Magnetic Flux Cancellation Research Articles

The Origin of Major Solar Activity: Collisional Shearing between Nonconjugated Polarities of Multiple Bipoles Emerging within Active Regions

Abstract Active regions (ARs) that exhibit compact polarity inversion lines (PILs) are known to be very flare productive. However, the physical mechanisms behind this statistical inference have not been demonstrated conclusively. We show that such PILs can occur owing to the collision between two emerging flux tubes nested within the same AR. In such multipolar ARs, the flux tubes may emerge simultaneously or sequentially, each initially producing a bipolar magnetic region (BMR) at the surface. During each flux tube’s emergence phase, the magnetic polarities can migrate such that opposite polarities belonging to different BMRs collide, resulting in shearing and cancellation of magnetic flux. We name this process “collisional shearing” to emphasize that the shearing and flux cancellation develop owing to the collision. Collisional shearing is a process different from the known concept of flux cancellation occurring between polarities of a single bipole, a process that has been commonly used in many numerical models. High spatial and temporal resolution observations from the Solar Dynamics Observatory for two emerging ARs, AR 11158 and AR 12017, show the continuous cancellation of up to 40% of the unsigned magnetic flux of the smallest BMR, which occurs at the collisional PIL for as long as the collision persists. The flux cancellation is accompanied by a succession of solar flares and CMEs, products of magnetic reconnection along the collisional PIL. Our results suggest that the quantification of magnetic cancellation driven by collisional shearing needs to be taken into consideration in order to improve the prediction of solar energetic events and space weather.

A Giant Dark Channel across the Solar Equator Consisting of Two Filament Channels with Different Chiralities

Abstract Solar filaments are the largest magnetic structure that can be physically traced to the chromosphere. The structure and evolution of solar filaments are important for our understanding of solar atmosphere physics. In this work, we investigate a giant dark channel, which consists of two filament channels with different chiralities, crossing the solar equator. From 2016 April 22 to April 27, this giant dark channel occupied the solar disk. Within this giant channel, a filament channel with dextral chirality was detected in the northern hemisphere, and another filament channel with sinistral chirality was observed in the southern hemisphere. At the junction of the two filament channels, a cusp structure was observed associated with active region (AR) 12532 near the solar equator. The extrapolated three-dimensional magnetic fields reveal that this cusp structure was composed of two sets of field lines belonging to two different filament channels and was rooted in the AR positive-polarity fields. In addition, dark material flows from filaments in the two channels to the cusp structure were detected as well as flux emergence and cancellation around the cusp footpoints. On 2016 May 21, after a solar rotation, the cusp structure disappeared, and the giant dark channel broke in the middle, where another AR, 12546, emerged completely. We propose that the magnetic flux emergence and cancellation around the cusp region resulted in the disappearance of the cusp structure and the breaking of the giant dark channel.

Evidence of Twisting and Mixed-polarity Solar Photospheric Magnetic Field in Large Penumbral Jets: IRIS and Hinode Observations

Abstract A recent study using Hinode (Solar Optical Telescope/Filtergraph [SOT/FG]) data of a sunspot revealed some unusually large penumbral jets that often repeatedly occurred at the same locations in the penumbra, namely, at the tail of a penumbral filament or where the tails of multiple penumbral filaments converged. These locations had obvious photospheric mixed-polarity magnetic flux in Na i 5896 Stokes-V images obtained with SOT/FG. Several other recent investigations have found that extreme-ultraviolet (EUV)/X-ray coronal jets in quiet-Sun regions (QRs), in coronal holes (CHs), and near active regions (ARs) have obvious mixed-polarity fluxes at their base, and that magnetic flux cancellation prepares and triggers a minifilament flux-rope eruption that drives the jet. Typical QR, CH, and AR coronal jets are up to 100 times bigger than large penumbral jets, and in EUV/X-ray images they show a clear twisting motion in their spires. Here, using Interface Region Imaging Spectrograph (IRIS) Mg ii k λ2796 SJ images and spectra in the penumbrae of two sunspots, we characterize large penumbral jets. We find redshift and blueshift next to each other across several large penumbral jets, and we interpret these as untwisting of the magnetic field in the jet spire. Using Hinode/SOT (FG and SP) data, we also find mixed-polarity magnetic flux at the base of these jets. Because large penumbral jets have a mixed-polarity field at their base and have a twisting motion in their spires, they might be driven the same way as QR, CH, and AR coronal jets.

