Active Region NOAA Research Articles

The Formation Process of the First Halo Coronal Mass Ejection in Solar Cycle 25: Magnetic Cancellation, Bidirectional Jet, and Hot Channel

Abstract To better understand the trigger mechanism of a coronal mass ejection (CME), we present the evolution of a CME source region (active region NOAA 12790) and the formation of a hot channel before the occurrence of the first halo CME in solar cycle 25. Through analyzing the evolution of Solar Dynamics Observatory/Helioseismic and Magnetic Imager line-of-sight magnetograms, it is found that continuous magnetic cancellation occurs at the polarity inversion line (PIL) in this active region. With ongoing magnetic cancellation, several bidirectional jets and unidirectional jets occur along the large-scale arched magnetic loops. A hot channel forms during the first bidirectional jet. After the occurrence of the fourth bidirectional jet, the hot channel immediately erupts and produces a C-class flare, a cusp structure, and a halo CME. It is worth pointing out that the cusp structure only appears in the 131 Å and 94 Å observations (temperature about 10 MK). The obvious contraction of the newly formed loops is observed at the top of the cusp structure. The observations reveal a clear physics process: magnetic cancellation of a bipolar magnetic field at the PIL results in the occurrence of the bidirectional/unidirectional jets and the formation of the hot channel. The axial magnetic flux feeding for the hot channel through the continued magnetic cancellation leads to the hot channel eruption, which results in the formation of the hot cusp structure and the occurrence of the C-class flare and the halo CME.

Penumbral decay observed in active region NOAA 12585

Context. The physical conditions leading the sunspot penumbra decay are poorly understood so far. Aims. We investigate the photospheric magnetic and velocity properties of a sunspot penumbra during the decay phase to advance the current knowledge of the conditions leading to this process. Methods. A penumbral decay was observed with the CRISP instrument at the Swedish 1 m Solar Telescope on 2016 September 4 and 5 in the active region NOAA 12585. During these days, full-Stokes spectropolarimetric scans along the Fe I 630 nm line pair were acquired over more than one hour. We inverted these observations with the VFISV code to obtain the evolution of the magnetic and velocity properties. We complement the study with data from instruments on board the Solar Dynamics Observatory and Hinode space missions. Results. The studied penumbra disappears progressively in time and space. The magnetic flux evolution seems to be linked to the presence of moving magnetic features (MMFs). Decreasing Stokes V signals are observed. Evershed flows and horizontal fields were detected even after the disappearance of the penumbral sector. Conclusions. The analyzed penumbral decay seems to result from the interaction between opposite polarity fields in type III MMFs and penumbra, while the presence of overlying canopies regulates the evolution in the different penumbral sectors.

Extreme-ultraviolet Late Phase in Homologous Solar Flares from a Complex Active Region

Abstract Recent observations in extreme-ultraviolet (EUV) wavelengths reveal a new late phase in some solar flares, which is seen as a second peak in warm coronal emissions (∼3 MK) several tens of minutes to a few hours after the soft X-ray peak. The origin of the EUV late phase (ELP) is explained by either a long-lasting cooling process in the long ELP loops or a delayed energy ejection into the ELP loops well after the main flare heating. Using the observations with the Solar Dynamics Observatory, we investigate the production of the ELP in six homologous flares (F1–F6) originating from a complex active region (AR), NOAA Active Region 11283, with an emphasis on the emission characteristics of the flares. It is found that the main production mechanism of the ELP changes from additional heating in flare F1 to long-lasting cooling in flares F3–F6, with both mechanisms playing a role in flare F2. The transition is evidenced by an abrupt decrease of the time lag of the ELP peak, and the long-lasting cooling process in the majority of the flares is validated by a positive correlation between the flare ribbon fluence and the ELP peak intensity. We attribute the change in ELP production mechanism to an enhancement of the envelope magnetic field above the AR, which facilitates a more prompt and energetic heating of the ELP loops. In addition, the last and the only confined flare F6 exhibits an extremely large ELP. The different emission pattern revealed in this flare may reflect a different energy partitioning inside the ELP loops, which is due to a different magnetic reconnection process.

