Observational Evidence Of Magnetic Reconnection Research Articles

Splitting and Eruption of an Active Region Filament Caused by Magnetic Reconnection

To gain a deeper understanding of the intricate process of filament eruption, we present a case study of a filament splitting and erupting by using multiwavelength data of the Solar Dynamics Observatory. It is found that the magnetic reconnection between the filament and the surrounding magnetic loops resulted in the formation of two new filaments, which erupted successively. The observational evidence of magnetic reconnection, such as the obvious brightening at the junction of two different magnetic structures, the appearance of a bidirectional jet, and subsequent filament splitting, were clearly observed. Even though the two newly formed filaments experienced failed eruptions, three obvious dimmings were observed at the footpoints of the filaments during their eruptions. Based on these observations, it is suggested that magnetic reconnection is the trigger mechanism for the splitting of the original filament and the subsequent eruption of the newly formed filaments. Furthermore, the process of filament splitting dominated by magnetic reconnection can shed light on the explanation of double-decker filament formation.

Solar Wind—Magnetosphere Coupling During Radial Interplanetary Magnetic Field Conditions: Simultaneous Multi‐Point Observations

AbstractIn‐situ spacecraft missions are powerful assets to study processes that occur in space plasmas. One of their main limitations, however, is extrapolating such local measurements to the global scales of the system. To overcome this problem at least partially, multi‐point measurements can be used. There are several multi‐spacecraft missions currently operating in the Earth's magnetosphere, and the simultaneous use of the data collected by them provides new insights into the large‐scale properties and evolution of magnetospheric plasma processes. In this work, we focus on studying the Earth's magnetopause (MP) using a conjunction between the Magnetospheric Multiscale and Cluster fleets, when both missions skimmed the MP for several hours at distant locations during radial interplanetary magnetic field (IMF) conditions. The observed MP positions as a function of the evolving solar wind conditions are compared to model predictions of the MP. We observe an inflation of the magnetosphere (∼0.7 RE), consistent with magnetosheath pressure decrease during radial IMF conditions, which is less pronounced on the flank (0.2 RE). There is observational evidence of magnetic reconnection in the subsolar region for the whole encounter, and in the dusk flank for the last portion of the encounter, suggesting that reconnection was extending more than 15 RE. However, reconnection jets were not always observed, suggesting that reconnection was patchy, intermittent or both. Shear flows reduce the reconnection rate up to ∼30% in the dusk flank according to predictions, and the plasma β enhancement in the magnetosheath during radial IMF favors reconnection suppression by the diamagnetic drift.

Observational Evidence of Magnetic Reconnection in the Terrestrial Foreshock Region

Abstract Electron heating/acceleration in the foreshock, by which electrons may be energized beyond thermal energies prior to encountering the bow shock, is very important for the bow shock dynamics. And then these electrons would be more easily injected into a process like diffusive shock acceleration. Many mechanisms have been proposed to explain electrons heating/acceleration in the foreshock. Magnetic reconnection is one possible candidate. Taking advantage of the Magnetospheric Multiscale mission, we present two magnetic reconnection events in the dawnside and duskside ion foreshock region, respectively. Super-Alfvénic electron outflow, demagnetization of the electrons and the ions, and crescent electron distributions in the plane perpendicular to the magnetic field are observed in the sub-ion-scale current sheets. Moreover, strong energy conversion from the fields to the plasmas and significant electron temperature enhancement are observed. Our observations provide direct evidence that magnetic reconnection could occur in the foreshock region and heat/accelerate the electrons therein.

Magnetic Reconnection Within the Boundary Layer of a Magnetic Cloud in the Solar Wind

AbstractThe twisted local magnetic field at the front or rear regions of the magnetic clouds (MCs) associated with interplanetary coronal mass ejections (ICMEs) is often nearly opposite to the direction of the ambient interplanetary magnetic field. There is also observational evidence for magnetic reconnection (MR) outflows occurring within the boundary layers of MCs. In this study, a MR event located at the western flank of the MC occurring on October 3, 2000 is studied in detail. Both the large‐scale geometry of the helical MC and the MR outflow structure are scrutinized in a detailed multipoint study. The ICME sheath is of hybrid propagation‐expansion type. Here, the freshly reconnected open field lines are expected to slip slowly over the MC resulting in plasma mixing at the same time. As for MR, the current sheet geometry and the vertical motion of the outflow channel between ACE‐Geotail‐WIND spacecraft were carefully studied and tested. The main findings on MR include (a) first‐time observation of non‐Petschek‐type slow‐shock‐like discontinuities in the inflow regions; (b) observation of turbulent Hall magnetic field associated with a Lorentz‐force‐deflected electron jet; (c) acceleration of protons by reconnection electric field and their back‐scatter from the slow‐shock‐like discontinuity; (d) observation of relativistic electron near the MC inflow boundary/separatrix; these electron populations can presumably appear as a result of nonadiabatic acceleration, gradient B drift, and via acceleration in the electrostatic potential well associated with the Hall current system; and (e) observation of Doppler‐shifted ion‐acoustic and Langmuir waves in the MC inflow region.

