Erratum to: Geo-Effectiveness of Halo CMEs Based on Magnetic Parameters of the Solar Active Region

Solar active region magnetic parameters and their relationship with the properties of halo coronal mass ejections

Large solar energetic particles (SEPs) can cause adverse space weather hazards to human technology, and such events are especially associated with halo coronal mass ejections (CMEs). But in turn, a significant portion of halo CMEs are not associated with large SEPs. The objective of this study is to gain an understanding of the source region distinctions between halo CMEs in SEP and non-SEP events. Among the 176 halo CMEs observed from 2010 to 2024, we screen out 45 large SEP events and 131 non-SEP events from this data set. It is revealed that CME speed is a good discriminator between SEP and non-SEP events. Through classifying the source regions of all the halo CMEs, we find that 53% of SEP events originate from “single AR (active region),” and 47% from “multiple ARs” or “outside of ARs.” The corresponding proportion for non-SEP events is 70% and 30%. This suggests that SEP source regions are more likely to originate from large-scale sources. We have also calculated the relevant magnetic parameters of the source regions and found that SEP source regions have higher magnetic free energy and reconnection flux compared to non-SEP source regions. However, SEP source regions are smaller in terms of the intensive magnetic parameters such as mean characteristic magnetic twist α and mean shear angles. Our statistical results can provide new potential variables for forecasting SEPs.

We report on the properties of halo coronal mass ejections (HCMEs) in solar cycles 23 and 24. We compare the HCME properties between the corresponding phases (rise, maximum, and declining) in cycles 23 and 24 and compare those between the whole cycles. Despite the significant decline in the sunspot number (SSN) in cycle 24, which dropped by 46% with respect to cycle 23, the abundance of HCMEs is similar in the two cycles. The HCME rate per SSN is 44% higher in cycle 24. In the maximum phase, cycle 24 rate normalized to SSN increased by 127%, while the SSN dropped by 43%. The source longitudes of cycle 24 HCMEs are more uniformly distributed than those in cycle 23. We found that the average sky-plane speed in cycle 23 is ∼16% higher than that in cycle 24. The size distributions of the associated flares between the two cycles and the corresponding phases are similar. The average speed at a central meridian distance (CMD) ≥ 600 for cycle 23 is ∼28% higher than that of cycle 24. We discuss the unusual bump in HCME activity in the declining phase of cycle 23 as being due to exceptional active regions that produced many CMEs during 2003 October–2005 October. The differing HCME properties in the two cycles can be attributed to the anomalous expansion of cycle 24 CMEs. Considering the HCMEs in the rise, maximum, and declining phases, we find that the maximum phase shows the highest contrast between the two cycles.

We present a transformer model, named DeepHalo, to predict the occurrence of halo coronal mass ejections (CMEs). Our model takes as input an active region (AR) and a profile, where the profile contains a time series of data samples in the AR that are collected 24 hr before the beginning of a day, and predicts whether the AR would produce a halo CME during that day. Each data sample contains physical parameters, or features, derived from photospheric vector magnetic field data taken by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory. We survey and match CME events in the Space Weather Database Of Notification, Knowledge, Information and the Large Angle and Spectrometric Coronagraph CME Catalog, and we compile a list of CMEs, including halo CMEs and nonhalo CMEs, associated with ARs in the period between 2010 November and 2023 August. We use the information gathered above to build the labels (positive vs. negative) of the data samples and profiles at hand, where the labels are needed for machine learning. Experimental results show that DeepHalo with a true skill statistic (TSS) score of 0.907 outperforms a closely related long short-term memory network with a TSS score of 0.821. To our knowledge, this is the first time that the transformer model has been used for halo CME prediction.