A Transient Coronal Sigmoid in Active Region NOAA 11909: Build-up Phase, M-class Eruptive Flare, and Associated Fast Coronal Mass Ejection

In this article, we investigate the formation and disruption of a coronal sigmoid from the active region (AR) NOAA 11909 on 07 December 2013, by analyzing multi-wavelength and multi-instrument observations. Our analysis suggests that the formation of the sigmoid initiated ≈ 1 hour before its eruption through a coupling between two twisted coronal loop systems. This sigmoid can be well regarded as of ‘transient’ class due to its short lifetime as the eruptive activities started just after ≈ 20 min of its formation. A comparison between coronal and photospheric images suggests that the coronal sigmoid was formed over a simple \(\beta \)-type AR which also possessed dispersed magnetic field structure in the photosphere. The line-of-sight photospheric magnetograms also reveal small-scale flux cancellation events near the polarity inversion line, and overall flux cancellation during the extended pre-eruption phase which suggest the role of tether-cutting reconnection toward the build-up of the flux rope. The disruption of the sigmoid proceeded with a two-ribbon eruptive M1.2 flare (SOL2013-12-07T07:29). In radio frequencies, we observe type III and type II bursts in meter wavelengths during the impulsive phase of the flare. The successful eruption of the flux rope leads to a fast coronal mass ejection (with a linear speed of ≈ 1085 km s−1) in SOHO/LASCO field-of-view. During the evolution of the flare, we clearly observe typical “sigmoid-to-arcade” transformation. Prior to the onset of the impulsive phase of the flare, flux rope undergoes a slow rise (≈ 15 km s−1) which subsequently transitions into a fast eruption (≈ 110 km s−1). The two-phase evolution of the flux rope shows temporal associations with the soft X-ray precursor and impulsive phase emissions of the M-class flare, respectively, thus pointing toward a feedback relationship between magnetic reconnection and early CME dynamics.

Eruptivity in Solar Flares: The Challenges of Magnetic Flux Ropes

Abstract Two new schemes for identifying field lines involved in eruptions, the r-scheme and q-scheme, are proposed to analyze the eruptive and confined nature of solar flares, as extensions to the original r m scheme proposed in Lin et al. Motivated by three solar flares originating from NOAA Active Region 12192 that are misclassified by r m , we introduce refinements to the r-scheme employing the “magnetic twist flux” to approximate the force balance acting on a magnetic flux rope (MFR); in the q-scheme, the reconnected field is represented by those field lines that anchor in the flare ribbons. Based on data obtained by the Solar Dynamics Observatory/Helioseismic and Magnetic Imager, the coronal magnetic field for 51 flares larger than M5.0 class, from 29 distinct active regions, is constructed using a nonlinear force-free field extrapolation model. Statistical analysis based on linear discriminant function analysis is then performed, revealing that despite both schemes providing moderately successful classifications for the 51 flares, the coronal mass ejection-eruptivity classification for the three target events can only be improved with the q-scheme. We find that the highly twisted field lines and the flare-ribbon field lines have equal average force-free constant α, but all of the flare-ribbon-related field lines are shorter than 150 Mm in length. The findings lead us to conclude that it is challenging to distinguish the MFR from the ambient magnetic field using any quantity based on common magnetic nonpotentiality measures.

Two-Stage Evolution of an Extended C-Class Eruptive Flaring Activity from Sigmoid Active Region NOAA 12734: SDO and Udaipur-CALLISTO Observations

In this article, we present a multi-wavelength investigation of a C-class flaring activity that occurred in the active region NOAA 12734 on 8 March 2019. The investigation utilizes data from the Atmospheric Imaging Assembly (AIA) and the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) and the Udaipur-CALLISTO solar radio spectrograph of the Physical Research Laboratory. This low intensity C1.3 event is characterized by typical features of a long-duration event (LDE), viz. extended flare arcade, large-scale two-ribbon structures and twin coronal dimmings. The eruptive event occurred in a coronal sigmoid and displayed two distinct stages of energy release, manifested in terms of temporal and spatial evolution. The formation of twin-dimming regions are consistent with the eruption of a large flux rope with footpoints lying in the western and eastern edges of the coronal sigmoid. The metric radio observations obtained from Udaipur-CALLISTO reveals a broad-band ( $\approx50\,\text{--}\,180~\text{MHz}$ ), stationary plasma emission for $\approx7~\text{min}$ during the second stage of the flaring activity that resemble a type IV radio burst. A type III decametre-hectometre radio bursts with starting frequency of $\approx2.5~\text{MHz}$ precedes the stationary type IV burst observed by Udaipur-CALLISTO by $\approx5~\text{min}$ . The synthesis of multi-wavelength observations and non-linear force-free field (NLFFF) coronal modeling together with magnetic decay index analysis suggest that the sigmoid flux rope underwent a zipping-like uprooting from its western to eastern footpoints in response to the overlying asymmetric magnetic field confinement. The asymmetrical eruption of the flux rope also accounts for the observed large-scale structures viz. apparent eastward shift of flare ribbons and post-flare loops along the polarity inversion line (PIL), and provides evidence for lateral progression of magnetic reconnection site as the eruption proceeds.

