Flares before and after coronal mass ejections

Flare characteristics such as the flare occurrence number density and the distribution of peak flux as well as duration of flares occurring on either side of a coronal mass ejection（CME） onset time are studied. While the flares are rather evenly distributed statistically on either side of the CME onset time,the flare peak flux and duration tend to decrease depending upon their occurrence either before or after the CME onset. This is consistent with the earlier findings that flares emit higher energy before a CME whereas the energy is less in flares occurring after a CME.

Peak flux of flares associated with coronal mass ejections

Features of flares that occur in association with coronal mass ejections （CMEs） have often displayed variations compared to flares with no associated CMEs. A comparative estimation of peak flux values of flares associated with CMEs and those without CMEs is made. Peak flux values of flares associated with CMEs show distinctly higher values in comparison to flares with no associated CMEs. Higher peak flux of CME associated flares may be attributed to the heating of plasma to higher tempera- ture when associated with CMEs. While providing a distinct difference between the flux values of flares clearly associated with CMEs compared to flares associated with no CMEs, this study also highlights an evident difficulty in making distinct flare-CME associations.

Investigation of two coronal mass ejections from circular ribbon source region:Origin,Sun-Earth propagation and Geoeffectiveness

In this article,we compare the properties of two coronal mass ejections(CMEs)that show similar source region characteristics but different evolutionary behaviors in the later phases.We discuss the two events in terms of their near-Sun characteristics,interplanetary evolution and geoeffectiveness.We carefully analyzed the initiation and propagation parameters of these events to establish the precise CMEinterplanetary CME(ICME)connection and their near-Earth consequences.The first event is associated with poor geomagnetic storm disturbance index(Dst≈-20 n T)while the second event is associated with an intense geomagnetic storm of DST≈-119 n T.The configuration of the sunspots in the active regions and their evolution are observed by Helioseismic and Magnetic Imager(HMI).For source region imaging,we rely on data obtained from Atmospheric Imaging Assembly(AIA)on board Solar Dynamics Observatory(SDO)and Hαfiltergrams from the Solar Tower Telescope at Aryabhatta Research Institute of Observational Sciences(ARIES).For both the CMEs,flux rope eruptions from the source region triggered flares of similar intensities(≈M1).At the solar source region of the eruptions,we observed a circular ribbon flare(CRF)for both cases,suggesting fan-spine magnetic configuration in the active region corona.The multi-channel SDO observations confirm that the eruptive flares and subsequent CMEs were intimately related to the filament eruption.Within the Large Angle and Spectrometric Coronograph(LASCO)field of view(FOV)the two CMEs propagated with linear speeds of 671 and 631 km s-1,respectively.These CMEs were tracked up to the Earth by Solar Terrestrial Relations Observatory(STEREO)instruments.We find that the source region evolution of CMEs,guided by the large-scale coronal magnetic field configuration,along with near-Sun propagation characteristics,such as CME-CME interactions,played important roles in deciding the evolution of CMEs in the interplanetary medium and subsequently their geoeffectiveness.

Ensemble prediction model of solar proton events associated with solar flares and coronal mass ejections

An ensemble prediction model of solar proton events （SPEs）, combining the information of solar flares and coronal mass ejections （CMEs）, is built. In this model, solar flares are parameterized by the peak flux, the duration and the longitude. In addition, CMEs are parameterized by the width, the speed and the measurement position angle. The importance of each parameter for the occurrence of SPEs is estimated by the information gain ratio. We find that the CME width and speed are more informative than the flare’s peak flux and duration. As the physical mechanism of SPEs is not very clear, a hidden naive Bayes approach, which is a probability-based calculation method from the field of machine learning, is used to build the prediction model from the observational data. As is known, SPEs originate from solar flares and/or shock waves associated with CMEs. Hence, we first build two base prediction models using the properties of solar flares and CMEs, respectively. Then the outputs of these models are combined to generate the ensemble prediction model of SPEs. The ensemble prediction model incorporating the complementary information of solar flares and CMEs achieves better performance than each base prediction model taken separately.

