Multi-wavelength observations of an X-class flare without a coronal mass ejection.

Coronal mass ejections (CMEs) are solar eruptions that involve large-scale changes to the magnetic topology of an active region. There exists a range of models for CME onset which are based on twisted or sheared magnetic field above a polarity inversion line (PIL). We present observational evidence that topological changes at PILs, in the photosphere, form a key part of CME onset, as implied by many models. In particular, we study the onset of 30 CMEs and investigate topological changes in the photosphere by calculating the magnetic winding flux, using the artop code. By matching the times and locations of winding signatures with CME observations produced by the almanac code, we confirm that these signatures are indeed associated with CMEs. Therefore, as well as presenting evidence that changes in magnetic topology at the photosphere are a common signature of CME onset, our approach also allows for the finding of the source location of a CME within an active region.

Many aspects of the Sun‐Mars interaction have been investigated during solar transient events with measurements from multiple spacecrafts and also simulation efforts. Limited discussion has been paid to magnetic topology response to disturbed upstream conditions. The implications of topology changes include, but are not limited to, the pattern of energetic particle precipitation into the Martian atmosphere and the impact on cold ion escape during solar transient events as low‐energy ion escape is dependent on magnetic topology. In this study, we investigate the magnetic topology response to the 2017 September interplanetary coronal mass ejection (ICME) event with measurements collected by the Mars Atmospheric and Volatile EvolutioN spacecraft. It is found that the interface between draped interplanetary magnetic field and closed field lines was moved from 800–1400 km in altitude during quiet conditions to 200–400 km after ICME arrived at Mars and then relaxed back to high altitudes again after the event. To gain insight into magnetic topology response on a global scale, we first validate magnetic topology from a time‐dependent simulation with a single‐fluid multispecies magnetohydrodynamic (MHD) model by comparing magnetic topology determined from Mars Atmospheric and Volatile EvolutioN data, which shows a good agreement. Then we present MHD predictions of global magnetic topology changes during this ICME event. In addition to a deeper interplanetary magnetic field penetration, MHD results suggest more open field lines in response to the ICME event.

The idea of 'frozen-in' magnetic field lines for ideal plasmas is useful to explain diverse astrophysical phenomena, for example the shedding of excess angular momentum from protostars by twisting of field lines frozen into the interstellar medium. Frozen-in field lines, however, preclude the rapid changes in magnetic topology observed at high conductivities, as in solar flares. Microphysical plasma processes are a proposed explanation of the observed high rates, but it is an open question whether such processes can rapidly reconnect astrophysical flux structures much greater in extent than several thousand ion gyroradii. An alternative explanation is that turbulent Richardson advection brings field lines implosively together from distances far apart to separations of the order of gyroradii. Here we report an analysis of a simulation of magnetohydrodynamic turbulence at high conductivity that exhibits Richardson dispersion. This effect of advection in rough velocity fields, which appear non-differentiable in space, leads to line motions that are completely indeterministic or 'spontaneously stochastic', as predicted in analytical studies. The turbulent breakdown of standard flux freezing at scales greater than the ion gyroradius can explain fast reconnection of very large-scale flux structures, both observed (solar flares and coronal mass ejections) and predicted (the inner heliosheath, accretion disks, γ-ray bursts and so on). For laminar plasma flows with smooth velocity fields or for low turbulence intensity, stochastic flux freezing reduces to the usual frozen-in condition.