Temporal and Spatial Association Between a Solar Flare, CME, and Radio Burst on 19 November 2013

We present multi-wavelength and multi-instrument observations and analysis of a major X 1.0 class flare, radio burst, halo coronal mass ejection (CME), and loop eruption from the solar active region NOAA 11893 on 19 November 2013 (SOL2013-11-19T10:26). The aim of this work is twofold: The first aim to study the evolution of the loop eruption and the second is to find the link between this eruption and radio emissions. Initial signatures of eruption from the solar source region are confirmed using observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory in the hot channel at 94 A wavelength. These observations confirm that the source of the CME was associated with a magnetic-loop eruption, which was visible before the flare initiation. The photospheric magnetic configuration displayed a complex network of $\upbeta \updelta $ sunspots. After the eruption, a CME was observed by the Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph with linear speed and acceleration of $740~\text{km}\,\text{s}^{-1}$ and $-2~\text{m}\,\text{s}^{-2}$ , respectively. Dynamic radio-spectrum observation from the Learmonth Observatory in the metric frequency range shows Type-III and Type-II radio emissions that reveal the field-line opening and coronal-shock formation closely associated with the CME. From the metric Type-II radio observation and assuming Newkirk’s density model, we estimate the shock formation height range of $1.14\,\text{--}\,1.54~\text{R}_{\odot }$ with the corresponding shock speed ( $\approx650~\text{km}\,\text{s}^{-1}$ ). With the heliographic observations from the Nancay heliograph at different frequencies we could disentangle Type-II bursts from Type-III bursts. Likely, the Type-III burst would correspond to the loop eruption while the Type-II comes from the northern flank of the CME.

Magnetic Helicity Flux across Solar Active Region Photospheres. II. Association of Hemispheric Sign Preference with Flaring Activity during Solar Cycle 24

Abstract In our earlier study (Paper I) of this series, we examined the hemispheric sign preference (HSP) of magnetic helicity flux dH/dt across photospheric surfaces of 4802 samples of 1105 unique active regions (ARs) observed during solar cycle 24. Here, we investigate any association of the HSP, expressed as a degree of compliance, with flaring activity, analyzing the same set of dH/dt estimates as used in Paper I. The AR samples under investigation are assigned to heliographic regions (HRs) defined in the Carrington longitude–latitude plane with a grid spacing of 45° in longitude and 15° in latitude. For AR samples in each of the defined HRs, we calculate the degree of HSP compliance and the average soft X-ray flare index. The strongest flaring activity is found to be in one distinctive HR with an extremely low-HSP compliance of 41% as compared to the mean and standard deviation of 62% and 7%, respectively, over all HRs. This sole HR shows an anti-HSP (i.e., <50%) and includes the highly flare-productive AR NOAA 12673, however this AR is not uniquely responsible for the HR’s low HSP. We also find that all HRs with the highest flaring activity are located in the southern hemisphere, and they tend to have lower degrees of HSP compliance. These findings point to the presence of localized regions of the convection zone with enhanced turbulence, imparting a greater magnetic complexity and a higher flaring rate to some rising magnetic flux tubes.