Observational evidence of magnetic reconnection in a coronal bright point

Magnetic reconnection is considered to be the fundamental process by which magnetic energy is converted into plasma or particle kinetic energy. Magnetic reconnection is a widely applied physics model to explain the solar eruption events, such as coronal bright points (CBPs). Meanwhile, it is an usual way of the solar physics research to look for the observational evidences of magnetic reconnection in the solar eruption events in order to support the model. In this paper, we have explored the evidences of magnetic reconnection in a CBP observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) at NOAA No. 11163 on 2011 March 5. Our observations show that this event is a small-scale loop system in active regions that have similar size as a traditional CBP and it might shed light on the physics of a traditional CBP. This CBP is bright in all nine AIA wavelengths and displays a flaring development with three bursts intermittently. Each burst exhibits a pair of bi-directional jets almost along a line. They originate from the same position (CBP core), then move in the opposite directions. Our findings are well consistent with the magnetic reconnection process by which the bi-directional plasma outflows are produced and radiate the bi-directional jets detected by SDO/AIA. These facts further support the conclusion that the CBP is produced by the magnetic reconnection process.

Multiband Study of a Bidirectional Jet Occurred in the Upper Chromosphere

AbstractWe present a study of a jet observed by the Solar Dynamics Observatory (SDO) and the Interface Region Imaging Spectrograph (IRIS), which provide high spatial‐temporal resolution observational data of (extreme) ultraviolet images, spectra, and magnetograms. The jet was observed in multiple bands of AIA and manifested clear bidirectional flows in observations. The emission profiles of the Si IV 1402 Å line of the jet exhibited non‐Gaussian features and double‐peaked spectra, with the Doppler velocity and the nonthermal velocity up to 100 and 160 km s , respectively. The plasma flows of the jet projected on the sky plane and in the line of sight (LOS) are the typical observational evidence of magnetic reconnection. The EM loci curves indicated that the plasma contains multi‐temperature components. The result deduced from the DEM method and changes in intensity of several spectral lines imply that the temperature of the plasma in the jet is heated to at least K. The electron density is about cm according to the intensity ratios of the O IV 1399.77/1401.16 Å doublet and Si IV 1402.77/O IV 1401.16 Å lines. Via different approaches, we reached the conclusion that the jet occurred in the upper chromosphere. Investigating the magnetograms in the period when the jet appeared, we suggest that the jet results from the magnetic reconnection between the moving magnetic structure and the magnetic field nearby.

Observational Evidence of Magnetic Reconnection in the Terrestrial Bow Shock Transition Region

AbstractWe report evidence of magnetic reconnection in the transition region of the Earth's bow shock when the angle between the shock normal and the immediate upstream magnetic field is 65°. An ion‐skin‐depth‐scale current sheet exhibits the Hall current and field pattern, electron outflow jet, and enhanced energy conversion rate through the nonideal electric field, all consistent with a reconnection diffusion region close to the X‐line. In the diffusion region, electrons are modulated by electromagnetic waves. An ion exhaust with energized field‐aligned ions and electron parallel heating are observed in the same shock transition region. The energized ions are more separated from the inflowing ions in velocity above the current sheet than below, possibly due to the shear flow between the two inflow regions. The observation suggests that magnetic reconnection may contribute to shock energy dissipation.

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.

Observational Evidence of Magnetic Reconnection for Brightenings and Transition Region Arcades in IRIS Observations

Abstract By using a new method of forced-field extrapolation, we study the emerging flux region AR11850 observed by the Interface Region Imaging Spectrograph and Solar Dynamical Observatory. Our results suggest that the bright points (BPs) in this emerging region exhibit responses in lines formed from the upper photosphere to the transition region, which have relatively similar morphologies. They have an oscillation of several minutes according to the Atmospheric Imaging Assembly data at 1600 and 1700 Å. The ratio between the BP intensities measured in 1600 and 1700 Å filtergrams reveals that these BPs are heated differently. Our analysis of the Helioseismic and Magnetic Imager vector magnetic field and the corresponding topology in AR11850 indicates that the BPs are located at the polarity inversion line and most of them are related to magnetic reconnection or cancelation. The heating of the BPs might be different due to different magnetic topology. We find that the heating due to the magnetic cancelation would be stronger than the case of bald patch reconnection. The plasma density rather than the magnetic field strength could play a dominant role in this process. Based on physical conditions in the lower atmosphere, our forced-field extrapolation shows consistent results between the bright arcades visible in slit-jaw image 1400 Å and the extrapolated field lines that pass through the bald patches. It provides reliable observational evidence for testing the mechanism of magnetic reconnection for the BPs and arcades in the emerging flux region, as proposed in simulation studies.

