Powerful Coronal Mass Ejections Research Articles

Which Upstream Solar Wind Conditions Matter Most in Predicting Bz Within Coronal Mass Ejections

AbstractAccurately predicting the z‐component of the interplanetary magnetic field, particularly during the passage of an interplanetary coronal mass ejection (ICME), is a crucial objective for space weather predictions. Currently, only a handful of techniques have been proposed and they remain limited in scope and accuracy. Recently, a robust machine learning technique was developed for predicting the minimum value of Bz within ICMEs based on a set of 42 “features,” that is, variables calculated from measured quantities upstream of the ICME and within its sheath region. In this study, we investigate these so‐called explanatory variables in more detail, focusing on those that were (a) statistically significant and (b) most important. We find that number density and magnetic field strength accounted for a large proportion of the variability. These features capture the degree to which the ICME compresses the ambient solar wind ahead. Intuitively, this makes sense: Energy made available to coronal mass ejections (CMEs) as they erupt is partitioned into magnetic and kinetic energy. Thus, more powerful CMEs are launched with larger flux‐rope fields (larger Bz), at greater speeds, resulting in more sheath compression (increased number density and total field strength).

Solar Longitude Distribution of High-energy Proton Flares: Fluences and Spectra

Abstract The distribution of the longitudes of solar flares associated with the high-energy proton events called ground level events (GLEs) can be approximated by a Gaussian with a peak at ∼W60, with a full range from ∼E90 to ∼W150. The longitudes of flares associated with the top third (24 of 72) of GLEs in terms of their >430 MeV fluences (F 430) are primarily distributed over E20–W100 with a skew toward disk center. This 120° span in longitude is comparable to the latitudinal spans of powerful coronal mass ejections (CMEs) from limb flares. Only 5 of 24 strong GLEs are located within the W40–80 zone of good magnetic connection to Earth. GLEs with hard spectra, i.e., a spectral index SI30/200(= log(F 30/F 200)) < 1.5, also tend to avoid W40–80 source regions. Three-fourths of such events (16 of 21) arise in flares outside this range. The above tendencies favor a CME-driven shock source over a flare-resident acceleration process for high-energy solar protons. GLE spectra show a trend, with broad scatter, from hard spectra for events originating in eruptive flares beyond the west limb to soft spectra for GLEs with sources near central meridian. This behavior can be explained in terms of: (1) dominant near-Sun quasi-perpendicular shock acceleration of protons for far western (>W100) GLEs; (2) quasi-parallel shock acceleration for well-connected (W40–80) GLEs, and (3) proton acceleration/trapping at CME-driven bow shocks from central meridian (E20–W20) that strike the Earth.

Studying Powerful Coronal Mass Ejections That Occurred in September 2017, According to Data from the URAGAN Muon Hodoscope

At the beginning of September 2017, the Sun was characterized by anomalously high solar activity (SA), which was unusual for the region of the minimum of the 11-year cycle. A great many powerful flares of the M- and X-classes were observed; these were accompanied by powerful coronal mass ejections (CMEs). These events caused strong magnetic storms on the Earth (the Kp index was as high as 8; the Dst index was <−140 nT). In this work, the effect these ejections had on the flux of cosmic rays (CRs) is considered using data from the URAGAN muon hodoscope at the Moscow Engineering Physics Institute. The study is based on an analysis of variations in the cosmic ray muon flux. Results are presented from processing flux intensity via flicker-noise spectroscopy in order to identify geoeffective disturbances of the Earth’s magnetosphere. A predictor that precedes by more than one day the emergence in near-Earth space of disturbances related to CME propagation is obtained.

Geometry, Kinematics, and Heliospheric Impact of a Large CME-driven Shock in 2017 September

Abstract A powerful coronal mass ejection (CME) occurred on 2017 September 10 near the end of the declining phase of the historically weak solar cycle 24. We obtain new insights concerning the geometry and kinematics of CME-driven shocks in relation to their heliospheric impacts from the optimal, multispacecraft observations of the eruption. The shock, which together with the CME driver can be tracked from the early stage to the outer corona, shows a large oblate structure produced by the vast expansion of the ejecta. The expansion speeds of the shock along the radial and lateral directions are much larger than the translational speed of the shock center, all of which increase during the flare rise phase, peak slightly after the flare maximum and then decrease. The near simultaneous arrival of the CME-driven shock at the Earth and Mars, which are separated by 156.°6 in longitude, is consistent with the dominance of expansion over translation observed near the Sun. The shock decayed and failed to reach STEREO A around the backward direction. Comparison between ENLIL MHD simulations and the multipoint in situ measurements indicates that the shock expansion near the Sun is crucial for determining the arrival or nonarrival and space weather impact at certain heliospheric locations. The large shock geometry and kinematics have to be taken into account and properly treated for accurate predictions of the arrival time and space weather impact of CMEs.