Interplanetary coronal mass ejections (ICMEs) are the heliospheric counterparts of solar coronal mass ejections, and their comprehensive cataloging near Earth has enabled significant advances across space science disciplines. As a part of the Project Space Life by Eco Astronomy Inc, this review presents a synthesis of the Near-Earth ICME since 1996” dataset compiled by I. G. Richardson and H. V. Cane, highlighting its historical development, methodology, key findings, and broad applications. The dataset encompasses approximately 600 ICMEs observed at 1 AU from 1996 through early 2024, spanning solar cycles 23, 24, and the rise of 25. We discuss how ICMEs are identified using in-situ plasma, magnetic field, composition, and energetic particle signatures, and how this approach has evolved with improved data (e.g. ACE spacecraft measurements). The ICME catalogs reveals clear solar-cycle trends, ICME occurrence rises by an order of magnitude from solar minimum to maximum with the yearly counts peaking in 2000 (51 events) and dipping to only a few events at recent minima. It also captures intriguing temporal patterns such as a quasi-periodicity of ~150 days in ICME occurrence (Cane & Richardson, January 1, 2003). We synthesize the typical ICME properties (duration, speed, magnetic field strength) and how they vary between cycles: e.g. cycle 23 produced more frequent and faster ICMEs than the weaker cycle 24. The dataset’s extensive annotations (footnotes) link each ICME to associated phenomena like geomagnetic sudden commencements, storm indices, and cosmic ray depressions, allowing analysis of ICME impacts. We review how ~90% of major geomagnetic storms (Dst ≤ –100 nT) in 1996–2005 were caused by ICMEs or their driven shocks (Richardson & Cane, 2007), underlining their geo effectiveness. We summarize statistical correlations between ICME parameters (speed, magnetic field, size) and geomagnetic storm intensity and discuss notable events. Beyond geomagnetism, ICMEs are shown to modulate galactic cosmic rays, causing short-term intensity drops (Forbush decreases) in ~80% of cases (I & H, 2011) and contributing to long-term cosmic-ray modulation over the solar cycle. The rich Richardson-Cane ICME database has fostered multidisciplinary benefits: improving space weather forecasts (by providing empirical event data for CME arrival and storm predictions), informing heliospheric physics (e.g. ICME propagation and solar-cycle variability), elucidating cosmic ray transport (through ICME-caused particle decreases), and aiding studies of impacts on technological systems (satellites, power grids, GPS) and Earth’s atmosphere. We conclude by emphasizing the value of this continually updated ICME catalogs for future research and cross-disciplinary applications, and we include a comprehensive appendix of ICME analysis figures derived from the dataset.

The intensity of the southward component of the magnetic field (Bs) carried by Interplanetary Coronal Mass Ejections (ICMEs) is one of the most critical parameters in causing extreme space weather events, such as intense geomagnetic storms. In this work, we investigate three typical ICME events with extremely intense Bs in detail and present a statistical analysis of the origins of intense Bs in different types of ICMEs based on the ICME catalogue from 1995 to 2020. According to the in-situ characteristics, the ICME events with extremely high Bs are classified into three types: isolated ICMEs, multiple ICMEs, and shock-ICME interaction events with shocks inside ICMEs or shocks passing through ICMEs. By analyzing all ICME events with Bs ≥ 10nT and Bs ≥ 20nT, we find that 39.6% of Bs,mean ≥ 10nT events and 50% of Bs,mean ≥ 20nT events are associated with shock-ICME events. Approximately 35.7% of shock-ICME events have Bs,mean ≥ 10nT, which is much higher than the other two types (isoloted ICMEs: 7.2% and multiple ICMEs: 12.1%). Those results confirm that the ICMEs interaction events are more likely to carry extreme intense Bs and cause intense geomagntic storms. Only based on the in-situ observations at Earth, some interaction ICME events, such as shock-ICME interaction events with shocks passing through the preceding ICME or ICME cannibalism, could be classified as isolated ICME events. This may lead to an overestimate of the probability of ICME carrying extremely intense Bs. To further investigate such events, direct and multi-point observations of the CME propagation in the inner heliosphere from the Solar Ring Mission could be crucial in the future.

We discuss the post-eruptive evolution of a "coronal dimming" based on observations of the EUV corona from the Solar and Heliospheric Observatory and the Transition Region and Coronal Explorer. This discussion highlights the roles played by magnetoconvection-driven magnetic reconnection and the global magnetic environment of the plasma in the "filling" and apparent motion of the region following the eruption of a coronal mass ejection (CME). A crucial element in our understanding of the dimming region evolution is developed by monitoring the disappearance and reappearance of bright TRACE "moss" around the active region giving rise to the CME. We interpret the change in the TRACE moss as a proxy of the changing coronal magnetic field topology behind the CME front. We infer that the change in global magnetic topology also results in a shift of energy balance in the process responsible for the production of the moss emission while the coronal magnetic topology evolves from closed, to open and back to closed again because, following the eruption, the moss reforms around the active region in almost exactly its pre-event configuration. As a result of the moss evolution, combining our discussion with recent spectroscopic results of an equatorial coronal hole, we suggest that the interchangeable use of the term "transient coronal hole" to describe a coronal dimming is more than just a simple coincidence.

