arXiv subjects

Tatiana Podladchikova

Publications and source records attributed to Tatiana Podladchikova.

At least 19 recordsLinked to original sources

arXiv2026

The DIRECD coronal mass ejection direction catalog: three-dimensional propagation inferred from coronal dimmings

Coronal mass ejections (CMEs) are among the primary drivers of space weather disturbances at Earth, yet their early propagation in the low corona remains poorly constrained owing to occultation and projection effects inherent to coronagraph observations. Coronal dimmings offer an alternative diagnostic to infer CME propagation direction directly from the low corona. We present the DIRECD CME Direction Catalog, a unified dataset of three-dimensional CME propagation directions derived via the DIRECD (Dimming Inferred Estimation of CME Direction) method, which reconstructs CME cone geometry from SDO/AIA 211 Å coronal dimming observations. The catalog comprises 64 events spanning 2010-2026, combining 31 Solar Cycle 25 (2021-2026) events with 33 events from prior studies. For each event we report the 3D propagation direction, 2D inclination angles, angular width, and cone height. Statistical analysis reveals a systematic asymmetry in low-coronal CME propagation: meridional inclinations exhibit a systematic tendency toward latitude-dependent deflection, with poleward deflections more pronounced at higher source latitudes, while equatorial inclinations show no significant dependence on source longitude. This is consistent with low-coronal CME trajectories being governed primarily by local active-region magnetic topology, with the large-scale coronal field and heliospheric current sheet assuming a progressively dominant role at greater heliocentric distances. Incorporating DIRECD-derived propagation directions into CME arrival forecasts improves predictions of geomagnetic storm intensity, raising the correlation with observed storm strength from r = 0.58 to r = 0.70 when combined with CME speed. The DIRECD software, catalog, and all associated data products are publicly available to support space weather research.

astro-ph.SR↗

arXiv2026

Low-Cost Teleoperation Extension for Mobile Manipulators

Teleoperation of mobile bimanual manipulators requires simultaneous control of high-dimensional systems, often necessitating expensive specialized equipment. We present an open-source teleoperation framework that enables intuitive whole body control using readily available commodity hardware. Our system combines smartphone-based head tracking for camera control, leader arms for bilateral manipulation, and foot pedals for hands-free base navigation. Using a standard smartphone with IMU and display, we eliminate the need for costly VR helmets while maintaining immersive visual feedback. The modular architecture integrates seamlessly with the XLeRobot framework, but can be easily adapted to other types of mobile manipulators. We validate our approach through user studies that demonstrate improved task performance and reduced cognitive load compared to keyboard-based control.

cs.RO↗

arXiv2025

Coronal mass ejection arrival forecasting with the drag-based assimilation of satellite observations

Forecasting the arrival of coronal mass ejections (CMEs) is vital for protecting satellites, power systems, and human spaceflight. We present HELIOPANDA: Heliospheric Observer for Predicting CME Arrival via Nonlinear Drag Assimilation, a framework that integrates the Drag-Based Model (DBM) with spacecraft observations using iterative parameter estimation and Kalman filter assimilation. We introduce a method for estimating the solar wind speed $w$ and drag parameter $γ$, two key but usually unknown quantities controlling CME propagation, through direct solutions of the DBM equations. We tested the method on 4,480 synthetic CME profiles spanning CME speeds of $200-3500$ km/s, solar wind speeds of $250-800$ km/s, and drag parameters of $0.1-1.0\times10^{-7}$ km$^{-1}$. The results demonstrate that the framework provides accurate reconstructions of the DBM input parameters, providing a solid basis for in-situ and remote-sensing applications. By testing a single virtual spacecraft positioned at nine distances along the Sun-Earth line, HELIOPANDA achieved arrival-time errors as low as 0.6 hours for a 600 km/s CME and 1 hour for a 2500 km/s CME when the spacecraft was located 30 million km from the Sun. We developed a Kalman filter framework to assimilate noisy heliospheric data into the DBM, enabling recursive updates of CME kinematics and robust estimates of $w$ and $γ$, and yielding Earth and Mars arrival-time predictions within $1-2$ hours using 160 simulated hourly measurements. By combining DBM, parameter recovery, and data assimilation, HELIOPANDA provides a pathway to real-time, multi-point CME forecasts, suited to observations from Solar Orbiter, Parker Solar Probe, PUNCH, and planned L4/L5 missions.

astro-ph.SR↗

arXiv2025

Validating DIRECD: Statistical Evaluation of Coronal Mass Ejections Direction Estimates from Coronal Dimmings