The energetic relationship among geoeffective solar flares, associated CMEs and SEPs

Major solar eruptions （flares, coronal mass ejections （CMEs） and solar energetic particles （SEPs）） strongly influence geospace and space weather. Currently, the mechanism of their influence on space weather is not well understood and requires a detailed study of the energetic relationship among these eruptive phenomena. From this perspective, we investigate 30 flares （observed by RHESSI）, followed by weak to strong geomagnetic storms. Spectral analysis of these flares suggests a new power-law relationship （r - 0.79） between the hard X-ray （HXR） spectral index （before flarepeak） and linear speed of the associated CME observed by LASCO/SOHO. For 12 flares which were followed by SEP enhancement near Earth, HXR and SEP spectral analysis reveals a new scaling law （r - 0.9） between the hardest X-ray flare spectrum and the hardest SEP spectrum. Furthermore, a strong correlation is obtained between the linear speed of the CME and the hardest spectrum of the corresponding SEP event （r - 0.96）. We propose that the potentially geoeffective flare and associated CME and SEP are well-connected through a possible feedback mechanism, and should be regarded within the framework of a solar eruption. Owing to their space weather effects, these new results will help improve our current understanding of the Sun-Earth relationship, which is a major goal of research programs in heliophysics.

Associations of decimetric type Ⅲ bursts with coronal mass ejections and Hα flares

We present a statistical study of decimetric type Ⅲ radio bursts, coronal mass ejections （CMEs）, and Hα flares observed in the period from July 2000 to March 2005. In total, we investigated 395 decimetric type Ⅲ radio burst events, 21% of which showed apparent correlation to CMEs that were associated with Hα flares. We noticed that the Hα flares which were strongly associated with CMEs were gradual events, and 82% of them took place before CMEs appeared in the field of view of LASCO C2; that most of the CME-associated radio bursts started in the frequency range around 750 MHz with a frequency drifting rate of several hundred MHz s-1, of which both positive and negative ones were recognized; and that the correlation of type Ⅲ radio bursts to CMEs without associated flares is fairly vague, less than 9%.

Periodicity in the most violent solar eruptions: recent observations of coronal mass ejections and flares revisited

Using the Hilbert-Huang Transform method, we investigate the periodic- ity in the monthly occurrence numbers and monthly mean energy of coronal mass ejections （CMEs） observed by the Large Angle and Spectrometric Coronagraph Experiment on board the Solar and Heliographic Observatory from 1999 March to 2009 December. We also investigate the periodicity in the monthly occurrence numbers of Hα flares and monthly mean flare indices from 1996 January to 2008 December. The results show the following. （1） The period of 5.66 yr is found to be statistically significant in the monthly occurrence numbers of CMEs; the period of 10.5 yr is found to be statistically significant in the monthly mean energy of CMEs. （2） The periods of 3.05 and 8.70 yr are found to be statistically significant in the monthly occurrence numbers of Hα flares; the period of 9.14 yr is found to be statistically significant in the monthly mean flare indices.

A magnetic confinement nuclear fusion mechanism for solar flares

We propose a magnetic confinement nuclear fusion mechanism for the evolution of a solar flare in the solar atmosphere.The mechanism agrees with two observed characteristics of explosive flares and coronal mass ejections(CMEs) that have proved to be very difficult to explain with previous mechanisms:the huge enrichments of3 He and the high energy gamma ray radiation.The twisted magnetic flux rope is a typical structure during the solar flares,which is closely related to the solar active region that magnetic fields have almost complete control over the plasma.Consequently,the plasma inside the flux rope is heated to more than 1.0×107 K by an adiabatic compression process,and then the thermonuclear fusion can take place in the flux rope accompanied with high energy gamma rays.We utilize the time-dependent ideal 2.5-dimensional magnetohydrodynamic(MHD) simulation to demonstrate the physical mechanism for producing flares,which reveals three stages of flare development with the process of magnetic energy conversion and intense release during the solar flares and CMEs in the solar atmosphere.Furthermore,we discuss the relationship between magnetic reconnection and solar eruptions.

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 associated 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 correlated 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.