Effects of Solar Activity on the Local Interstellar Magnetic Field Observed by Voyager 1 and IBEX

Abstract Interstellar Boundary Explorer (IBEX) observations have shown enhanced energetic neutral atom emission from a narrow, circular ribbon likely centered on the direction of the magnetic field in the local interstellar medium (LISM). IBEX observations are compared to Voyager 1's direct observations of the magnetic field in the LISM, which reveals structured changes that are shown here to be driven by pressure fluctuations transmitted across the heliopause boundary separating the LISM from the shocked solar wind beyond the termination shock. The changes in the local interstellar magnetic field observed by Voyager 1 occurred in 2015 and 2016, when the most powerful coronal mass ejections released from the Sun over the last 11-year solar cycle arrived in the outer heliosphere. These events propagated over more than two years through the solar system, ultimately pounding the heliopause and causing transient deviations of the magnetic fields detected by Voyager 1 in the LISM. Thus, we identify the response in pressure variations at Voyager 1 in the LISM with the activity of major solar events several years earlier, during the most active period of the last solar maximum.

The early Earth under a superflare and super-CME attack: prospects for life

AbstractKepler observations suggest that G-type stars produce powerful flares suggesting that the early Earth may also have been exposed to frequent and energetic solar explosive events generated by the young Sun. We show that powerful coronal mass ejection (CME) events associated with superflares impacting the Earth magnetosphere with a frequency of 1 event/day. What was the impact of superflares, CMEs and associated solar energetic particle (SEPs) events on the atmospheric erosion of the young Earth and habitability? In this paper we discuss our three-dimensional (3D) magnetohydrodynamic (MHD) simulations that show that frequent and energetic CMEs from the early Sun continuously destroyed the sub-solar parts of Earth's magnetosphere at heights &lt; 1.25 RE. This suggests that CME shock accelerated energetic protons are capable of penetrating into the polar cap region and breaking atmospheric molecular nitrogen, the major ingredient of the early Earth atmosphere, into atomic nitrogen. Photo-collisional dissociation of molecular nitrogen and carbon dioxide creates reactive chemistry that efficiently produces nitrous oxide and hydrogen cyanide, the essential molecule in prebiotic life chemistry. This raises an possibility that frequent super-CMEs could serve as a potential catalyst for the origin of life on early Earth.

Powerful non-geoeffective interplanetary disturbance of July 2012 observed by muon hodoscope URAGAN

The most powerful coronal mass ejection of the 24th solar cycle took place on the opposite side of the Sun on July 23, 2012 and had no geomagnetic consequences. Nevertheless, as a result of passing of the ejection through the heliosphere, variations of galactic cosmic rays flux were observed on the Earth. These variations were registered by the muon hodoscope URAGAN (MEPhI, Moscow). Muon flux angular distributions on the Earth’s surface are reported and analyzed.

Stellar wind erosion of protoplanetary discs

An analytic model is developed for the erosion of protoplanetary gas discs by high velocity magnetized stellar winds. The winds are centrifugally driven from the surface of rapidly rotating, strongly magnetized young stars. The presence of the magnetic field in the wind leads to Reynolds numbers sufficiently large to cause a strongly turbulent wind/disk boundary layer which entrains and carries away the disc gas. The model uses the conservation of mass and momentum in the turbulent boundary layer. The time-scale for significant erosion depends on the disc accretion speed and accretion rate and on the wind mass loss rate and the wind velocity. The time-scale is estimated to be 2E6 yr. A significant contribution to the disc erosion can come from frequent powerful coronal mass ejections (CMEs) where the average mass loss rate in CMEs and velocities have values comparable to those for the steady wind.