Coronal mass ejections (CMEs) are among the most energetic phenomena in our solar system, with significant implications for space weather. Understanding their early dynamics remains challenging due to observational limitations in the low corona. We present a statistical evaluation of the DIRECD (Dimming InfeRred Estimation of CME Direction) method, which provides a novel approach to determining initial CME propagation directions using coronal dimmings. We analyze 33 coronal dimming events well observed by SDO/AIA and validate our DIRECD results with 3D reconstructions from the Graduated Cylindrical Shell (GCS) model. We find generally good agreement between the DIRECD-derived inclinations and the GCS model. In the meridional plane (north--south direction), the mean difference in inclinations is $0.3^\circ \pm 7.8^\circ$. In the equatorial plane (east--west direction), the mean difference is $-2.9^\circ \pm 18.9^\circ$. In 3D, the inclinations show a mean difference of $1.2^\circ \pm 10.4^\circ$. We further visually compare our method by projecting the DIRECD cones onto LASCO/C2 observations, and verify the model's ability to capture both the primary CME structure and associated secondary dimming regions. This work establishes DIRECD as a powerful, observationally grounded technique for determining the initial CME direction, offering new insights that complement existing reconstruction methods. The technique's unique capability to determine early CME direction in the low corona using coronal dimmings observed in EUV images makes it particularly valuable for improving space weather forecasting models.

astro-ph.SR↗

arXiv2025

Implementation and Analysis of Different Geomagnetic Field Models for Attitude Determination and Control System (ADCS) of a Satellite

An Attitude Determination and Control System is essential for orientation stability and performance of slew maneuvers on the satellite. This research focuses on comparing two different geomagnetic field models, Direct Dipole Model and International Geomagnetic Reference Field Model, for modeling of magnetometer and magnetorquers. Both these magnetic field models are compared and analyzed for two satellite attitude cases: orientation stability and unloading of reaction wheels. Magnetometer modeling is utilized to get sensor data for attitude determination and control to attain orientation stability. Whereas, the magnetorquer model aids in reaction wheel unloading, by performing the required actuation on the satellite, upon interaction with the Earth's magnetic field. The study offers a comprehensive lookout on the impact of geomagnetic field models on the overall ADCS performance, incorporating both attitude estimation and control via the sensor and actuator modeling. Apart from this, valuable insights are gained into selecting optimal models based on specific mission requirements and available computational resources. Finally, this comparison and analysis results in unique findings for an actual future satellite mission, that is to be launched soon.

eess.SY↗

arXiv2025

Coronal dimmings from active region 13664 during the May 2024 solar energetic events

Coronal dimmings are regions of transiently reduced brightness in extreme ultraviolet (EUV) and soft X-ray (SXR) emissions associated with coronal mass ejections (CMEs), providing key insights into CME initiation and early evolution. During May 2024, AR 13664 was among the most flare-productive regions in recent decades, generating 55 M-class and 12 X-class flares along with multiple Earth-directed CMEs. The rapid succession of these CMEs triggered the most intense geomagnetic storm in two decades. We study coronal dimmings from a single active region (AR 13664) and compare them with statistical dimming properties. We investigate how coronal dimming parameters - such as area, brightness, and magnetic flux - relate to key flare and CME properties. We systematically identified all flares above M1.0, all coronal dimmings and all CMEs (from the CDAW SOHO/LASCO catalogue) produced by AR 13664 during 2024 May 1 - 15, and studied the associations between the different phenomena and their characteristic parameters. We detect coronal dimmings in 22 events, with 16 occurring on-disc and six off-limb. Approximately 83% of X-class flares and 23% of M-class flares are associated with CMEs, with 13 out of 16 on-disc dimmings linked to CME activity. Our results support the strong interplay between coronal dimmings and flares, as we find increased correlations between flare and dimming parameters in this single-AR study compared to the general dimming population. Furthermore, we confirm that coronagraphic observations, unable to observe the lower corona, underestimate correlations between CME velocities and dimming parameters, as they fail to capture the early CME acceleration phase. This highlights the critical role of dimming observations in providing a more comprehensive understanding of CME dynamics.

astro-ph.SR↗

arXiv2025

Coronal dimmings and what they tell us about solar and stellar coronal mass ejections