Dependence of large SEP events with different energies on the associated flares and CMEs

To investigate the dependence of large gradual solar energetic particle（SEP） events on the associated flares and coronal mass ejections（CMEs）, the correlation coefficients（CCs） between peak intensities of E 〉 10 MeV（I10）, E 〉 30 MeV（I30） and E 〉 50 MeV（I50） protons and soft X-ray（SXR） emission of associated flares and the speeds of associated CMEs in the three longitudinal areas W0–W39, W40–W70（hereafter the well connected region） and W71–W90 have been calculated.Classical correlation analysis shows that CCs between SXR emission and peak intensities of SEP events always reach their largest value in the well connected region and then decline dramatically in the longitudinal area outside the well connected region, suggesting that they may contribute to the production of SEPs in large SEP events. Both classical and partial correlation analyses show that SXR fluence is a better parameter describing the relationship between flares and SEP events. For large SEP events with source location in the well connected region, the CCs between SXR fluence and I10, I30 and I50 are0.58±0.12, 0.80±0.06 and 0.83±0.06 respectively, while the CCs between CME speed and I10, I30 and I50 are 0.56±0.12, 0.52±0.13 and 0.48±0.13 respectively. The partial correlation analyses show that in the well connected region, both CME shock and SXR fluence can significantly affect I10, but SXR peak flux makes no additional contribution. For E 〉 30 MeV protons with source location in the well connected region, only SXR fluence can significantly affect I30, and the CME shock makes a small contribution to I30, but SXR peak flux makes no additional contribution. For E 〉 50 MeV protons with source location in the well connected region, only SXR fluence can significantly affect I50, but both CME shock and SXR peak flux make no additional contribution. We conclude that these findings provide statistical evidence that for SEP events with source locations in the well connected region, a CME shock is only an effective accelerator for E 〈 30 MeV protons. However, flares are not only effective accelerators for E 〈 30 MeV protons, but also for E 〉 30 MeV protons, and E 〉 30 MeV protons may be mainly accelerated by concurrent flares.

Dependence of E ≥ 100 MeV protons on the associated flares and CMEs

To investigate the possible solar source of high-energy protons, correlation coefficients between the peak intensities of E ≥ 100 MeV protons, I100, and the peak flux and fluence of solar soft X-ray（SXR） emission, and coronal mass ejection（CME） linear speed in the three longitudinal areas W0-W39, W40-W70 and W71-W90 have been calculated respectively. Classical correlation analysis shows that the correlation coefficients between CME speeds and I100 in the three longitudinal areas are0.28±0.21, 0.35±0.21 and 0.04±0.30 respectively. The classical correlation coefficients between I100 and SXR peak flux in the three longitudinal areas are 0.48±0.17, 0.72±0.13 and 0.02±0.30 respectively, while the correlation coefficients between I100 and SXR fluence in the three longitudinal areas are 0.25±0.21, 0.84±0.07 and 0.10±0.30 respectively. Partial correlation analysis shows that for solar proton events with source location in the well connected region（W40-W70）, only SXR fluence can significantly affect the peak intensity of E ≥ 100 MeV protons, but SXR peak flux has little influence on the peak intensities of E ≥ 100 MeV protons; moreover, CME speed has no influence on the peak intensities of E ≥ 100 MeV protons. We conclude that these findings provide statistical evidence that E ≥ 100 MeV protons may be mainly accelerated by concurrent flares.

Space Weather – Sun Earth Relations

Sun, a star of spectral type G2 is the main source of energy to the Earth. Being close to the Earth, Sun pro-duces a resolvable disk of great detail, which is not possible for other stars. Solar flares and coronal mass ejections are the enigmatic phenomena that occur in the solar atmosphere and regularly bombard the Earth’s environment in addition to the solar wind. Thus it becomes important for us not only to understand these physical processes of the Sun, but in addition how these activities affect the Earth and it’s surrounding. Thus a branch of study called ‘Space Weather’ had emerged in the recent past, which connects the Sun Earth rela-tions. This paper details about the solar activity and associated energetic phenomena that occur in the atmosphere of the Sun and their influence on the Earth.

