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Editorial: Flux Rope Interaction With the Ambient Corona: From Jets to CMEs
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Microflaring in Low-Lying Core Fields and Extended Coronal Heating in the Quiet Sun
We have previously reported analyses of Yohkoh SXT data examining the relationship between the heating of extended coronal loops (both within and stemming from active regions) and microflaring in core fields lying along neutral lines near their footpoints (J. G. Porter, D. A. Falconer, and R. L. Moore 1998, in Solar Jets and Coronal Plumes, ed. T. Guyenne, ESA SP-421, and references therein). We found a surprisingly poor correlation of intensity variations in the extended loops with individual microflares in the compact heated areas at their feet, despite considerable circumstancial evidence linking the heating processes in these regions. Now, a study of Fe XII image sequences from SOHO EIT show that similar associations of core field structures with the footpoints of very extended coronal features can be found in the quiet Sun. The morphology is consistent with the finding of Wang et al. (1997, ApJ 484, L75) that polar plumes are rooted at sites of mixed polarity in the magnetic network. We find that the upstairs/downstairs intensity variations often follow the trend, identified in the active region observations, of a weak correspondence. Apparently much of the coronal heating in the extended loops is driven by a type of core field magnetic activity that is "cooler" than the events having the coronal signature of microflares, i.e., activity that results in little heating within the core fields themselves. This work was funded by the Solar Physics Branch of NASA's Office of Space Science through the SR&T Program and the SEC Guest Investigator Program.
Magnetic Untwisting in Solar Jets that Go into the Outer Corona in Polar Coronal Holes
We present results from 14 exceptionally high‐reaching large solar jets observed in the polar coronal holes. EUV movies from SDO/AIA show that each jet is similar to many other similar‐size and smaller jets that erupt in coronal holes, but each is exceptional in that it goes higher than most other jets, so high that it is observed in the outer corona beyond 2.2 R(sub Sun) in images from the SOHO/LASCO/C2 coronagraph. For these high‐reaching jets, we find: (1) the front of the jet transits the corona below 2.2 R(sub Sun) at a speed typically several times the sound speed; (2) each jet displays an exceptionally large amount of spin as it erupts; (3) in the outer corona, most jets display oscillatory swaying having an amplitude of a few degrees and a period of order 1 hour. We conclude that these jets are magnetically driven, propose that the driver is a magnetic‐untwisting wave that is grossly a large‐amplitude (i.e., nonlinear) torsional Alfven wave that is put into the reconnected open magnetic field in the jet by interchange reconnection as the jet erupts, and estimate from the measured spinning and swaying that the magnetic‐untwisting wave loses most of its energy in the inner corona below 2.2 R(sub Sun). From these results for these big jets, we reason that the torsional magnetic waves observed in Type‐II spicules should dissipate in the corona in the same way and could thereby power much of the coronal heating in coronal holes.
Persistent Doppler Shift Oscillations Observed with HINODE-EIS in the Solar Corona: Spectroscopic Signatures of Alfvenic Waves and Recurring Upflows
Using data obtained by the EUV Imaging Spectrometer on board Hinode, we have performed a survey of obvious and persistent (without significant damping) Doppler shift oscillations in the corona. We have found mainly two types of oscillations from February to April in 2007. One type is found at loop footpoint regions, with a dominant period around 10 minutes. They are characterized by coherent behavior of all line parameters (line intensity, Doppler shift, line width, and profile asymmetry), and apparent blueshift and blueward asymmetry throughout almost the entire duration. Such oscillations are likely to be signatures of quasi-periodic upflows (small-scale jets, or coronal counterpart of type-II spicules), which may play an important role in the supply of mass and energy to the hot corona. The other type of oscillation is usually associated with the upper part of loops. They are most clearly seen in the Doppler shift of coronal lines with formation temperatures between one and two million degrees. The global wavelets of these oscillations usually peak sharply around a period in the range of three to six minutes. No obvious profile asymmetry is found and the variation of the line width is typically very small. The intensity variation is often less than 2%. These oscillations are more likely to be signatures of kink/Alfv´en waves rather than flows. In a few cases, there seems to be a π/2 phase shift between the intensity and Doppler shift oscillations, which may suggest the presence of slow-mode standing waves according to wave theories. However, we demonstrate that such a phase shift could also be produced by loops moving into and out of a spatial pixel as a result of Alfv´enic oscillations. In this scenario, the intensity oscillations associated with Alfv´enic waves are caused by loop displacement rather than density change. These coronal waves may be used to investigate properties of the coronal plasma and magnetic field.