Solar activities observed with the New Vacuum Solar Telescope

AbstractBased on the New Vacuum Solar Telescope observations, some new results about the solar activities are obtained. (1) In the Hα line, a flux rope tracked by filament activation is detected for the first time. There may exist some mild heating during the filament activation. (2) The direct observations illustrate the mechanism of confined flares, i.e., the flares are triggered by magnetic reconnection between the emerging loops and the pre-existing loops and prevented from being eruptive by the overlying loops. (3) The solid observational evidence of magnetic reconnection between two sets of small-scale loops is reported. The successive slow reconnection changes the conditions around the reconnection area and leads to the rapid reconnection. (4) An ensemble of oscillating bright features rooted in a light bridge is observed and given a new name, light wall. The light wall oscillations may be due to the leakage of p-modes from below the photosphere.

MAGNETIC RECONNECTION BETWEEN SMALL-SCALE LOOPS OBSERVED WITH THE NEW VACUUM SOLAR TELESCOPE

Using the high tempo-spatial resolution H$\alpha$ images observed with the New Vacuum Solar Telescope, we report the solid observational evidence of magnetic reconnection between two sets of small-scale anti-parallel loops with an X-shaped topology. The reconnection process contains two steps: a slow step with the duration of more than several tens of minutes, and a rapid step lasting for only about three minutes. During the slow reconnection, two sets of anti-parallel loops reconnect gradually, and new loops are formed and stacked together. During the rapid reconnection, the anti-parallel loops approach each other quickly, and then the rapid reconnection takes place, resulting in the disappearance of former loops. In the meantime, new loops are formed and separate. The region between the approaching loops is brightened, and the thickness and length of this region are determined to be about 420 km and 1.4 Mm, respectively. During the rapid reconnection process, obvious brightenings at the reconnection site and apparent material ejections outward along reconnected loops are observed. These observed signatures are consistent with predictions by reconnection models. We suggest that the successive slow reconnection changes the conditions around the reconnection site and triggers instabilities, thus leading to the rapid approach of the anti-parallel loops and resulting in the rapid reconnection.

Reconnection in solar flares: Outstanding questions

Space observations of solar flares such as those from Yohkoh, SOHO, TRACE, and RHESSI have revealed a lot of observational evidence of magnetic reconnection in solar flares: cusp-shaped arcades, reconnection inflows, plasmoids, etc. Thus it has been established, at least phenomenologically, that magnetic reconnection does occur in solar flares. However, a number of fundamental questions and puzzles still remain in the physics of reconnection in solar flares. In this paper, we discuss the recent progresses and future prospects in the study of magnetic reconnection in solar flares from both theoretical and observational points of view.

Solar wind transport into magnetosphere caused by magnetic reconnection at high latitude magnetopause during northward IMF: Cluster-DSP conjunction observations

An event of Cluster-Double Star conjunction observations of magnetic reconnection at high latitude magnetopause nightside of both cusps and solar wind transport into magnetosphere caused by such reconnection process has been investigated. During northward IMF, Cluster/SC1 observed accelerated flows and ion heating associated with magnetic reconnection at high latitude magnetopause nightside of southern cusp. And Double Star observed cold dense solar wind plasma transported into dayside magnetosphere. The analysis on such conjunction observations shows that: (1) during northward IMF, magnetic reconnection occurs at high latitude nightside of southern cusp, accompanied by accelerated flows that are observed by Cluster/SC1; (2) the direction of the accelerated flows, with its sunward component Vx, dawnward component Vy, northward component Vz, is quite consistent with the theoretical anticipation under the condition of northward IMF with dawnward component By; (3) reconnection can heat plasma more in parallel direction than in perpendicular direction, to a level of about 4 keV; (4) with reconnection taking place at high latitude magnetopause nightside of the southern cusp, TC-1 observed cold and dense plasma transported into magnetosphere; (5) by reconnection at high latitude magnetopause nightside of both cusps, solar wind flux tube can be captured by magnetosphere and pulled into dayside magnetosphere. This event presents further observational evidence for magnetic reconnection at high latitude magnetopause nightside of both cusps as an important mechanism of solar wind transport into magnetosphere.