Nonequilibrium Flux Rope Formation by Confined Flares Preceding a Solar Coronal Mass Ejection

Abstract We present evidence that a magnetic flux rope was formed before a coronal mass ejection (CME) and its associated long-duration flare during a pair of preceding confined eruptions and associated impulsive flares in a compound event in NOAA Active Region 12371. Extreme-ultraviolet images and the extrapolated nonlinear force-free field show that the first two (impulsive) flares, SOL2015-06-21T01:42, result from the confined eruption of highly sheared low-lying flux, presumably a seed flux rope. The eruption spawns a vertical current sheet, where magnetic reconnection creates flare ribbons and loops, a nonthermal microwave source, and a sigmoidal hot channel that can only be interpreted as a magnetic flux rope. Until the subsequent long-duration flare, SOL2015-06-21T02:36, the sigmoid’s elbows expand, while its center remains stationary, suggesting nonequilibrium but not yet instability. The “flare reconnection” during the confined eruptions acts like “tether-cutting reconnection” whose flux feeding of the rope leads to instability. The subsequent full eruption is seen as an accelerated rise of the entire hot channel, seamlessly evolving into the fast halo CME. Both the confined and ejective eruptions are consistent with the onset of the torus instability in the dipped decay index profile that results from the region’s two-scale magnetic structure. We suggest that the formation or enhancement of a nonequilibrium but stable flux rope by confined eruptions is a generic process occurring prior to many CMEs.

Comparison of physical conditions in two phases of the solar flare of July 19, 2000 of M6.4/3N class

We study the solar flare of July 19, 2000 of M6.4/3N class, which occurred in the active region NOAA 9087. Echelle Zeeman spectrograms of this flare were obtained with the horizontal solar telescope of the Astronomical Observatory of Taras Shevchenko National University of Kyiv. Physical conditions were compared for two times corresponding to the pre-peak and peak phases of the flare in area of a small sunspot. It was found that the effective magnetic field $B$ eff by Fe I 6301.5 and Fe I 6302.5 lines was almost the same for both times and both spectral lines. However, $B$ eff in peak phase measured by the splitting of the emission peaks of Fe II and H $\upbeta $ lines turned out to be 300–500 G stronger than those by the above-mentioned Fe I lines, whereas by D3 He I line it was found to be close to zero. This may indicate a local magnetic field increase in height range from temperature minimum region to the lower chromosphere. A semi-empirical model of the photospheric layers of the flare, constructed on a base of observations of Fe I 5123.7 and Fe I 5434.5 lines by solving the inverse problem for non-equilibrium radiative transfer using Tikhonov stabilizers, shows the moderate increasing of temperature (∼300 K) in altitude range 250–500 km. The radial velocities were decreased during peak phase. The micro-turbulent velocity was increased in the photosphere layers before the flare peak, while during the peak phase it was significantly decreased. The obtained results indicate that in the pre-peak phase the altitude perturbations in the photosphere were larger than in the peak phase.

Multi-wavelength analysis of CME-driven shock and Type II solar radio burst band-splitting

It is now well established that Coronal Mass Ejections (CMEs) may produce shocks in near Sun and interplanetary medium. A Type-II radio burst is characterized by shock and associated emission with very slow frequency drift rate (∼0.1 MHz/sec). A CME driven shock and their velocity, acceleration/deceleration signature can be observed by a Type-II solar radio burst which drifts with the shock speed and is split in bands of plasma radio emission. These emissions can be seen in radio spectrographs as split bands both in fundamental and harmonic frequencies close to a ratio of 1:2. In this paper, we present an analysis of a CME associated with a band splitting Type-II radio burst observed using multi-instruments in multi-wavelengths. We observed the CME event that occurred in 02 May 2013 (05:24 UT) and is associated with an M1.1 class solar flare from the active region NOAA 11731 located at N10W23 on the solar disk. We use the widely accepted Newkirk coronal density model to estimate the height in the solar atmosphere to compare our results. We conclude that the speed of CME is high enough to produce a Type-II solar radio burst. The analysis of this paper also involved an estimation of the coronal ambient magnetic field and its comparison with the empirical active region magnetic field model (Dulk and McLean in Sol. Phys. 57:279, 1978). This shows the good results. Observations provide sufficient evidence that the unusual patch signature in Type-II solar radio burst is due to the CME–CME interaction.