A Blowout Jet Associated with One Obvious Extreme-ultraviolet Wave and One Complicated Coronal Mass Ejection Event

Abstract In this paper, we present a detailed analysis of a coronal blowout jet eruption that was associated with an obvious extreme-ultraviolet (EUV) wave and one complicated coronal mass ejection (CME) event based on the multiwavelength and multi-view-angle observations from the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory. It is found that the triggering of the blowout jet was due to the emergence and cancellation of magnetic fluxes on the photosphere. During the rising stage of the jet, the EUV wave appeared just ahead of the jet top, lasting about 4 minutes and at a speed of 458–762 km s−1. In addition, obvious dark material is observed along the EUV jet body, which confirms the observation of a mini-filament eruption at the jet base in the chromosphere. Interestingly, two distinct but overlapped CME structures can be observed in corona together with the eruption of the blowout jet. One is a narrow jet shape, while the other one is a bubble shape. The jet-shaped component was unambiguously related to the outwardly running jet itself, while the bubble-like one might either be produced due to the reconstruction of the high coronal fields or by the internal reconnection during the mini-filament ejection according to the double-CME blowout jet model first proposed by Shen et al., suggesting more observational evidence should be supplied to clear the current ambiguity based on large samples of blowout jets in future studies.

Physical Processes Involved in the EUV “Surge” Event of 9 May 2012

We study an EUV confined ejection observed on 09 May 2012 in active region (AR) NOAA 11476. For the analysis we use observations in multiple wavelengths (EUV, X-rays, H$\alpha$, and magnetograms) from a variety of ground-based and space instruments. The magnetic configuration showed the presence of two rotating bipoles, with decreasing magnetic flux, within the following polarity of the AR. This evolution was present along some tens of hours before the studied event and continued even later. A minifilament with a length of $\approx 30 \arcsec$ lay along the photospheric inversion line of the largest bipole. The minifilament was observed to erupt accompanied by an M4.7 flare (SOL20120509T12:23:00). Consequently, dense material, as well as twist, was injected along closed loops in the form of a very broad ejection whose morphology resembles that of typical H$\alpha$ surges. We conclude that the flare and eruption can be explained as due to two reconnection processes, one occurring below the erupting minifilament and another one above it. This second process injects the minifilament plasma within the reconnected closed loops linking the main AR polarities. Analyzing the magnetic topology using a force-free model of the coronal field, we identify the location of quasi-separatix layers (QSLs), where reconnection is prone to occur, and present a detailed interpretation of the chromospheric and coronal eruption observations. In particular, this event, contrary to what has been proposed in several models explaining surges and/or jets, is not originated by magnetic flux emergence but by magnetic flux cancellation accompanied by the rotation of the bipoles. In fact, the conjunction of these two processes, flux cancellation and bipole rotations, is at the origin of a series of events, homologous to the one we analyze in this article, that occurred in AR 11476 from 08 to 10 May 2012.

A Modified Bridge Switch-Type Flux-Coupling Nonsuperconducting Fault Current Limiter for Suppression of Fault Transients

This paper proposes a modified bridge switch-type flux-coupling nonsuperconducting fault current limiter (BSFC-NSFCL) for suppressing the fault current and voltage sag. A flux-coupling reactor and a bidirectional bridge switch are combined to perform the functions of steady-state line current sharing and fault current suppression. The modified BSFC-NSFCL mainly utilizes the magnetic flux cancellation effect to make the limiter behave as a short circuit on the circuit during normal operation. Hence, there is almost no impact on the power system when the limiter is used. When a fault event occurs, the bridge switch turns off immediately, and then, the magnetic flux cancellation effect disappears. Thus, the impedance of primary coil inserts into the circuit to restrict the fault current and voltage sag phenomena. Once the fault is removed, the bridge switch turns on again, and the BSFC-NSFCL recovers to the normal operation. The modified NSFCL is more cost-effective and easy to be implemented than the flux-coupling superconducting fault current limiter. Theoretical analysis for the BSFC-NSFCL has been fully developed and proven by MATLAB software. Finally, the analytical, simulated, and experimental results have been carried out to verify the feasibility and performance of the proposed BSFC-NSFCL.