In the first half of May 2024, the solar active region (AR) NOAA 13664 was responsible for generating the strongest geomagnetic storm in over 20 years through an enhanced production of coronal mass ejections (CMEs). A key factor in this production was the complex magnetic topology of AR13664. In this work, we investigate the region's magnetic topology related to the production of its first halo CME on May 8th. This is achieved by combining different observations of magnetic topology based on photospheric magnetic helicity and winding signatures and nonlinear force‐free field extrapolations, together with Atmospheric Imaging Assembly observations at different wavelengths. We present evidence that the first halo CME, and its associated X1.0 flare, was created by an emerging twisted flux tube within AR13664, following the general picture of the standard flare model. The coincidence of the first large magnetic winding signature with the start time of the X1.0 flare provides the onset time for the CME as well as the period of enhanced eruptive activity of the region—04:36 UT on May 8th.

To better understand the trigger mechanism of a coronal mass ejection (CME), we present the evolution of a CME source region (active region NOAA 12790) and the formation of a hot channel before the occurrence of the first halo CME in solar cycle 25. Through analyzing the evolution of Solar Dynamics Observatory/Helioseismic and Magnetic Imager line-of-sight magnetograms, it is found that continuous magnetic cancellation occurs at the polarity inversion line (PIL) in this active region. With ongoing magnetic cancellation, several bidirectional jets and unidirectional jets occur along the large-scale arched magnetic loops. A hot channel forms during the first bidirectional jet. After the occurrence of the fourth bidirectional jet, the hot channel immediately erupts and produces a C-class flare, a cusp structure, and a halo CME. It is worth pointing out that the cusp structure only appears in the 131 Å and 94 Å observations (temperature about 10 MK). The obvious contraction of the newly formed loops is observed at the top of the cusp structure. The observations reveal a clear physics process: magnetic cancellation of a bipolar magnetic field at the PIL results in the occurrence of the bidirectional/unidirectional jets and the formation of the hot channel. The axial magnetic flux feeding for the hot channel through the continued magnetic cancellation leads to the hot channel eruption, which results in the formation of the hot cusp structure and the occurrence of the C-class flare and the halo CME.

CMEs and active regions on the sun

In this article, we study the origin of precursor flare activity and investigate its role towards triggering the eruption of a flux rope which resulted into a dual-peak M-class flare (SOL2015-06-21T02:36) in the active region NOAA 12371. The flare evolved in two distinct phases with peak flux levels of M2.1 and M2.6 at an interval of $\approx$54 min. The active region exhibited striking moving magnetic features (MMFs) along with sunspot rotation. Non-linear force free field (NLFFF) modelling of the active region corona reveals a magnetic flux rope along the polarity inversion line in the trailing sunspot group which is observationally manifested by the co-spatial structures of an active region filament and a hot channel identified in the 304 and 94 \AA\ images, respectively, from the Atmospheric Imaging Assembly (AIA). The active region underwent a prolonged phase of flux enhancement followed by a relatively shorter period of flux cancellation prior to the onset of the flare which led to the build up and activation of the flux rope. Extreme ultra-violet (EUV) images reveal localised and structured pre-flare emission, from the region of MMFs, adjacent to the location of the main flare. Our analysis reveals strong, localised regions of photospheric currents of opposite polarities at the precursor location, thereby making the region susceptible to small-scale magnetic reconnection. Precursor reconnection activity from this location most likely induced a slipping reconnetion towards the northern leg of the hot channel which led to the destabilization of the flux rope. The application of magnetic virial theorem suggests that there was an overall growth of magnetic free energy in the active region during the prolonged pre-flare phase which decayed rapidly after the hot channel eruption and its successful transformation into a halo coronal mass ejection (CME).

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.