Evidence from IRIS that Sunspot Large Penumbral Jets Spin
Recent observations from Hinode (SOT/FG) revealed the presence of large penumbral jets (widths ≥ 500 km, larger than normal penumbral microjets, which have widths < 400 km) repeatedly occurring at the same locations in a sunspot penumbra, at the tail of a filament or where the tails of several penumbral filaments apparently converge (Tiwari et al. 2016, ApJ). These locations were observed to have mixed-polarity flux in Stokes-V images from SOT/FG. Large penumbral jets displayed direct signatures in AIA 1600, 304, 171, and 193 channels; thus they were heated to at least transition region temperatures. Because large jets could not be detected in AIA 94 Å, whether they had any coronal-temperature plasma remains unclear. In the present work, for another sunspot, we use IRIS Mg II k 2796 Å slit jaw images and spectra and magnetograms from Hinode SOT/FG and SOT/SP to examine: whether penumbral jets spin, similar to spicules and coronal jets in the quiet Sun and coronal holes; whether they stem from mixed-polarity flux; and whether they produce discernible coronal emission, especially in AIA 94 Å images. The few large penumbral jets for which we have IRIS spectra show evidence of spin. If these have mixed-polarity at their base, then they might be driven the same way as coronal jets and CMEs.
Very Narrow Coronal Mass Ejections Producing Solar Energetic Particles
Aims. Our main aim is to study the relationship between low-energy solar particles (energies below 1 MeV) and very narrow coronal mass ejections (“jets” with angular width ≤ 20°). Methods. For this purpose, we considered 125 very narrow coronal mass ejections (CMEs) from 1999 to 2003 that are potentially associated with low-energy solar particles (LESPs). These events were chosen on the basis of their source location. We studied only very narrow CMEs at the western limb, which are expected to have good magnetic connectivity with Earth. Results. We found 24 very narrow CMEs associated with energetic particles such as ions (protons and 3He), electrons, or both. We show that arrival times at Earth of energetic particles are consistent with onset times of the respective CMEs, and that in the same time intervals, there are no other potential sources of energetic particles. We also demonstrate statistical differences for the angular width distributions using the Kolmogorov–Smirnov test for angular widths for these 24 events. We consider a coherent sample of jets (mostly originating from boundaries of coronal holes) to identify properties of events that produce solar energetic particles (velocities, widths, and position angles). Our study presents a new approach and result: very narrow CMEs can generate low-energy particles in the vicinity of Earth without other activity on the Sun. The results could be very useful for space weather forecasting.
Editorial: Flux Rope Interaction With the Ambient Corona: From Jets to CMEs
Eruptive events within the Sun’s corona occur across a broad range of scales, from abundant small-scale jets to highly energetic coronal mass ejections (CMEs) (e.g., Webb and Howard, 2012; Raouafi et al., 2016; Kumar et al., 2021). Flux ropes have been understood to be a fundamental constituent of CMEs for many years, but it has only been more recently that their role in smaller eruptive events has become more appreciated (e.g., Sterling et al., 2015; Wyper et al., 2017). The key to understanding the differing morphology and nature of eruptions on these vastly differing scales is to understand the nature of the interaction between the flux ropes involved and the magnetic field of the surrounding corona. This Research Topic invited perspectives on (and examples of) flux rope eruptions across this broad range of scales, from formation to ejection, with the aim of highlighting commonalities and differences to aid in ultimately building a common framework for their understanding. Starting at the smallest scales, Schmieder presented a historically ordered review of jets and surges. The parallel improvements in instrumentation, physical insight and numerical simulations over time were highlighted along with the ways in which improvements in one area led to developments in another. Overall, jets of all forms are presented as the result of magnetic reconnection between two magnetic domains, with the reconnection involving a null point, bald patch separatrix or quasi-separatrix layer. In particular, jets with observed rotational motions often involve the transfer of twist from a small-scale filament or flux rope by reconnection across the separatrix.