Abstract. The apparent contradiction between small-scale source regions of, and large-scale coronal response to, coronal mass ejections (CMEs) has been a long-standing puzzle. For some, CMEs are considered to be inherently large-scale events – eruptions in which a number of flux systems participate in an unspecified manner, while others consider magnetic reconnection in special global topologies to be responsible for the large-scale response of the lower corona to CME events. Some of these ideas may indeed be correct in specific cases. However, what is the key element which makes CMEs large-scale? Observations show that the extent of the coronal disturbance matches the angular width of the CME – an important clue, which does not feature strongly in any of the above suggestions. We review observational evidence for the large-scale nature of CME source regions and find them lacking. Then we compare different ideas regarding how CMEs evolve to become large-scale. The large-scale magnetic topology plays an important role in this process. There is amounting evidence, however, that the key process is magnetic reconnection between the CME and other magnetic structures. We outline a CME evolution model, which is able to account for all the key observational signatures of large-scale CMEs and presents a clear picture how large portions of the Sun become constituents of the CME. In this model reconnection is driven by the expansion of the CME core resulting from an over-pressure relative to the pressure in the CME's surroundings. This implies that the extent of the lower coronal signatures match the final angular width of the CME.

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.

In situ observations of interplanetary (IP) coronal mass ejections (ICMEs) and IP shocks are important to study as they are the main components of solar activity. Hundreds of IP shocks have been detected by various space missions at different times and heliocentric distances. Some of these are followed by clearly identified drivers, while some others are not. In this study, we carry out a statistical analysis of the distributions of plasma and magnetic parameters of the IP shocks recorded at various distances to the Sun. We classify the shocks according to the heliocentric distance, namely from 0.29 to 0.99 AU (Helios-1/2); near 1 AU (Wind, ACE, and STEREO-A/B); and from 1.35 to 5.4 AU (Ulysses). We also differentiate the IP shocks into two populations, those with a detected ICME and those without one. As expected, we find that there are no significant differences in the results from spacecraft positioned at 1 AU. Moreover, the distributions of shock parameters, as well as the shock normal, have no significant variations with the heliocentric distance. Additionally, we investigate how the number of shocks associated with stream-interaction regions (SIRs) increases with distance in the proportion to ICME/shocks. From 1 to 5 AU, SIRs/ shock occurrence increases slightly from 21% to 34%; in contrast, ICME/shock occurrence decreases from 47% to 17%. We also find indication of an asymmetry induced by the Parker spiral for SIRs and none for ICMEs.

Sunspot is known as the area with the highest solar magnetic activity and has the coolest region compared to its surrounding. It is also influenced by sunspot complexity and magnetic field strength. The huge explosion of solar energetic particles in the interplanetary space due to Coronal Mass Ejections (CMEs) and solar flares is believed due to instability of magnetic field and complexity magnetic field in the sunspot. Due to these events, the intense solar radio emission also known as solar radio bursts were released to the Earth. Delta (δ) sunspot is one of the largest magnetic classification of sunspot and seen mostly released solar flares and CMEs, however, Beta Gamma (βγ) sunspot has the highest formation from 2012 to 2016 compared to other type of bursts and has tendency to produce solar flares and CMEs. The data were collected using Space Weather Website (SWPC) and NOAA, e-CALLISTO network and LPDA. The data were collected within 5 years (2012-2016) and reveals βγ sunspot has (349 counts) (62.77%), followed by βγσ sunspot (160 counts) (28.78%), δ sunspot (39 counts) (7.01%) and βγ sunspot (8 counts) (1.44%), thus, highlights the highest type of magnetic classification occurred on Active Region (AR) was βγ sunspot. Highest formation of βγ sunspot illustrated the complexity of the βγ sunspot due instability of magnetic field inside AR and has tendency to produce flares and CMEs compared to other types of magnetic classifications. Furthermore, βγ sunspot demonstrated a tendency to generate Type II burst, Type III burst, Type IV burst and combination of bursts which we classified as selected events. This finding proved that Type IV burst has the highest formation of burst followed by Type III burst, Type II burst and selected events. Type IV burst has counted for 161 counts (56.29%), Type III burst (100 counts) (34.96%), Type II burst (14 counts) (4.9%) and selected events (11 days) (3.85%). The type of bursts was determined by the range frequency of burst and the duration of burst. The different types of bursts have different ranges of frequency and duration of bursts. Type IV burst displayed the highest formation due its associated phenomena mostly was sunspot where the location of events occurred, followed by Type III burst (solar flares), Type II burst (CMEs) and selected events. These findings were important in solar activity study as prediction and forecast for Solar Cycle 25. These significant findings manage the process of shutting down the system from breakdown due to high energetic particles being released from solar flares and CMES. This prediction can shut down the system in satellites and prevent the power grid and telecommunication system from breakdown.