In this article, we present a multi-wavelength and multi-instrument investigation of a halo coronal mass ejection (CME) from active region NOAA 12371 on 21 June 2015 that led to a major geomagnetic storm of minimum $\mathrm{Dst} = -204$ nT. The observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory in the hot EUV channel of 94 A confirm the CME to be associated with a coronal sigmoid that displayed an intense emission ( $T \sim6$ MK) from its core before the onset of the eruption. Multi-wavelength observations of the source active region suggest tether-cutting reconnection to be the primary triggering mechanism of the flux rope eruption. Interestingly, the flux rope eruption exhibited a two-phase evolution during which the “standard” large-scale flare reconnection process originated two composite M-class flares. The eruption of the flux rope is followed by the coronagraphic observation of a fast, halo CME with linear projected speed of 1366 km s−1. The dynamic radio spectrum in the decameter-hectometer frequency range reveals multiple continuum-like enhancements in type II radio emission which imply the interaction of the CME with other preceding slow speed CMEs in the corona within $\approx10$ – $90~\mbox{R} _{\odot}$ . The scenario of CME–CME interaction in the corona and interplanetary medium is further confirmed by the height–time plots of the CMEs occurring during 19 – 21 June. In situ measurements of solar wind magnetic field and plasma parameters at 1 AU exhibit two distinct magnetic clouds, separated by a magnetic hole. Synthesis of near-Sun observations, interplanetary radio emissions, and in situ measurements at 1 AU reveal complex processes of CME–CME interactions right from the source active region to the corona and interplanetary medium that have played a crucial role towards the large enhancement of the geoeffectiveness of the halo CME on 21 June 2015.

Context. For a better understanding of the dynamics of the solar corona, it is important to analyse the evolution of the helicity of the magnetic field. Since the helicity cannot be directly determined by observations, we have recently proposed a method to calculate the relative magnetic helicity in a finite volume for a given magnetic field, which however required the flux to be balanced separately on all the sides of the considered volume. Aims. We developed a scheme to obtain the vector potential in a volume without the above restriction at the boundary. We studied the dissipation and escape of relative magnetic helicity from an active region. Methods. In order to allow finite magnetic fluxes through the boundaries, a Coulomb gauge was constructed that allows for global magnetic flux balance. The property of sinusoidal function was used to obtain the vector potentials at the 12 edges of the considered rectangular volume extending above an active region. We tested and verified our method in a theoretical fore-free magnetic field model. Results. We applied the new method to the former calculation data and found a difference of less than 1.2%. We also applied our method to the magnetic field above active region NOAA 11429 obtained by a new photospheric-data-driven magnetohydrodynamics (MHD) model code GOEMHD3. We analysed the magnetic helicity evolution in the solar corona using our new method. We find that the normalized magnetic helicity (H∕Φ2) is equal to −0.038 when fast magnetic reconnection is triggered. This value is comparable to the previous value (−0.029) in the MHD simulations when magnetic reconnection happened and the observed normalized magnetic helicity (−0.036) from the eruption of newly emerging active regions. We find that only 8% of the accumulated magnetic helicity is dissipated after it is injected through the bottom boundary. This is in accordance with the Woltjer conjecture. Only 2% of the magnetic helicity injected from the bottom boundary escapes through the corona. This is consistent with the observation of magnetic clouds, which could take magnetic helicity into the interplanetary space. In the case considered here, several halo coronal mass ejections (CMEs) and two X-class solar flares originate from this active region.

We have found that solar flares in NOAA active region (AR) 10696 were often associated with large-scale trans-equatorial activities. These trans-equatorial activities appeared to be very common and manifest themselves through i) the formation and eruption of trans-equatorial loops (TELs), ii) the formation and eruption of trans-equatorial filaments (TEFs), and iii) the trans-equatorial brightening (TEB) in the chromosphere. It is determined that the TEF was formed following episodic plasma ejecta from flares occurring in the AR. The TEF eruption was associated with a trans-equatorial flare. All flares in the AR that were accompanied by trans-equatorial activities were associated with halo coronal mass ejections (CMEs). It was noticed that one or several major flares in the AR were followed by an increase of brightness and nonpotentiality of a TEL. These coupled events had a lifetime of more than 12 hours. In addition their associated halo CMEs always had a positive acceleration, indicating prolonged magnetic reconnections in the outer corona at high altitudes.