Possible Connections between X-Solar Flares and Worldwide Variation in Seismicity Enhancement

We developed a?statistical study analyzing global seismicity enhancement and its variation?overtwenty years.?X-flares sometimes occur in conjunction with Coronal Mass Ejections (CME),which make their connection with the Earth’s magnetosphere stronger.?The preliminary study divided the Earth into seven regions determined by longitude and latitude, and nine levels of depth valid for most locations?in the?Pacific area.?The results showed that X beams influenced seismicity in terrestrial localities, mainly high magnitude earthquakes occurring below the crust at 70 km.?These internal enhancements happen without the presence of any external forces such as studied in Solar Speed Winds.?Nevertheless, those variations are perceptible in the presence of intense X flares and CME and less observed in the periods during which flares were absent. Two cases of high magnitude earthquakes in recent?years are analyzed, and the extreme external conditions of those events fit?with this theory.

The Relationship between Magnetic Gradient and Magnetic Shear in Five Super Active Regions Producing Great Flares

We study the magnetic structure of five well-known active regions that produced great flares （X5 or larger）. The six flares under investigation are the X12 flare on 1991 June 9 in AR 6659, the X5.7 flare on 2000 July 14 in AR 9077, the X5.6 flare on 2001 April 6 in AR 9415, the X5.3 flare on 2001 August 25 in AR 9591, the X17 flare on 2003 October 28 and the X10 flare on 2003 October 29, both in AR 10486. The last five events had corresponding LASCO observations and were all associated with Halo CMEs. We analyzed vector magnetograms from Big Bear Solar Observatory, Huairou Solar Observing Station, Marshall Space Flight Center and Mees Solar Observatory. In particular, we studied the magnetic gradient derived from line-of-sight magnetograms and magnetic shear derived from vector magnetograms, and found an apparent correlation between these two parameters at a level of about 90%. We found that the magnetic gradient could be a better proxy than the shear for predicting where a major flare might occur： all six flares occurred in neutral lines with maximum gradient. The mean gradient of the flaring neutral lines ranges from 0.14 to 0.50 G km^-1, 2.3 to 8 times the average value for all the neutral lines in the active regions. If we use magnetic shear as the proxy, the flaring neutral line in at least one, possibly two, of the six events would be mis-identified.

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.

Proton activity of the Sun in current solar cycle 24

We present a study of seven large solar proton events in the current solar cycle 24（from 2009 January up to the current date）. They were recorded by the GOES spacecraft with the highest proton fluxes being over 200 pfu for energies 〉10 Me V. In situ particle measurements show that：（1） The profiles of the proton fluxes are highly dependent on the locations of their solar sources, namely flares or coronal mass ejections（CMEs）, which confirms the ＂heliolongitude rules＂ associated with solar energetic particle fluxes;（2） The solar particle release（SPR） times fall in the decay phase of the flare emission, and are in accordance with the times when the CMEs travel to an average height of 7.9 solar radii; and（3） The time differences between the SPR and the flare peak are also dependent on the locations of the solar active regions. The results tend to support the scenario of proton acceleration by the CME-driven shock,even though there exists a possibility of particle acceleration at the flare site, with subsequent perpendicular diffusion of accelerated particles in the interplanetary magnetic field. We derive the integral time-of-maximum spectra of solar protons in two forms： a single power-law distribution and a power law roll-over with an exponential tail. It is found that the unique ground level enhancement that occurred in the event on 2012 May 17 displays the hardest spectrum and the largest roll-over energy which may explain why this event could extend to relativistic energies.

Comparison between the eruptive X2.2 flare on 2011 February15 and confined X3.1 flare on 2014 October 24

We compare two contrasting X-class flares in terms of magnetic free energy, relative magnetic helicity and decay index of the active regions （ARs） in which they occurred. The events in question are the eruptive X2.2 flare from AR 11158 accompanied by a halo coronal mass ejection （CME） and the confined X3.1 flare from AR 12192 with no associated CME. These two flares exhibit similar behavior of free magnetic energy and helicity buildup for a few days preceding them. A major difference between the two flares is found to lie in the time-dependent change of magnetic helicity of the ARs that hosted them. AR 11158 shows a significant decrease in magnetic helicity starting -4 hours prior to the flare, but no apparent decrease in helicity is observed in AR 12192. By examining the magnetic helicity injection rates in terms of sign, we confirmed that the drastic decrease in magnetic helicity before the eruptive X2.2 flare was not caused by the injection of reversed helicity through the photosphere but rather the CME-related change in the coronal magnetic field. Another major difference we find is that AR 11158 had a significantly larger decay index and therefore weaker overlying field than AR 12192. These results suggest that the coronal magnetic helicity and the decay index of the overlying field can provide a clue about the occurrence of CMEs.