The prevailing framework of understanding coronal mass ejections (CMEs) and, indeed, solar eruptions in general is the hypothesis that the quasi-static changes in the photospheric magnetic field increases the magnetic energy in the corona and causes sudden release of the stored energy. However, this hypothesis, which may be called the `storage-release' paradigm, has yet to produce a quantitative model of CMEs and their heliospheric consequences. Recently, a new theory has been proposed to explain the physics of CMEs. This theory posits that the initial structure is a magnetic flux rope that is ultimately connected to the solar dynamo in the convection zone and that magnetic energy propagating from the source along the submerged magnetic structure enters the corona and drives the eruption. Specifically, the theory describes CMEs as the dynamical response of coronal flux ropes to the `injected' poloidal flux and predicts that CMEs evolve into interplanetary magnetic clouds (MCs). In a recent series of studies, the physics-based theory was shown to correctly describe the observed dynamics of a class of CMEs and the properties of MCs, providing the first unified description of the CME-MC dynamics. The apparent success of the theory suggests a new paradigm in which CMEs are viewed as a relaxation process in response to the increased magnetic energy propagating from the dynamo. The motion of a flux rope and its magnetic energy is everywhere given by \(\tilde \upsilon \lesssim 1\), where \(\tilde \upsilon \equiv \upsilon /V_M {\text{ and }}V_M \) is the local characteristic speed. It is predicted that the injected poloidal flux can cause a subtle but distinct signature in the tangential field at the base of the corona. The tangential field, which is difficult to observe, and the poloidal magnetic energy have been neglected in previous theories. This paper reviews the current CME research, compares the physics of the two competing paradigms, and suggests new observable magnetic field signatures.

The most powerful explosions on the Sun – in the form of bright flares, intense storms of solar energetic particles (SEPs), and fast coronal mass ejections (CMEs) – drive the most severe space‐weather storms. Proxy records of flare energies based on SEPs in principle may offer the longest time base to study infrequent large events. We conclude that one suggested proxy, nitrate concentrations in polar ice cores, does not map reliably to SEP events. Concentrations of select radionuclides measured in natural archives may prove useful in extending the time interval of direct observations up to ten millennia, but as their calibration to solar flare fluences depends on multiple poorly known properties and processes, these proxies cannot presently be used to help determine the flare energy frequency distribution. Being thus limited to the use of direct flare observations, we evaluate the probabilities of large‐energy solar events by combining solar flare observations with an ensemble of stellar flare observations. We conclude that solar flare energies form a relatively smooth distribution from small events to large flares, while flares on magnetically active, young Sun‐like stars have energies and frequencies markedly in excess of strong solar flares, even after an empirical scaling with the mean coronal activity level of these stars. In order to empirically quantify the frequency of uncommonly large solar flares extensive surveys of stars of near‐solar age need to be obtained, such as is feasible with the Kepler satellite. Because the likelihood of flares larger than approximately X30 remains empirically unconstrained, we present indirect arguments, based on records of sunspots and on statistical arguments, that solar flares in the past four centuries have likely not substantially exceeded the level of the largest flares observed in the space era, and that there is at most about a 10% chance of a flare larger than about X30 in the next 30 years.

Coronal mass ejections (CMEs) are large-scale eruptions of magnetized plasma from the Sun's lower atmosphere, significantly influencing space weather and planetary environments. To improve predictions of CME arrival and their impacts on Earth and its surroundings, a deeper understanding of their origins, initiation, and complex early evolution is crucial. While coronagraphic observations have been essential for studying the dynamics of CMEs, they cannot capture the initial, critical phase of CME development. Consequently, investigating indirect phenomena in the lower solar atmosphere has become essential. One of the most prominent indirect indicators associated with CMEs is coronal dimming. These are localized, sudden decreases in coronal emission observed at extreme ultraviolet and soft X-ray wavelengths, which evolve rapidly during the lift-off and early expansion phases of CMEs. Coronal dimmings have been interpreted both as “footprints” of the erupting magnetic structure and as indicators of coronal mass loss in the lower corona.I will review recent advancements in using coronal dimmings to diagnose CMEs. Topics covered will include statistical studies linking dimming characteristics to CME mass and speed, the use of dimmings as early indicators of CME propagation direction, and insights into the magnetic topology and reconfiguration of the early CME stages based on dimming locations and fine structure. Additionally, the potential role of dimmings in the pre-event phase preceding CME onset will be discussed. Finally, I will highlight future research directions and underexplored areas in CME science, emphasizing the untapped potential of coronal dimmings in advancing our understanding of these dynamic solar events.