Dynamics of fluxes of protons with energies 30–80 keV during geomagnetic storms on January 21–22, 2005, and December 14–15, 2006, according to data from low-orbit satellites

We present the results of a comparative analysis of the dynamics of three populations of fluxes of protons with energy 30–80 keV as measured by NOAA solar-synchronous satellites (POES 15, 16, 17) at low latitudes (L < 2) and at latitudes lower and higher than the boundary of isotropic precipitation during the geomagnetic storms on January 21–22, 2005 and December 14–15, 2006. Based on a complex analysis of experimental data on particle fluxes at low orbits and on measurements of solar wind parameters performed by the ACE spacecraft, we have studied the dynamical peculiarities of the fluxes of particles and of their longitudinal distributions depending on the conditions in the interplanetary medium. It is shown that an increase of trapped particle fluxes and the development of the main phase of the geomagnetic storm on January 21–22, 2005 are associated with the magnetosphere’s response to a prolonged action of an extremely powerful coronal mass ejection at a northern orientation of the IMF. On December 14, 2006 an insufficient amplitude and duration of the pressure impulse did not result in development of a disturbance similar to January 21–22, 2005. The development of the main phase of this storm is related to a southward turn of the IMF, which has occurred only seven hours after the SSC.

"Almost destroyed world"? Journalists planetwide report danger from the Sun

Scientists warn we should waste no time in learning from a powerful coronal mass ejection.

A major solar eruptive event in July 2012: Defining extreme space weather scenarios

AbstractA key goal for space weather studies is to define severe and extreme conditions that might plausibly afflict human technology. On 23 July 2012, solar active region 1520 (~141°W heliographic longitude) gave rise to a powerful coronal mass ejection (CME) with an initial speed that was determined to be 2500 ± 500 km/s. The eruption was directed away from Earth toward 125°W longitude. STEREO‐A sensors detected the CME arrival only about 19 h later and made in situ measurements of the solar wind and interplanetary magnetic field. In this paper, we address the question of what would have happened if this powerful interplanetary event had been Earthward directed. Using a well‐proven geomagnetic storm forecast model, we find that the 23–24 July event would certainly have produced a geomagnetic storm that was comparable to the largest events of the twentieth century (Dst ~ −500 nT). Using plausible assumptions about seasonal and time‐of‐day orientation of the Earth's magnetic dipole, the most extreme modeled value of storm‐time disturbance would have been Dst = −1182 nT. This is considerably larger than estimates for the famous Carrington storm of 1859. This finding has far reaching implications because it demonstrates that extreme space weather conditions such as those during March of 1989 or September of 1859 can happen even during a modest solar activity cycle such as the one presently underway. We argue that this extreme event should immediately be employed by the space weather community to model severe space weather effects on technological systems such as the electric power grid.

RATAN-600 microwave observations of powerful active regions from October 23 to November 5, 2003

Application of the mode of azimuthal observations on RATAN-600 has made it possible to realize multiple daily observations [1]. The results of multiwavelength observations of the Sun in this mode point to the existence of sharp spectral irregularities in the polarized radiation of flare-productive active regions (FPARs) producing especially powerful flares [2]. These phenomena occur in a broad range of radio-emission fluxes (0.05–200 s.f.u.), in a rather narrow wavelength band (2–5 cm), and they are recorded during the time interval from several hours to several days before a powerful flare, as well as during the flare. Frequently, such events indicate an eruption of powerful coronal mass ejections and high-energy particle (proton) fluxes, which, when reaching the Earth’s magnetosphere, trigger its disturbances. Here, we analyze events in the microwave band connected with the strongest flares which took place on October 28 and November 4, 2003.

Common features in the development of powerful long-duration solar X-ray flares

We have begun an investigation of the possible origins of considerable of powerful solar flares. This effect is manifest, first and foremost, in the existence of high-temperature plasma in flare loops over many hours. Analysis of the soft X-ray emission in two energy bands detected by the GOES satellites for about 20 powerful solar flares reveals long time intervals during the decay phase when the source temperature decreases, in general, exponentially. The characteristic time ti for a decrease in the temperature by a factor of ten is 3–10 hours for most powerful events. In addition, another interval of very slow decrease with a characteristic time ti of tens of hours can be identified in some cases. We found a gradual change in the dependence of the temperature on the square root of the emission measure for the source as a whole, which characterizes the transition from purely coronal processes to powerful flares with a prolonged inflow of plasma from the chromosphere. Modeling the energy balance in a loop can yield the requirements for the source of plasma heating in a long-lived arch system. A necessary condition for the development of prolonged flares seems to be a powerful coronal mass ejection, which initiates the formation of a source of plasma heating at coronal heights. Our analysis shows that a considerable fraction of the energy is often released in the region of the cusp, and that systems of giant coronal arches rising to heights of about 100 000 km above the limb are formed in most prolonged events (called dynamical flares in the terminology of Svestka).