IRIS and SDO Observations of Solar Jetlets Resulting from Network-edge Flux Cancelation

Abstract Recent observations show that the buildup and triggering of minifilament eruptions that drive coronal jets result from magnetic flux cancelation at the neutral line between merging majority- and minority-polarity magnetic flux patches. We investigate the magnetic setting of 10 on-disk small-scale UV/EUV jets (jetlets, smaller than coronal X-ray jets but larger than chromospheric spicules) in a coronal hole by using IRIS UV images and SDO/AIA EUV images and line-of-sight magnetograms from SDO/HMI. We observe recurring jetlets at the edges of magnetic network flux lanes in the coronal hole. From magnetograms coaligned with the IRIS and AIA images, we find, clearly visible in nine cases, that the jetlets stem from sites of flux cancelation proceeding at an average rate of ∼1.5 × 1018 Mx hr−1, and show brightenings at their bases reminiscent of the base brightenings in larger-scale coronal jets. We find that jetlets happen at many locations along the edges of network lanes (not limited to the base of plumes) with average lifetimes of 3 minutes and speeds of 70 km s−1. The average jetlet-base width (4000 km) is three to four times smaller than for coronal jets (∼18,000 km). Based on these observations of 10 obvious jetlets, and our previous observations of larger-scale coronal jets in quiet regions and coronal holes, we infer that flux cancelation is an essential process in the buildup and triggering of jetlets. Our observations suggest that network jetlet eruptions might be small-scale analogs of both larger-scale coronal jets and the still-larger-scale eruptions producing CMEs.

Eruption of a multi-flux-rope system in solar active region 12673 leading to the two largest flares in Solar Cycle 24

Context. Solar active region (AR) 12673 in 2017 September produced the two largest flares in Solar Cycle 24: the X9.3 flare on September 6 and the X8.2 flare on September 10. Aims. We attempt to investigate the evolutions of the two large flares and their associated complex magnetic system in detail. Methods. Combining observations from the Solar Dynamics Observatory and results of nonlinear force-free field (NLFFF) modeling, we identify various magnetic structures in the AR core region and examine the evolution of these structures during the flares. Results. Aided by the NLFFF modeling, we identify a double-decker flux rope configuration above the polarity inversion line (PIL) in the AR core region. The north ends of these two flux ropes were rooted in a negative- polarity magnetic patch, which began to move along the PIL and rotate anticlockwise before the X9.3 flare on September 6. The strong shearing motion and rotation contributed to the destabilization of the two magnetic flux ropes, of which the upper one subsequently erupted upward due to the kink-instability. Then another two sets of twisted loop bundles beside these ropes were disturbed and successively erupted within five minutes like a chain reaction. Similarly, multiple ejecta components were detected as consecutively erupting during the X8.2 flare occurring in the same AR on September 10. We examine the evolution of the AR magnetic fields from September 3 to 6 and find that five dipoles emerged successively at the east of the main sunspot. The interactions between these dipoles took place continuously, accompanied by magnetic flux cancellations and strong shearing motions. Conclusions. In AR 12673, significant flux emergence and successive interactions between the different emerging dipoles resulted in a complex magnetic system, accompanied by the formations of multiple flux ropes and twisted loop bundles. We propose that the eruptions of a multi-flux-rope system resulted in the two largest flares in Solar Cycle 24.

Study of two-stage coronal jet associated with a C1.4 class solar flare

We study an active region coronal jet that evolved from southward of a major sunspot of NOAA AR12178 on 04 October 2014. This jet is associated with an onset of the GOES C1.4 flare. We use SDO/AIA, SDO/HMI, GONG \(H\upalpha\) and GOES data for analysing the observed event. We term this jet as a two-stage confined eruption of the plasma. In the first stage, some plasma erupts above the compact flaring region. In the second stage, this eruptive jet plasma and associated magnetic field lines interact with another set of distinct magnetic field lines present in its south-east direction. This creates an X-point region, where the second stage of the jet eruption is deflected above it on a curvilinear path into overlying corona. The lower part of the jet is followed by a cool surge eruption, which is visible only in \(H{\upalpha}\) emissions. The magnetic flux cancellation at the footpoint causes the triggering of C-class flare eruption. This flare energy release further triggers first stage of the coronal jet eruption. The second stage of the jet eruption is a consequence of an interaction of two distinct sets of magnetic field lines in the overlying corona. The first stage of the coronal jet and co-spatial but lagging cool surge may have common origin due to the reconnection generated heating pulses. This complex evolution of the coronal jet involves flare heating induced first stage plasma eruption, guiding of jet’s material above a junction of two distinct sets of field lines in the corona, and intra-relationship with cool surge. In effect, it imposes rigid constraints on the existing jet models.