Miniature Filament Eruptions and their Reconnections in X-Ray Jets: Evidence for a New Paradigm
We investigate the onset of approximately10 random X-ray jets observed by Hinode/XRT. Each jet was near the limb in a polar coronal hole, and showed a ``bright point'' in an edge of the base of the jet, as is typical for previously-observed X-ray jets. We examined SDO/AIA EUV images of each of the jets over multiple AIA channels, including 304 Ang, which detects chromospheric emissions, and 171, 193, and 211 Ang, which detect cooler-coronal emissions. We find the jets to result from eruptions of miniature (size less than approximately 10 arcsec) filaments from the bases of the jets. Much of the erupting-filament material forms a chromospheric-temperature jet. In the cool-coronal channels, often the filament appears in absorption and the jet in emission. The jet bright point forms at the location from which the miniature filament is ejected, analogous to the formation of a standard solar flare in the wake of the eruption of a typical larger-scale chromospheric filament. Thus these X-ray jets and their bright points are made by miniature filament eruptions. They are evidently produced the same way as an on-disk coronal jet we observed in Adams et al. (2014); that on-disk jet had no obvious emerging magnetic field in its base. We conclude that, for many jets, the standard idea of X-ray jets forming from reconnection between emerging flux and preexisting coronal field is incorrect. ACS and RLM were supported by funding from NASA/LWS, Hinode, and ISSI.
The Generation of Smooth High Speed Solar Wind from Plume-Interplume Mixing
Plumes and rays are magnetic field aligned density striations in coronal holes with different values of plasma beta. The overall plasma beta is very small in the low corona but exceeds unity beyond 15-20 solar radius. High speed solar wind reported beyond 0.3 AU is relatively smooth and uniform and known to originate from the much filamented coronal hole. Thus the obvious question is how to generate a smooth solar wind from seemingly filamentary structure. Hence one has to find a mechanism to substantiate this apparent observed (Ulysses) phenomenon. To do this we model plumes as jets (or wakes) of plasma emitted from the solar surface. The shear between a jet and its ambient is known to become unstable to the MHD Kelvin-Helmholtz ("KH") instability if the Alfven Mach number of the jet is greater than one and the uniform external magnetic field is small. Starting with a simple configuration we consider a jet of half thickness R, having uniform density and uniform internal magnetic field. The external medium has also a uniform density and uniform magnetic field. The jet is perturbed at the boundary with a linear amplitude and fixed frequency. We simulate the coronal jet using the 3D ZEUS code. The first results indicate the slab jet is unstable to the MHD KH instability at 5-10 solar radius for some angle of wave propagation. The propagating instability may smooth the filamented flow. It may also produce the entrained Alfvenic fluctuations observed by Ulysses in the high speed wind. We are at present determining the parameters which induce large growth rate. This may clarify the mystery behind the emergence of fast smooth solar wind from very filamentary structures in coronal holes. Also, using the dispersion relation already available for such a flow we obtain some general description of the instability criteria for the KH instability at a jet interface.
New Evidence on the Origin of Solar Wind Microstreams/Switchbacks
Microstreams are fluctuations in the solar wind speed and density associated with polarity-reversing folds in the magnetic field (also denoted switchbacks). Despite their long heritage, the origin of these microstreams/switchbacks remains poorly understood. For the first time, we investigated periodicities in microstreams during Parker Solar Probe (PSP) Encounter 10 to understand their origin. Our analysis was focused on the inbound corotation interval on 2021 November 19–21, while the spacecraft dove toward a small area within a coronal hole (CH). Solar Dynamics Observatory remote-sensing observations provide rich context for understanding the PSP in situ data. Extreme ultraviolet images from the Atmospheric Imaging Assembly reveal numerous recurrent jets occurring within the region that was magnetically connected to PSP during intervals that contained microstreams. The periods derived from the fluctuating radial velocities in the microstreams (approximately 3, 5, 10, and 20 minutes) are consistent with the periods measured in the emission intensity of the jetlets at the base of the CH plumes, as well as in larger coronal jets and in the plume fine structures. Helioseismic and Magnetic Imager magnetograms reveal the presence of myriad embedded bipoles, which are known sources of reconnection-driven jets on all scales. Simultaneous enhancements in the PSP proton flux and ionic ( 3 He, 4 He, Fe, O) composition during the microstreams further support the connection with jetlets and jets. In keeping with prior observational and numerical studies of impulsive coronal activity, we conclude that quasiperiodic jets generated by interchange/ breakout reconnection at CH bright points and plume bases are the most likely sources of the microstreams/ switchbacks observed in the solar wind.