Kinematics and amplitude evolution of global coronal extreme ultraviolet waves

With the observations of the Solar-Terrestrial Relations Observatory （STEREO） and the Solar Dynamics Observatory （SDO）, we analyze in detail the kine- matics of global coronal waves together with their intensity amplitudes （so-called ＂perturbation profiles＂）. We use a semi-automatic method to investigate the pertur- bation profiles of coronal waves. The location and amplitude of the coronal waves are calculated over a 30~ sector on the sphere, where the wave signal is strongest. The position with the strongest perturbation at each time is considered as the location of the wave front. In all four events, the wave velocities vary with time for most of their lifetime, up to 15 rain, while in the event observed by the Atmospheric Imaging Assembly there is at, additional early phase with a much higher velocity. The velocity varies greatly between different waves from 216 to 440 km s-1. The velocity of the two waves initially increases, subsequently decreases, and then increases again. Two other waves show a deceleration followed by an acceleration. Three categories of am- plitude evolution of global coronal waves are found for the four events. The first is that the amplitude only shows a decrease. The second is that the amplitude initially increases and then decreases, and the third is that the amplitude shows an orderly in- crease, a decrease, an increase again and then a decrease. All the extreme ultraviolet waves show a decrease in amplitude while propagating farther away, probably because the driver of the global coronal wave （coronal mass ejection） is moving farther away from the solar surface.

Magnetic interactions during sympathetic solar eruptions

We present the first evidence for occurrences of magnetic interactions between a jet, a filament and coronal loops during a complex event, in which two flares sequentially occurred at different positions of the same active region and were closely associated with two successive coronal mass ejections （CMEs）, respectively. The coronal loops were located outside but nearby the filament channel before the flares. The jet, originating from the first flare during its rise phase, not only hit the filament body but also met one of the ends of the loops. The filament then underwent an inclined eruption followed by the second flare and met the same loop end once more. Both the jet and the filament eruption were accompanied by the development of loop disturbances and the appearances of brightenings around the meeting site. In particular, the erupting filament showed clear manifestations of interactions with the loops. After a short holdup, only its portion passed through this site, while the other portion remained at the same place. Following the filament eruption and the loop disappearance, four dimmings were formed and located near their four ends. This is a situation that we define as ＂quadrupolar dimmings.＂ It appears that the two flares consisted of a sympathetic pair physically linked by the interaction between the jet and the filament, and their sympathy indicated that of the two CMEs. Moreover, it is very likely that the two sympathetic CMEs were simultaneously associated with the disappearing loops and the quadrupole dimmings.

Magnetic flux ropes in the solar corona: structure and evolution toward eruption

Magnetic flux ropes are characterized by coherently twisted magnetic field lines,which are ubiquitous in magnetized plasmas.As the core structure of various eruptive phenomena in the solar atmosphere,flux ropes hold the key to understanding the physical mechanisms of solar eruptions,which impact the heliosphere and planetary atmospheres.The strongest disturbances in the Earth’s space environments are often associated with large-scale flux ropes from the Sun colliding with the Earth’s magnetosphere,leading to adverse,sometimes catastrophic,space-weather effects.However,it remains elusive as to how a flux rope forms and evolves toward eruption,and how it is structured and embedded in the ambient field.The present paper addresses these important questions by reviewing current understandings of coronal flux ropes from an observer’s perspective,with an emphasis on their structures and nascent evolution toward solar eruptions,as achieved by combining observations of both remote sensing and in-situ detection with modeling and simulation.This paper highlights an initiation mechanism for coronal mass ejections(CMEs)in which plasmoids in current sheets coalesce into a’seed’flux rope whose subsequent evolution into a CME is consistent with the standard model,thereby bridging the gap between microscale and macroscale dynamics.