Magnetic Flux Cancelation as the Buildup and Trigger Mechanism for CME-producing Eruptions in Two Small Active Regions

Abstract We follow two small, magnetically isolated coronal mass ejection (CME)-producing solar active regions (ARs) from the time of their emergence until several days later, when their core regions erupt to produce the CMEs. In both cases, magnetograms show: (a) following an initial period where the poles of the emerging regions separate from each other, the poles then reverse direction and start to retract inward; (b) during the retraction period, flux cancelation occurs along the main neutral line of the regions; (c) this cancelation builds the sheared core field/flux rope that eventually erupts to make the CME. In the two cases, respectively 30% and 50% of the maximum flux of the region cancels prior to the eruption. Recent studies indicate that solar coronal jets frequently result from small-scale filament eruptions, with those “minifilament” eruptions also being built up and triggered by cancelation of magnetic flux. Together, the small-AR eruptions here and the coronal jet results suggest that isolated bipolar regions tend to erupt when some threshold fraction, perhaps in the range of 50%, of the region's maximum flux has canceled. Our observed erupting filaments/flux ropes form at sites of flux cancelation, in agreement with previous observations. Thus, the recent finding that minifilaments that erupt to form jets also form via flux cancelation is further evidence that minifilaments are small-scale versions of the long-studied full-sized filaments.

A Cancellation Nanoflare Model for Solar Chromospheric and Coronal Heating

Abstract Nanoflare models for heating the solar corona usually assume magnetic braiding and reconnection as the source of the energy. However, recent observations at record spatial resolution from the Sunrise balloon mission suggest that photospheric magnetic flux cancellation is much more common than previously realized. We therefore examine the possibility of three-dimensional reconnection driven by flux cancellation as a cause of chromospheric and coronal heating. In particular, we estimate how the heights and amount of energy release produced by flux cancellation depend on flux size, flux cancellation speed, and overlying field strength.

Observational Evidence of Magnetic Reconnection Associated with Magnetic Flux Cancellation

Abstract Using high spatial and temporal data from the Solar Dynamics Observatory (SDO) and the Interface Region Imaging Spectrograph (IRIS), several observational signatures of magnetic reconnection in the course of magnetic flux cancellation are presented, including two loop–loop interaction processes, multiple plasma blob ejections, and a sheet-like structure that appeared above the flux cancellation sites with a Y-shaped and an inverted Y-shaped end. The IRIS 1400 Å observations show that the plasma blobs were ejected from the tip of the Y-shaped ends of the sheet-like structure. Obvious photospheric magnetic flux cancellation occurred after the first loop–loop interaction and continued until the end of the observation. Complemented by the nonlinear force-free field extrapolation, we found that two sets of magnetic field lines, which revealed an X-shaped configuration, aligned well with the interacted coronal loops. Moreover, a magnetic null point was found to be situated at about 0.9 Mm height, which was right above the flux cancellation sites and located between the two sets of magnetic field lines. These results suggest that the flux cancellation might be a result of the submergence of magnetic field lines following a magnetic reconnection that occurs in the lower atmosphere of the Sun, and the ejected plasma blobs should be plasmoids created in the sheet-like structure due to the tearing-mode instability. This observation reveals a detailed magnetic field structure and a dynamic process above the flux cancellation sites and will help us to understand magnetic reconnection in the lower atmosphere of the Sun.

Critical Magnetic Field Strengths for Solar Coronal Plumes in Quiet Regions and Coronal Holes?

Abstract Coronal plumes are bright magnetic funnels found in quiet regions (QRs) and coronal holes (CHs). They extend high into the solar corona and last from hours to days. The heating processes of plumes involve dynamics of the magnetic field at their base, but the processes themselves remain mysterious. Recent observations suggest that plume heating is a consequence of magnetic flux cancellation and/or convergence at the plume base. These studies suggest that the base flux in plumes is of mixed polarity, either obvious or hidden in Solar Dynamics Observatory (SDO)/HMI data, but do not quantify it. To investigate the magnetic origins of plume heating, we select 10 unipolar network flux concentrations, four in CHs, four in QRs, and two that do not form a plume, and track plume luminosity in SDO/AIA 171 Å images along with the base flux in SDO/HMI magnetograms, over each flux concentration’s lifetime. We find that plume heating is triggered when convergence of the base flux surpasses a field strength of ∼200–600 G. The luminosity of both QR and CH plumes respond similarly to the field in the plume base, suggesting that the two have a common formation mechanism. Our examples of non-plume-forming flux concentrations, reaching field strengths of 200 G for a similar number of pixels as for a couple of our plumes, suggest that a critical field might be necessary to form a plume but is not sufficient for it, thus advocating for other mechanisms, e.g., flux cancellation due to hidden opposite-polarity field, at play.