The 18–19 March 2022 Series of 3He-Rich Events Observed By Solar Orbiter at 0.36 Au Compared With EUV, X-Ray, and Radio Observations
Context. During the first close perihelion pass of Solar Orbiter, a series of impulsive 3He-rich solar particle events was observed on 18–19 March 2022 from a distance of 0.36 au. In addition to the energetic particle, radio, and X-ray data from Solar Orbiter, the events were observed in radio and/or extreme ultraviolet by STEREO-A, SDO, Wind, and Parker Solar Probe. Aims. Observations of the event series along with remote sensing of flaring and radio emission with only small timing delays due to the close distance allow the association with energetic particles to be determined with much higher accuracy than previously possible from 1 au. Methods. By comparing the onsets of type-III bursts with the arrival of electrons of tens of keV at Solar Orbiter only a few minutes later, it can be seen that, overall, each of the more intense type-III bursts was associated with an electron and ion injection. Extreme ultraviolet data show that the times of the type-III bursts coincide with emission from a small (approximately Earth-sized) loop to the west of a nearby active region. Results. The energetic particle spectra and abundances show typical properties of impulsive 3He-rich flares and, when combined with the remote sensing observations, establish that the particle-accelerating mechanism in this series of events operates near the solar surface in association with magnetic loops, and in the absence of other phenomena such as jets and small coronal mass ejections.
A Rapid Sequence of Solar Energetic Particle Events Associated with a Series of Extreme-ultraviolet Jets: Solar Orbiter, STEREO-A, and Near-Earth Spacecraft Observations
A series of solar energetic electron (SEE) events was observed from 2022 November 9 to November 15 by Solar Orbiter, STEREO-A, and near-Earth spacecraft. At least 32 SEE intensity enhancements at energies >10 keV were clearly distinguishable in Solar Orbiter particle data, with 13 of them occurring on November 11. Several of these events were accompanied by 10 MeV proton and 2MeV nucleon−1 heavy-ion intensity enhancements. By combining remote-sensing and in situ data from the three viewpoints (Solar Orbiter and STEREO-A were ∼20° and ∼15° east of Earth, respectively), we determine that the origin of this rapid succession of events was a series of brightenings and jetlike eruptions detected in extreme ultraviolet (EUV) observations from the vicinity of two active regions. We find a close association between these EUV phenomena, the occurrence of hard X-ray flares, type III radio bursts, and the release of SEEs. For the most intense events, usually associated with extended EUV jets, the distance between the site of these solar eruptions and the estimated magnetic connectivity regions of each spacecraft with the Sun did not prevent the arrival of electrons at the three locations. The capability of jets to drive coronal fronts does not necessarily imply the observation of an SEE event. Two peculiar SEE events on November 9 and 14, observed only at electron energies 50 keV but rich in 1MeV nucleon−1 heavy ions, originated from slow-rising confined EUV emissions, for which the process resulting in energetic particle release to interplanetary space is unclear.