The period between late October and early November of 2003 included a series of large solar events that resulted in some of the most extreme space weather of the current solar cycle. Space weather has been defined as the conditions on the sun and in the solar wind, magnetosphere, ionosphere, and thermosphere that can influence the performance and reliability of space-borne and ground-based technological systems. Adverse conditions in the space environment can cause disruption of satellite operations, communications, navigation, and electric power distribution grids, leading to a variety of socioeconomic losses (National Science Foundation 2000). The space weather events of October–November 2003 were initiated by three very large sunspot clusters that became visible on the Sun over a period of approximately 7 days beginning on 18 October, 2003. One of these clusters, region 486, became the largest sunspot group of the current solar cycle and the largest seen since 1991. This sudden increase in sunspots induced a series of solar flares and coronal mass ejections (CMEs), (Department of Commerce 2004). Solar flares are explosions on the surface of the Sun that produce a quick directed high-speed blast of charged particles and electromagnetic energy. One of the largest solar flares ever seen on the Sun occurred on 28 October. It was the third largest detected since regular monitoring began approximately 30 years ago and the largest since April 2001 (US Department of Commerce 2004). This activity was accompanied by a CME. CME’s are huge bubbles of plasma ejected from the Sun that speed into space. They disrupt the flow of the solar wind and produce disturbances that can strike the Earth with sometimes-catastrophic results (http://science.nasa.gov/ssl/pad/solar/ cmes.htm). This particular CME was one of the fastest on record in that it left the sun with a speed of 2,500 km/s, five times the average speed (Murtagh 2004). Figure 1 illustrates the observed active regions on 27 October together with the images of the solar flare and CME recorded on 28 October as observed by the SOHO spacecraft (http://sohowww.nascom.nasa.gov/). These events resulted in a severe geomagnetic storm in the Earth’s environment at 06:00 UT on 29 October. The disturbance levels on the Sun remained high for several days with a second powerful CME occurring at approximately 21:00 UT on 29 October. Figure 2 illustrates the planetary 3-h Kp indices for the period of 29 October 2003 to 1 November 2003. The Kp index is derived from 13 global magnetic observatories. It is a measure of the disturbance level of the geomagnetic field by auroral ionospheric currents. Kp values greater than 4 represent disturbed conditions. As the Kp values increase, the severity of the storm increases. Kp values of 9 represent the most extreme disturbed conditions and occur only a few times during the course of each 11-year solar cycle (http://www.sec.noaa.gov/NOAAscales). Note that Kp values of 9 were reached multiple times during 29–30 October in response to the CME activity.

Abstract. The Sun was extremely active during the "April Fool’s Day" epoch of 2001. We chose this period between a solar flare on 28 March 2001 to a final shock arrival at Earth on 21 April 2001. The activity consisted of two presumed helmet-streamer blowouts, seven M-class flares, and nine X-class flares, the last of which was behind the west limb. We have been experimenting since February 1997 with real-time, end-to-end forecasting of interplanetary coronal mass ejection (ICME) shock arrival times. Since August 1998, these forecasts have been distributed in real-time by e-mail to a list of interested scientists and operational USAF and NOAA forecasters. They are made using three different solar wind models. We describe here the solar events observed during the April Fool’s 2001 epoch, along with the predicted and actual shock arrival times, and the ex post facto correction to the real-time coronal shock speed observations. It appears that the initial estimates of coronal shock speeds from Type II radio burst observations and coronal mass ejections were too high by as much as 30%. We conclude that a 3-dimensional coronal density model should be developed for application to observations of solar flares and their Type II radio burst observations.Key words. Interplanetary physics (flare and stream dynamics; interplanetary shocks) – Magnetosheric physics (storms and substorms)