Spectroscopic and imaging observations of small-scale reconnection events

We present spectroscopic and imaging observations of small-scale reconnection events on the Sun. Using the Interface Region Imaging Spectrograph (IRIS) observations, one reconnection event is first detected as IRIS jets with fast bi-directional velocities in the chromosphere and transition region, which are identified as non-Gaussian broadenings with two extended wings in the line profiles of Si iv, C ii, and Mg ii k. The magnetograms under the IRIS jets from Helioseismic and Magnetic Images exhibit magnetic flux cancellation simultaneously, supporting that the IRIS jets are driven by magnetic reconnection. The Atmospheric Imaging Assembly images also show an extreme ultraviolet (EUV) brightening which is shortly after the underlying IRIS jets, i.e., in the 131 A, 171 A, 193 A, 211 A, and 94 A channels, implying that the over-lying EUV brightening in the corona is caused by the IRIS jets in the chromosphere and transition region. We also find another three reconnection events which show the same features during this IRIS observation. Our observational results suggest that the small-scale reconnection events might contribute to the coronal heating. The new result is that the process of magnetic reconnection is detected from the photosphere through chromosphere and transition region to the corona.

Nature of the energy source powering solar coronal loops driven by nanoflares

Context. Magnetic energy is required to heat the corona, the outer atmosphere of the Sun, to millions of degrees. Aims. We study the nature of the magnetic energy source that is probably responsible for the brightening of coronal loops driven by nanoflares in the cores of solar active regions. Methods. We consider observations of two active regions (ARs), 11890 and 12234, in which nanoflares have been detected. To this end, we use ultraviolet (UV) and extreme ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) for coronal loop diagnostics. These images are combined with the co-temporal line-of-sight magnetic field maps from the Helioseismic and Magnetic Imager (HMI) onboard SDO to investigate the connection between coronal loops and their magnetic roots in the photosphere. Results. The core of these ARs exhibit loop brightening in multiple EUV channels of AIA, particularly in its 9.4 nm filter. The HMI magnetic field maps reveal the presence of a complex mixed polarity magnetic field distribution at the base of these loops. We detect the cancellation of photospheric magnetic flux at these locations at a rate of about 1015 Mx s−1. The associated compact coronal brightenings directly above the cancelling magnetic features are indicative of plasma heating due to chromospheric magnetic reconnection. Conclusions. We suggest that the complex magnetic topology and the evolution of magnetic field, such as flux cancellation in the photosphere and the resulting chromospheric reconnection, can play an important role in energizing active region coronal loops driven by nanoflares. Our estimate of magnetic energy release during flux cancellation in the quiet Sun suggests that chromospheric reconnection can also power the quiet corona.

Onset of the Magnetic Explosion in Solar Polar Coronal X-Ray Jets

Abstract We follow up on the Sterling et al. discovery that nearly all polar coronal X-ray jets are made by an explosive eruption of a closed magnetic field carrying a miniature filament in its core. In the same X-ray and EUV movies used by Sterling et al., we examine the onset and growth of the driving magnetic explosion in 15 of the 20 jets that they studied. We find evidence that (1) in a large majority of polar X-ray jets, the runaway internal/tether-cutting reconnection under the erupting minifilament flux rope starts after both the minifilament’s rise and the spire-producing external/breakout reconnection have started; and (2) in a large minority, (a) before the eruption starts, there is a current sheet between the explosive closed field and the ambient open field, and (b) the eruption starts with breakout reconnection at that current sheet. The variety of event sequences in the eruptions supports the idea that the magnetic explosions that make polar X-ray jets work the same way as the much larger magnetic explosions that make a flare and coronal mass ejection (CME). That idea and recent observations indicating that magnetic flux cancellation is the fundamental process that builds the field in and around the pre-jet minifilament and triggers that field’s jet-driving explosion together suggest that flux cancellation inside the magnetic arcade that explodes in a flare/CME eruption is usually the fundamental process that builds the explosive field in the core of the arcade and triggers that field’s explosion.