Observed Aspects of Reconnection in Solar Eruptions
Signatures of reconnection in major CME (coronal mass ejection)/flare eruptions and in coronal X-ray jets are illustrated and interpreted. The signatures are magnetic field lines and their feet that brighten in flare emission. CME/flare eruptions are magnetic explosions in which: 1. The field that erupts is initially a closed arcade. 2. At eruption onset, most of the free magnetic energy to be released is not stored in field bracketing a current sheet, but in sheared field in the core of the arcade. 3. The sheared core field erupts by a process that from its start or soon after involves fast tether-cutting reconnection at an initially small current sheet low in the sheared core field. If the arcade has oppositely-directed field over it, the eruption process from its start or soon after also involves fast breakout reconnection at an initially small current sheet between the arcade and the overarching field. These aspects are shown by the small area of the bright field lines and foot-point flare ribbons in the onset of the eruption. 4. At either small current sheet, the fast reconnection progressively unleashes the erupting core field to erupt with progressively greater force. In turn, the erupting core field drives the current sheet to become progressively larger and to undergo progressively greater fast reconnection in the explosive phase of the eruption, and the flare arcade and ribbons grow to become comparable to the pre-eruption arcade in lateral extent. In coronal X-ray jets: 1. The magnetic energy released in the jet is built up by the emergence of a magnetic arcade into surrounding unipolar "open" field. 2. A simple jet is produced when a burst of reconnection occurs at the current sheet between the arcade and the open field. This produces a bright reconnection jet and a bright reconnection arcade that are both much smaller in diameter that the driving arcade. 3. A more complex jet is produced when the arcade has a sheared core field and undergoes an ejective eruption in the manner of a miniature CME/flare eruption. The jet is then a combination of a miniature CME and the products of more widely distributed reconnection of the erupting arcade with the open field than in simple jets. Cartoons illustrating the above characteristics are presented along with representative examples of observed CME/flare eruptions and jets. The main point drawn to be drawn from the observations is that, for either a pre-eruption current sheet or a pre-simple-jet current sheet to remain quasi-static and stable against fast reconnection, it must remain much smaller in span than the driving arcade. Conversely, a current sheet comparable in span to the driving arcade can be made only dynamically, by eruption of the driving arcade, and continually undergoes massive fast reconnection.
MHD Modelling of Coronal Loops: Injection of High-Speed Chromospheric Flows
Context. Observations reveal a correspondence between chromospheric type II spicules and bright upward-moving fronts in the corona observed in the extreme-ultraviolet (EUV) band. However, theoretical considerations suggest that these flows are probably not the main source of heating in coronal magnetic loops. Aims. We investigate the propagation of high-speed chromospheric flows into coronal magnetic flux tubes and the possible production of emission in the EUV band. Methods. We simulated the propagation of a dense 104 K chromospheric jet upward along a coronal loop by means of a 2D cylindrical MHD model that includes gravity, radiative losses, thermal conduction, and magnetic induction. The jet propagates in a complete atmosphere including the chromosphere and a tenuous cool (approximately 0.8 MK) corona, linked through a steep transition region. In our reference model, the jet initial speed is 70 km per second, its initial density is 10(exp 11) per cubic centimeter, and the ambient uniform magnetic field is 10 G. We also explored other values of jet speed and density in 1D and different magnetic field values in 2D, as well as the jet propagation in a hotter (approximately 1.5 MK) background loop. Results. While the initial speed of the jet does not allow it to reach the loop apex, a hot shock-front develops ahead of it and travels to the other extreme of the loop. The shock front compresses the coronal plasma and heats it to about 10(exp 6) K. As a result, a bright moving front becomes visible in the 171 Angstrom channel of the SDO/AIA mission. This result generally applies to all the other explored cases, except for the propagation in the hotter loop. Conclusions. For a cool, low-density initial coronal loop, the post-shock plasma ahead of upward chromospheric flows might explain at least part of the observed correspondence between type II spicules and EUV emission excess.