Development of an M6.4 Circular Solar Flare According to the Observations in the Нα Line

The development of the 3N/M6.4 flare on July 19, 2000, in the active region NOAA 9087 was studied based on the analysis of its images in the Нα line. Нα filtergrams obtained at the Meudon Observatory were used. The flare-active region NOAA 9087 had a complex multipolar magnetic field structure. The flare of 3N/M6.4 class began with the appearance of two bright kernels near a large spot. A few minutes later, flare kernels appeared in the central part of the active region, where a coronal source of hard X-ray radiation was identified. The flare lasted 2.5 h. Its energy was released sequentially in different places of the active region. The flare kernels were located along the polarity inversion line at the boundaries of the chromospheric cells. The flare ribbons had a circular shape. An assumption is made about the magnetic topology of the fan-spine type containing a null point. In this case, flare ribbons are the intersections of the fan quasi-separatrix layer with the lower atmosphere. The successive appearance of flare kernels may indicate a slipping magnetic reconnection in the flare. The Нα images in the main phase of the flare show reconnecting loops in the eastern part of the active region that are clearly visible in the ultraviolet wavelength range.

A three-dimensional velocity of an erupting prominence prior to a coronal mass ejection

Abstract We present a detailed three-dimensional (3D) view of a prominence eruption, coronal loop expansion, and coronal mass ejections (CMEs) associated with an M4.4 flare that occurred on 2011 March 8 in the active region NOAA 11165. Full-disk Hα images of the flare and filament ejection were successfully obtained by the Flare Monitoring Telescope (FMT) following its relocation to Ica University, Peru. Multiwavelength observation around the Hα line enabled us to derive the 3D velocity field of the Hα prominence eruption. Features in extreme ultraviolet were also obtained by the Atmospheric Imager Assembly onboard the Solar Dynamic Observatory and the Extreme Ultraviolet Imager on board the Solar Terrestrial Relations Observatory - Ahead satellite. We found that, following collision of the erupted filament with the coronal magnetic field, some coronal loops began to expand, leading to the growth of a clear CME. We also discuss the succeeding activities of CME driven by multiple interactions between the expanding loops and the surrounding coronal magnetic field.

Magnetohydrodynamics model of an X-class flare in NOAA active region 12017 initiated with non-force-free extrapolation

We present a three-dimensional magnetohydrodynamic simulation of the NOAA active region 12017 to explore the onset of an X-class flare on 2014 March 29 at 17:48 UT. The simulation is initiated with a magnetic field constructed by non-force-free-field extrapolation of the photospheric magnetic field. Importantly, the initial field contains a three-dimensional magnetic null, a pair of magnetic flux ropes, and a set of sheared arcades overlying the flux ropes at the flare location. A set of magnetic field lines are also identified which connect the flaring location to a distant region affected by the flare. The simulated evolution documents the magnetic reconnections at the null, which can potentially explain the observed chromospheric brightenings during the flare. The sheared arcades also appear to rise and participate in reconnections at the null. Notably, under the favorable initial Lorentz force, the flux ropes lose their twist due to reconnection. The terminal geometry of the ropes and the arcades are similar to the observed post-flare loops. Interestingly, the connecting field lines appear to take part in reconnections at the null, which may lead to the brightenings at the distant region. Further, the free energy released during the evolution which turns out to be ≈6.8×1031 ergs matches well with the observation.

Diagnosing a Solar Flaring Core with Bidirectional Quasi-periodic Fast Propagating Magnetoacoustic Waves

Abstract Quasi-periodic fast propagating (QFP) waves are often excited by solar flares, and could be trapped in the coronal structure with low Alfvén speed, so they could be used as a tool for diagnosing both the flaring core and magnetic waveguide. As the periodicity of a QFP wave could originate from a periodic source or be dispersively waveguided, it is a key parameter for diagnosing the flaring core and waveguide. In this paper, we study two QFP waves excited by a Geostationary Operational Environmental Satellite-class C1.3 solar flare occurring at active region NOAA 12734 on 2019 March 8. Two QFP waves were guided by two oppositely oriented coronal funnels. The periods of two QFP waves were identical and were roughly equal to the period of the oscillatory signal in the X-ray and 17 GHz radio emission released by the flaring core. It is very likely that the two QFP waves could be periodically excited by the flaring core. Many features of this QFP wave event are consistent with the magnetic tuning fork model. We also investigated the seismological application with QFP waves, and found that the magnetic field inferred with magnetohydrodynamic seismology was consistent with that obtained in the magnetic extrapolation model. Our study suggests that the QFP wave is a good tool for diagnosing both the flaring core and the magnetic waveguide.