Magnetic Reconnection at the Earliest Stage of Solar Flux Emergence

Abstract On 2016 September 20, the Interface Region Imaging Spectrograph observed an active region during its earliest emerging phase for almost 7 hr. The Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory observed continuous emergence of small-scale magnetic bipoles with a rate of ∼1016 Mx s−1. The emergence of magnetic fluxes and interactions between different polarities lead to the frequent occurrence of ultraviolet (UV) bursts, which exhibit as intense transient brightenings in the 1400 Å images. In the meantime, discrete small patches with the same magnetic polarity tend to move together and merge, leading to the enhancement of the magnetic fields and thus the formation of pores (small sunspots) at some locations. The spectra of these UV bursts are characterized by the superposition of several chromospheric absorption lines on the greatly broadened profiles of some emission lines formed at typical transition region temperatures, suggesting heating of the local materials to a few tens of thousands of kelvin in the lower atmosphere by magnetic reconnection. Some bursts reveal blue- and redshifts of ∼100 km s−1 at neighboring pixels, indicating the spatially resolved bidirectional reconnection outflows. Many such bursts appear to be associated with the cancellation of magnetic fluxes with a rate of the order of ∼1015 Mx s−1. We also investigate the three-dimensional magnetic field topology through a magnetohydrostatic model and find that a small fraction of the bursts are associated with bald patches (magnetic dips). Finally, we find that almost all bursts are located in regions of large squashing factor at the height of ∼1 Mm, reinforcing our conclusion that these bursts are produced through reconnection in the lower atmosphere.

Magnetic Flux Cancelation as the Trigger of Solar Coronal Jets in Coronal Holes

Abstract We investigate in detail the magnetic cause of minifilament eruptions that drive coronal-hole jets. We study 13 random on-disk coronal-hole jet eruptions, using high-resolution X-ray images from the Hinode/X-ray telescope(XRT), EUV images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), and magnetograms from the SDO/Helioseismic and Magnetic Imager (HMI). For all 13 events, we track the evolution of the jet-base region and find that a minifilament of cool (transition-region-temperature) plasma is present prior to each jet eruption. HMI magnetograms show that the minifilaments reside along a magnetic neutral line between majority-polarity and minority-polarity magnetic flux patches. These patches converge and cancel with each other, with an average cancelation rate of ∼0.6 × 1018 Mx hr−1 for all 13 jets. Persistent flux cancelation at the neutral line eventually destabilizes the minifilament field, which erupts outward and produces the jet spire. Thus, we find that all 13 coronal-hole-jet-driving minifilament eruptions are triggered by flux cancelation at the neutral line. These results are in agreement with our recent findings for quiet-region jets, where flux cancelation at the underlying neutral line triggers the minifilament eruption that drives each jet. Thus, from that study of quiet-Sun jets and this study of coronal-hole jets, we conclude that flux cancelation is the main candidate for triggering quiet-region and coronal-hole jets.

Multiple Solar Jets from NOAA AR 12644

AbstractWe present here the observations of solar jets observed on April 04, 2017 from NOAA active region (AR) 12644 using high temporal and spatial resolution AIA instrument. We have observed around twelve recurring jets during the whole day. Magnetic flux emergence and cancellation have been observed at the jet location. The multi-band observations evidenced that these jets were triggered due to the magnetic reconnection at low coronal null–point.

Untwisting Jets Related to Magnetic Flux Cancellation

Abstract The rotational motion of solar jets is believed to be a signature of the untwisting process resulting from magnetic reconnection, which takes place between twisted closed magnetic loops (i.e., magnetic flux ropes) and open magnetic field lines. The identification of the pre-existing flux rope, and the relationship between the twist contained in the rope and the number of turns the jet experiences, are then vital in understanding the jet-triggering mechanism. In this paper, we will perform a detailed analysis of imaging, spectral, and magnetic field observations of four homologous jets, among which the fourth one releases a twist angle of 2.6π. Nonlinear force-free field extrapolation of the photospheric vector magnetic field before the jet eruption presents a magnetic configuration with a null point between twisted and open fields—a configuration highly in favor of the eruption of solar jets. The fact that the jet rotates in the opposite sense of handness to the twist contained in the pre-eruption photospheric magnetic field confirms the unwinding of the twist by the jet’s rotational motion. The temporal relationship between jets’ occurrence and the total negative flux at their source region, together with the enhanced magnetic submergence term of the photospheric Poynting flux, shows that these jets are highly associated with local magnetic flux cancellation.