Direct Evidence for the Dynamic Chromospheric Origin of Solar Coronal Plumes
Coronal plumes are long ray-like open structures in coronal holes, and have been considered as possible sources for the fast solar wind. Their origin in the largely unipolar coronal holes has long been a mystery. Earlier spectroscopic and imaging observations have revealed blue-shifted plasma and propagating disturbances (PDs) in plumes that are widely interpreted in terms of flows and/or propagating slow-mode waves, but these interpretations (flows vs waves)are under debate. Recently we discovered an important clue about plume internal structure: dynamic filamentary features called “plumelets”, which account for most of the plume emission. Here we present high-resolution observations from SDO/AIA and IRIS that revealed numerous quasiperiodic tiny jets (so-called “jetlets") associated with transient brightening and plasma heating at the chromospheric footpoints of the plumelets. By analogy to larger coronal jets, these jetlets are most likely produced within the plume base by magnetic reconnection between closed and open flux at a stressed 3D null point. The jetlet-associated brightenings are in phase with plumelet-associated PDs, and vary with a period of ∼3 to 5 minutes, which is remarkably consistent with the photospheric/chromospheric p-mode oscillation. This reconnection at the open-closed boundary in the chromosphere/transition region is likely modulated or driven by local manifestations of the global p-mode waves. We discuss how these quasiperiodic jetlets extend upward to become plumelets, contribute mass to the solar wind, and may be sources of switchbacks recently detected by the Parker Solar Probe.
Blowout Jets: Evidence from Hinode/XRT for X-Ray Jets Made by Blowout Eruption of the Emerging Bipole
Yamauchi et al (2004, ApJ, 605, 511) found that there are two structurally and dynamically distinct types of H macrospicules in polar coronal holes: single-column jet macrospicules and erupting-loop macrospicules. The structure and motion of the single-column jet macrospicules fit the standard Shibata reconnection picture for solar X-ray jets (Shibata et al 1992, PASJ, 44, L173). The form and motion of the erupting-loop macrospicules is reminiscent of the ejective eruption of the sheared-core-field flux rope in the filament-eruption birth of a bubble-type coronal mass ejection (CME). That roughly half of all polar H macrospicules were observed to be erupting-loop macrospicules suggests that there should be a corresponding large class of X-ray jets in which the emerging bipole at the base of the jet undergoes a blowout eruption as in a bubble-type CME, instead of staying closed as in the standard picture for X-ray jets. Along with a cartoon of the standard picture, we present a cartoon depicting the signatures to be expected of a blowout jet in high-resolution coronal X-ray movies such as from Hinode/XRT. From Hinode/XRT movies in polar coronal holes, we show: (1) examples of X-ray jets that fit the standard picture very well, and (2) other examples that do not fit the standard picture but do show signatures appropriate for blowout jets. These signatures are (1) a flare arcade inside the emerging bipole in addition to the flare arcade produced between the emerging bipole and the ambient high-reaching unipolar field by reconnection of these two fields as in the standard picture, and (2) in addition to the jet prong expected from the standard reconnection, a second jet prong or strand, one that could not be produced by the standard reconnection but could be produced by reconnection between the ambient unipolar field and one leg of an erupting core-field flux rope that has blown out the emerging bipole. We therefore infer that these "two pronged" jets are made by miniature versions of the sheared-core-bipole explosions that produce bubble-type CMEs. This work was funded by NASA s Science Mission Directorate through the Heliophysics Guest Investigators Program, the Hinode Project, and the Living With a Star Targeted Research and Technology Program.
Blowout Jets: Hinode X-Ray Jets that Don't Fit the Standard Model
Nearly half of all H-alpha macrospicules in polar coronal holes appear to be miniature filament eruptions. This suggests that there is a large class of X-ray jets in which the jet-base magnetic arcade undergoes a blowout eruption as in a CME, instead of remaining static as in most solar X-ray jets, the standard jets that fit the model advocated by Shibata. Along with a cartoon depicting the standard model, we present a cartoon depicting the signatures expected of blowout jets in coronal X-ray images. From Hinode/XRT movies and STEREO/EUVI snapshots in polar coronal holes, we present examples of (1) X-ray jets that fit the standard model, and (2) X-ray jets that do not fit the standard model but do have features appropriate for blowout jets. These features are (1) a flare arcade inside the jet-base arcade in addition to the small flare arcade (bright point) outside that standard jets have, (2) a filament of cool (T is approximately 80,000K) plasma that erupts from the core of the jetbase arcade, and (3) an extra jet strand that should not be made by the reconnection for standard jets but could be made by reconnection between the ambient unipolar open field and the opposite-polarity leg of the filament-carrying flux-rope core field of the erupting jet-base arcade. We therefore infer that these non-standard jets are blowout jets, jets made by miniature versions of the sheared-core-arcade eruptions that make CMEs