Evolutionary stages and triggering process of a complex eruptive flare with circular and parallel ribbons

ABSTRACT We report multiwavelength study of a complex M-class solar eruptive flare that consists of three different sets of flare ribbons, viz. circular, parallel, and remote ribbons. Magnetic field modelling of source active region NOAA 12242 exhibits the presence of 3D null-point magnetic topology that encompasses an inner bipolar region. The event initiates with the faint signatures of the circular ribbon along with remote brightening right from the pre-flare phase that points toward the ongoing slow yet persistent null-point reconnection. We first detected flux cancellation and an associated brightening, which are likely signatures of tether-cutting reconnection that builds the flux rope near the polarity inversion line (PIL) of the inner bipolar region. In the next stage, with the onset of M8.7 flare, there is a substantial enhancement in the brightening of circular ribbon, which essentially suggests an increase in the rate of ongoing null-point reconnection. Finally, the eruption of underlying flux rope triggers ‘standard flare reconnection’ beneath it producing an abrupt rise in the intensity of the parallel ribbons as well as enhancing the rate of null-point reconnection by external forcing. We show that within the the fan dome, the region with magnetic decay index n > 1.5 borders the null-point QSL. Our analysis suggests that both the torus instability and the breakout model have played role toward the triggering mechanism for the eruptive flare. This event is a nice example of the dynamical evolution of a flux rope initially confined in a null-point topology that subsequently activates and erupts with the progression of the circular-cum-parallel ribbon flare.

Spectral Study of the Active Region with the Ellerman Bomb and Hα Surges. Chromosphere. Ellerman Bomb

The results from the analysis of spectral observations in the Hα line of the active region (AR) NOAA 11024, in which the Ellerman bomb (EB) and various chromospheric surges developed, are presented. Spectral data with high spatial and temporal resolution were obtained using the THEMIS French–Italian solar telescope (Tenerife, Spain) on July 4, 2009. The observation time was 20 min. On the day of the observations, the AR was at the stage of a sharp increase in activity. The Hα line profiles obtained for different periods of the Ellerman bomb development were very diverse, mainly consisted of several components, and were asymmetrical with excess emission in the short-wavelength wing. The maximum increase in the intensity of the emission component, compared with the profile for the AR segment without active formations, in the short-wavelength wing by 73% and in the long-wavelength wing by 35% occurred at a distance of ±0.16 nm from the core of the Hα line. The temporal variations of intensity in the wings of the Hα line indicate that there was a gradual energy release for the first 8 min of the Ellerman bomb development and then there was a pulse energy release for 6 min. The EB brightness increase period consisted of five peaks with an interval of approximately 1 min. The obtained temporal changes in the line-of-sight velocity (Vlos) of the chromospheric matter over the EB development region at the level of the Hα line core formation indicate that the velocity distribution in this region was mainly due to the development of chromospheric surges. In the segment without active formations, values of Vlos experienced small fluctuations within ±2 km/s. Two periods of increase in Vlos are distinguished. They consisted of several individual peaks: in the first half of the observations, the chromospheric matter mainly moved upward, while it mainly moved downward in the second half of the observations. Above the EB development region, different kinds of Hα-surges were observed. The maximum upward velocity in the return surges reached –12 to –16 km/s and the chromospheric matter descended along the same trajectories of magnetic loops with two times higher velocity, up to 22–30 km/s. In the loop surge, the maximum upward velocity on one side of the loop was –7 km/s and the downward velocity on the other side reached 18 km/s. One of the surges showed signs of plasma vortex motions, as evidenced by the inclined dark streaks in the spectra. Features of intensity variation in the wings of the Hα line and in the line-of-sight velocity of the chromospheric matter indicate that the Ellerman bomb and the accompanying Hα-surges, which appeared and developed in the AR under study, resulted from the magnetic reconnection caused by the emergence of the new serpentine magnetic flux and its interaction with the pre-existing magnetic field or between the magnetic loops of the flux itself.