Particle acceleration in the magnetotail

Very prominent particle acceleration occurs during current disruption in the magnetotail. Although particle acceleration is frequently attributed to magnetic reconnection alone, particle heating and acceleration can equally well be associated with plasma instabilities which can be unrelated to magnetic reconnection. In this paper, the characteristics of particle acceleration for a well observed current disruption event is examined in detail. It is found that particle acceleration during this current disruption event is consistent with that expected from the development of the cross-field current instability. Furthermore, observational evidence of magnetic reconnection not causing particle acceleration during this current disruption event is also found.

Observational evidence of magnetic reconnection in solar X-ray jets

The solar X-ray jets are one of the most interesting findings of Soft X-Ray Telescope(SXT) aboard Yohkoh. They are transitory X-ray enhancements with an apparent collimated motion. In this paper, we present the observational evidence of magnetic reconnection of solar X-ray jets. From the morphological study of solar X-ray jets using SXT, we found the following properties of solar X-ray jets. 1) Most X-ray jets are associated with flares (microflares - flares) at their footpoints. 2) When the active regions at the footpoint of jets can be resolved well, it is found that morphology changes significantly during jets. 3) 27% of the jets show a gap (> 10 4 km) between the exact footpoint of the jet and the brightest part of the associated flare. Furthermore, as a result of the co-alignment between magnetograms and SXT images, we found that the jet-producing region are the mixed polarity region and the region of evolving magnetic flux (increasing or decreasing). Canfield et al. (1996) investigated some Hα surges which were associated with X-ray jets and found some new Hα phenomena (moving-blueshift feature, converging footpoint motion). They suggested that these phenomena are the results of magnetic reconnection. As the results, we propose that the solar X-ray jets are produced by energy input from the (micro)flares which are generated by magnetic reconnection.

Coronal X-Ray Jets Observed with the Yohkoh Soft X-Ray Telescope.

The soft X-ray telescope (SXT) aboard the Yohkoh spacecraft has revealed coronal X-ray jets associated with small flares in X-ray bright points (XBPs), emerging flux regions (EFRs), and active regions (ARs). These observations of X-ray jets are reviewed mainly from a morphological perspective. In particular, various observational evidence of magnetic reconnection in X-ray jets is discussed. It is suggested that magnetic reconnection between emerging magnetic flux and the coronal magnetic field is a key physical process for producing these jets.

The cancellation of magnetic flux on the quiet sun

The mutual loss of magnetic flux in closely spaced, opposite polarity magnetic fields is herein defined as “cancellation”. The combination of two cancelling components is referred to as a cancelling magnetic feature. In this paper, a classification scheme for cancelling magnetic features according to the origins of their two halves is proposed; the observed properties of flux cancellation are summarized. The cancellation appears to be the observational evidence of magnetic reconnection taking place in or above the photospheric layer.

Impulsive energy release in solar flares: A summary

Discoveries in solar physics made during the SMM-SMY-SMA period are highlighted, with special reference to impulsive energy release in solar flares. Major discoveries include observational evidence for magnetic reconnection and its theoretical interpretation, chromospheric evaporation to explain the simultaneous blue shift of X-ray lines and red shift of Hα, simultaneous production of high energy (Mev) electrons and protons, and their acceleration by Fermi shock acceleration upto 100 Mev energies, and evidence for a new acceleration process to explain the electron deficient very hard ion spectrum ( > 1000 Mev) in the extended emission phase of the large 1982 June 3 flare.

Observational Evidence for Magnetic Reconnection in Microwave Solar Bursts

In this paper, we first discuss a set of 6 cm observations made with the NRAO Very Large Array (VLA) (spatial resolution ~ 2″) that pertain to changes in the coronal magentic field configurations that took place before the onset of an impulsive burst observed on 14 May 1980. We also discuss a second set of 6 cm VLA observations (spatial resolution 18″ arc) where several interacting loops were involved in triggering the onset of an impulsive burst observed on June 24, 1980, 19:57:00 UT. Both sets of observations are examples of magnetic reconnection process being involved in accelerating microwave emitting electrons.

Recent advances in solar radio physics

We review high spatial resolution microwave observations of solar active regions, coronal loops and flares. Observations of preflare active regions are presented; in particular we discuss the interpretations of reversal of polarization at the flare site and the role of newly emerging flux in triggering the onset of flares. We discuss the spatial locations of microwave burst emitting regions; loops or arcades of loops appear to be the sites of flare energy release in microwave bursts. We provide direct observational evidence of magnetic reconnection as the primary cause of acceleration of electrons in microwave bursts.