal magnetic field, and analyze flare and CME occurrence in the magnetic evolution. We find that the majority of CMEs and flares occur during or after new flux emergence. The flux in all four active regions is observed to have deviations from polarity balance both on the long term (solar rotation) and on the short term (few hours). The long-term imbalance is not due to linkage outside the active region; it is primarily related to the east–west distance from central meridian, with the sign of polarity closer to the limb dominating. The sequence of short-term imbalances are not closely linked to CMEs and flares and no permanent imbalance remains after them. We propose that both kinds of imbalance are due to the presence of a horizontal field component (parallel to the photospheric surface) in the emerging flux.     

A Numerical Study of the Response of the Coronal Magnetic Field to Flux Emergence

Large-scale solar eruptions, known as coronal mass ejections (CMEs), are regarded as the main drivers of space weather. The exact trigger mechanism of these violent events is still not completely clear; however, the solar magnetic field indisputably plays a crucial role in the onset of CMEs. The strength and morphology of the solar magnetic field are expected to have a decisive effect on CME properties, such as size and speed. This study aims to investigate the evolution of a magnetic configuration when driven by the emergence of new magnetic flux in order to get a better insight into the onset of CMEs and their magnetic structure. The three-dimensional, time-dependent equations for ideal magnetohydrodynamics are numerically solved on a spherical mesh. New flux emergence in a bipolar active region causes destabilisation of the initial stationary structure, finally resulting in an eruption. The initial magnetic topology is suitable for the ??breakout?? CME scenario to work. Although no magnetic flux rope structure is present in the initial condition, highly twisted magnetic field lines are formed during the evolution of the system as a result of internal reconnection due to the interaction of the active region magnetic field with the ambient field. The magnetic energy built up in the system and the final speed of the CME depend on the strength of the overlying magnetic field, the flux emergence rate, and the total amount of emerged flux. The interaction with the global coronal field makes the eruption a large-scale event, involving distant parts of the solar surface.     

Determining the Intrinsic CME Flux Rope Type Using Remote-sensing Solar Disk Observations

A key aim in space weather research is to be able to use remote-sensing observations of the solar atmosphere to extend the lead time of predicting the geoeffectiveness of a coronal mass ejection (CME). In order to achieve this, the magnetic structure of the CME as it leaves the Sun must be known. In this article we address this issue by developing a method to determine the intrinsic flux rope type of a CME solely from solar disk observations. We use several well-known proxies for the magnetic helicity sign, the axis orientation, and the axial magnetic field direction to predict the magnetic structure of the interplanetary flux rope. We present two case studies: the 2 June 2011 and the 14 June 2012 CMEs. Both of these events erupted from an active region, and despite having clear in situ counterparts, their eruption characteristics were relatively complex. The first event was associated with an active region filament that erupted in two stages, while for the other event the eruption originated from a relatively high coronal altitude and the source region did not feature a filament. Our magnetic helicity sign proxies include the analysis of magnetic tongues, soft X-ray and/or extreme-ultraviolet sigmoids, coronal arcade skew, filament emission and absorption threads, and filament rotation. Since the inclination of the post-eruption arcades was not clear, we use the tilt of the polarity inversion line to determine the flux rope axis orientation and coronal dimmings to determine the flux rope footpoints, and therefore, the direction of the axial magnetic field. The comparison of the estimated intrinsic flux rope structure to in situ observations at the Lagrangian point L1 indicated a good agreement with the predictions. Our results highlight the flux rope type determination techniques that are particularly useful for active region eruptions, where most geoeffective CMEs originate.     

晕状日冕物质抛射

主要介绍晕状日冕物质抛射（halo CMEs)的产生机制，包括向量磁场演化是怎样触发halo CMEa的：halo CME与耀斑，暗条活动的相互关系怎样，是否有规律可循，暗条爆发，耀斑等活动现象是如何相互联系的，halo CME事件是由一个活动区域或一个活动事件驱动物，还是多个活动区或多个活动事件相互作用的结果，给出两个halo CME的日面起源的观测例证，提出相反极笥的磁场对消是CME日面源区磁场演化的主要特征。