ДОСЛІДЖЕННЯ ЗВ'ЯЗКУ МІЖ БОМБОЮ ЕЛЛЕРМАНА І Hα-СЬОРЖАМИ

Based on the analysis of spectral observations in the H α line of a site of the active region NOAA 11024, where the Ellerman bomb appeared and developed and during our observations various types of chromospheric matter ejections were formed, a study of the connection between these small-scale elements of solar activity has been carried out. Spectral data with high spatial and temporal resolution were obtained with the French–Italian 90-cm vacuum telescope THEMIS (Tenerife, Spain) on July 4, 2009. The observation time was 20 minutes. The AR site under investigation was in the region of a new magnetic flux emerging at this time. A site with high activity was select – it was pore on it, the Ellerman bomb (EB) was developing and many chromospheric ejections (surge) arose. The features of the formation and development of surges that appeared near the pore, which was at a distance of 7.2 Mm from the Ellerman bomb, were studied. Changes in the line-of-sight velocity (Vlos) and the direction of chromospheric matter motion in Hα-surges are analyzed. During our observations, the maximum plasma velocity upward reached – 95 km/s, and downward – 80 km/s. In the upper part of the magnetic loops, the Vlos of the plasma varied between – 20 km/s and 15 km/s. The velocity values in the area without active formations did not exceed ± 2 km/s. The distribution of velocities within Hα-surges showed that they mainly had a fine structure – they consisted of several jets. In most cases, upward and downward plasma flows occurred simultaneously with an increase in the EB brightness. Our study showed that during a sharp increase in the brightness of the EB, the chromospheric mater velocities in the surges increased, the direction of its movement changed, new surges appeared, which indicates a connection of the Hα-surges that developed near the pore with the Ellerman bomb, as well indicates that all these processes were the result of magnetic reconnections caused by the emergence of a new serpentine magnetic flux and its interaction with the pre-existing magnetic field.

Structure and Evolution of an Inter–Active Region Large-scale Magnetic Flux Rope

Abstract Magnetic flux rope (MFR) has been recognized as the key magnetic configuration of solar eruptions. While pre-eruption MFRs within the core of solar active regions (ARs) have been widely studied, those existing between two ARs, i.e., the intermediate ones in weak-field regions, were rarely studied. There are also major eruptions that occurred in such intermediate regions and study of the MFR there will help us understand the physics mechanism underlying the eruptions. Here, with a nonlinear force-free field reconstruction of solar coronal magnetic fields, we tracked the five-day evolution covering the full life of a large-scale inter-AR MFR forming between ARs NOAA 11943 and 11944, which is closely cospatial with a long sigmoidal filament channel and an eruptive X1.2 flare occurring on 2014 January 7. Through topological analysis of the reconstructed 3D magnetic field, it is found that the MFR begins to form early on 2014 January 6; then with its magnetic twist degree continuously increasing for over 30 hr, it becomes highly twisted with field lines winding numbers approaching six turns, which might be the highest twisting degree in extrapolated MFRs that have been reported in the literature. The formation and strength of the MFR are attributed to a continuous sunspot rotation of AR 11944 and flux cancellation between the two ARs. The MFR and its associated filaments exhibit no significant change across the flare time, indicating it is not responsible for the flare eruption. After the flare, the MFR slowly disappears, possibly due to the disturbance by the eruption.

Solar Type U Burst Associated with a High Coronal Loop

An inverted U burst with equally developed ascending and descending branches observed by Giant Ukrainian Radio Telescope (GURT) on 18 April 2017 in meter wavelengths band is discussed. This U burst was attributed to the high coronal loop above the limb active region NOAA 12651. Under the assumption that, associated with the burst, the coronal loop confines isothermal plasma stratified according to a Boltzmann density relation, the geometrical and physical parameters of the loop were estimated. According to our model coronal loops may contain plasma which is up to 20 times denser than the surrounding coronal plasma. In general the proposed model gives the relation between the plasma temperature and the height of the loop in such a way that under the given parameters of the associated U burst, higher loops contain cooler plasma and vice versa. An alternative method of coronal loop height determination was suggested. Assuming that the observed U burst and the preceding type III burst were generated by the same exciter we define the height of the loop from the delay of the former with respect to the latter at certain frequency. We show that defining of coronal loops heights by another independent method, e.g. interferometric or tied-array imaging may solve the uncertainty of the inside-the-loop plasma temperature determination.