On Heating the Sun’s Corona by Magnetic Explosions: Feasibility in Active Regions and Prospects for Quiet Regions and Coronal Holes

We build a case for the persistent strong coronal heating in active regions and the pervasive quasi-steady heating of the corona in quiet regions and coronal holes being driven in basically the same way as the intense transient heating in solar flares: by explosions of sheared magnetic fields in the cores of initially closed bipoles. We begin by summarizing the observational case for exploding sheared core fields being the drivers of a wide variety of flare events, with and without coronal mass ejections. We conclude that the arrangement of an event's flare heating, whether there is a coronal mass ejection, and the time and place of the ejection relative to the flare heating are all largely determined by four elements of the form and action of the magnetic field: (1) the arrangement of the impacted, interacting bipoles participating in the event, (2) which of these bipoles are active (have sheared core fields that explode) and which are passive (are heated by injection from impacted active bipoles), (3) which core field explodes first, and (4) which core-field explosions are confined within the closed field of their bipoles and which ejectively open their bipoles. We then apply this magnetic-configuration framework for flare heating to the strong coronal heating observed by the Yohkoh Soft X-ray Telescope in an active region with strongly sheared core fields observed by the MSFC vector magnetograph. All of the strong coronal heating is in continually microflaring sheared core fields or in extended loops rooted against the active core fields. Thus, the strong heating occurs in field configurations consistent with the heating being driven by frequent core-field explosions that are smaller but similar to those in confined flares and flaring arches. From analysis of the thermal and magnetic energetics of two selected core-field microflares and a bright extended loop, we find that (1) it is energetically feasible for the sheared core fields to drive all of the coronal heating in the active region via a staccato of magnetic microexplosions, (2) the microflares at the feet of the extended loop behave as the flares at the feet of flaring arches in that more coronal heating is driven within the active bipole than in the extended loop, (3) the filling factor of the X-ray plasma in the core field microflares and in the extended loop is approximately 0.1, and (4) to release enough magnetic energy for a typical microflare (10^27 - 10^28 erg), a microflaring strand of sheared core field need expand and/or untwist by only a few percent at most. Finally, we point out that (1) the field configurations for strong coronal heating in our example active region (i.e., neutral-line core fields, many embedded in the feet of extended loops) are present in abundance in the magnetic network in quiet regions and coronal holes, and (2) it is known that many network bipoles do microflare and that many produce detectable coronal heating. We therefore propose that exploding sheared core fields are the drivers of most of the heating and dynamics of the solar atmosphere, ranging from the largest and most powerful coronal mass ejections and flares, to the vigorous microflaring and coronal heating in active regions, to the multitude of fine-scale explosive events in the magnetic network. The low-lysing exploding core fields in the network drive microflares, spicules, global coronal heating, and ,consequently, the solar wind.

Interpreting the Large Limb Eruption of July 9, 1982

A time series of K3 spectroheliograms taken at the Coimbra Observatory exhibits an erupting loop on the east limb on July 9, 1982 in active region NOAA 3804. The Goddard SMM Hard X-Ray Burst Spectrometer (HXRBS) observations taken during this period reveal a hard X-ray flare occurring just before the loop eruption is observed, and SMS-GOES soft X-ray observations reveal a strong long-duration event (LDE) following the impulsive phase of the flare. A Solwind coronagram exhibits a powerful coronal mass ejection (CME) associated with the erupting loop. Hα flare and prominence observations as well as centimeter and decimeter radio observations of the event are also reviewed. A large, north–south-oriented quiescent prominence reported within the upper part of the CME expansion region may play a role in the eruption as well. The spatial and temporal correlations among these observations are examined in the light of two different current models for prominence eruption and CME activation: (1) The CME is triggered by the observed hard X-ray impulsive flare. (2) The CME is not triggered by a flare, and the observed soft X-ray flare is an LDE due to reconnection within the CME ‘bubble’. It is concluded that this event is probably of a ‘mixed’ type that combines characteristics of models (1) and (2). The July 9 event is then compared to three other energetic CME and flare eruptions associated with the same active-region complex, all occurring in the period July 9 through September 4, 1982. It is noted that these four energetic events coincide with the final evolutionary phase of a long-lasting active-region complex, which is discussed in a companion paper (Bumba, Garcia, and Jordan, 1997). The paper concludes by addressing ‘the solar flare myth’ controversy in the light of this work.