A solar flare was observed on 1997 April 7 with the Soft X-ray Telescope (SXT) on Yohkoh. The flare was associated with a "halo" coronal mass ejection (CME). The flaring region showed areas of reduced soft X-ray (SXR) brightness—"dimmings"—that developed prior to the CME observed in white light and persisted for several hours following the CME. The most prominent dimming regions were located near the ends of a preflare SXR S-shaped (sigmoid) feature that disappeared during the event, leaving behind a postflare SXR arcade and cusp structure. Based upon these and similar soft X-ray observations, it has been postulated that SXR dimming regions are the coronal signatures (i.e., remnants) of magnetic flux ropes ejected during CMEs. This Letter reports new observations of coronal dimming at extreme-ultraviolet (EUV) wavelengths obtained with the Extreme-ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO). A series of EIT observations in the 195 Å Fe XII wavelength band were obtained simultaneously with SXT during the 1997 April 7 flare/CME. The EIT observations show that regions of reduced EUV intensity developed at the same locations and at the same time as SXR dimming features. The decrease in EUV intensity (averaged over each dimming region) occurred simultaneously with an increase in EUV emission from flaring loops in the active region. We interpret these joint observations within the framework of flux-rope eruption as the cause of EUV and SXR coronal dimmings, and as the source of at least part of the CME.

There appear indications of more global activity on the Sun which is larger, much beyond the scale of solar active regions (ARs). These indications include formation, flaring and eruption of the trans-equatorial loops seen in EUV and X-rays, formation and eruption of trans-equatorial filaments, global magnetic connectivity in EUV dimming associated with halo-coronal mass ejections, wide spread of radio burst sources in meter wavelength in the solar corona, and quasi-simultaneous magnetic flux emergence in both hemispheres seen during some major solar events. With examples of a few major events in the last solar cycle we discuss the possibility that there is large or global-scale activity on the Sun. Its spatial scale is many times larger than that of AR and temporal scale is over 10 hours. The exemplified trans-equatorial loops are anchored in ARs and their activity is temporally associated with flares in ARs too. In some sense the flares in ARs appear either as a part of or a precursor of the more global activity. It is likely that the combination of the flares in ARs and the associated global activity is responsible to the major solar-terrestrial events. More efforts in understanding the global activity are undertaken.

SPE is one of the most severe hazards in the space environment. Such events tend to occur during periods of intense solar activity and can lead to high radiation doses in short time intervals. The proton enhancements produced by these solar events may last several days and are very hard to predict in advance, and they also can cause harm both satellites and humans in space. The most significant proton sources in the interplanetary medium are both solar flares and interplanetary shocks driven by coronal mass ejections (CMEs). In this study, I try to find the characteristic of flare and CME that can cause the proton events in the interplanetary medium. For my preliminary study, I will search flare characteristics such as class and position as SPE cause. I also researched with CME characteristics such as Angular Width (AW) and linear speed. During solar cycle 24, the solar activity remains very low with several large flares and halo CME. This low activity also occurs on solar proton events in interplanetary medium. From January 2009 to December 2019, there were 46 SPEs with flux range from 11—6530 pfu (10 meV). The solar flares during these events varies from C to X- class flare. From 45 X-class flares that occurs during 2009—2019, only 11 flares cause the SPE. Most of the active region locations are at the solar western hemisphere (35/46). There are 40 from 323 halo CME (AW = 360°), 37 from 203 with linear speed >1000 km/s, and 34 from 109 Halo CME with linear speed >1000 km/s cause SPE. Although the probability of SPE from all flares and CMEs during this range of time is small, but they have three common characteristics, i.e., most of the SPE has active region position at the solar western hemisphere, the CME have AW = 360°, and have a high linear speed.KeywordsSolar Proton EventsFlareCoronal Mass Ejections