Coronal dimmings associated with coronal mass ejections (CME) from the Sun have gained much attention since the late 1990s when they were first observed in high-cadence imagery of the SOHO/EIT and Yohkoh/SXT instruments. They appear as localized sudden decreases of the coronal emission at extreme ultraviolet (EUV) and soft X-ray (SXR) wavelengths, that evolve impulsively during the lift-off and early expansion phase of a CME. Coronal dimmings have been interpreted as "footprints" of the erupting flux rope and also as indicators of the coronal mass loss by CMEs. However, these are only some aspects of coronal dimmings and how they relate to the overall CME/flare process. The goal of this review is to summarize our current understanding and observational findings on coronal dimmings, how they relate to CME simulations, and to discuss how they can be used to provide us with a deeper insight and diagnostics of the triggering of CMEs, the magnetic connectivities and coronal reconfigurations due to the CME as well as the replenishment of the corona after an eruption. In addition, we go beyond a pure review by introducing a new, physics-driven categorization of coronal dimmings based on the magnetic flux systems involved in the eruption process. Finally, we discuss the recent progress in studying coronal dimmings on solar-like and late-type stars, and to use them as a diagnostics for stellar coronal mass ejections and their properties.

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arXiv2024

Three-part structure of solar coronal mass ejection observed in low coronal signatures of Solar Orbiter

This study examines the relationship between early solar coronal mass ejection (CME) propagation, the associated filament eruption, and coronal dimming in the rare event observed on March 28, 2022, which featured a three-part CME in the low corona of active region AR 12975, including a bright core/filament, dark cavity, and bright front edge. We employ 3D filament and CME shock reconstructions using data from SolO, STEREO-A, and SDO to track the filament's path, height, and kinematics. Our analysis across three viewpoints shows the outer front in SolO/EUI 304 Å aligns with shock structures in STEREO-A/EUVI 195 Å, showing a full 3D EUV wave dome, later matching the outer CME front in STEREO-A COR2. We introduce the method ATLAS-3D (Advanced Technique for single Line-of-sight Acquisition of Structures in 3D) and validate it against traditional approaches to reconstruct CME shock using SOLO data exclusively. Additionally, we estimate early CME propagation characteristics based on coronal dimming evolution with the DIRECD method. Results indicate that the filament height increased from 28 to 616 Mm (0.04 to 0.89 Rs) within 30 minutes (11:05 to 11:35 UT), reaching peak velocity of around 648 km/s and acceleration of around 1624 m/s$^2$. At 11:45 UT, the filament deflected by 12° to a height of 841 Mm (1.21 Rs), while the CME shock expanded from 383 to 837 Mm (0.55 to 1.2 Rs) over 10 minutes. Key parameters include a CME direction inclined by 6°, a 21° half-width, and a 1.12 Rs cone height at the dimming's impulsive phase end. This event demonstrates that expanding dimming correlates with early CME development, with the DIRECD method linking 2D dimming to 3D CME evolution. These insights underscore the value of multi-viewpoint observations and advanced reconstructions for improving space weather forecasting.

astro-ph.SR↗

arXiv2024

Estimating early coronal mass ejection propagation direction with DIRECD during the severe May 8 and follow-up June 8, 2024 events

On May 8, 2024, solar active region 13664 produced an X-class flare, several M-class flares, and multiple Earth-directed Coronal Mass Ejections (CMEs). The initial CME caused coronal dimmings, characterized by localized reductions in extreme-ultraviolet (EUV) emissions, indicating mass loss and expansion during the eruption. After one solar rotation, on June 8, 2024, the same region produced another M-class flare followed by coronal dimmings observed by the SDO and STEREO spacecraft. We analyzed early CME evolution and direction from coronal dimming expansion at the end of the impulsive phase using the DIRECD (Dimming Inferred Estimation of CME Direction) method. To validate the 3D CME cone, we compared CME properties from the low corona with white-light coronagraph data. The May 8 CME expanded radially, with a 7.7 deg inclination, 70 deg angular width, and 0.81 Rsun cone height, while the June 8 CME had a 15.7 deg inclination, 81 deg width, and 0.89 Rsun height. Our study shows that tracking low coronal signatures, like coronal dimming expansion, can estimate CME direction early, providing crucial lead time for space weather forecasts.

astro-ph.SR↗

arXiv2024

Coronal dimmings as indicators of early CME propagation direction

Coronal mass ejections (CMEs) are solar eruptions of plasma and magnetic fields that significantly impact Space Weather, causing disruptions in technological systems and potential damage to power grids when directed towards Earth. Traditional coronagraphs along the Sun-Earth line struggle to precisely track the early evolution of Earth-directed CMEs. Coronal dimmings, localized reductions in extreme-ultraviolet (EUV) and soft X-ray emissions, are key indicators of CMEs in the low corona, resulting from mass loss and expansion during the eruption. This study introduces a novel method, DIRECD (Dimming InfeRred Estimate of CME Direction), to estimate the early propagation direction of CMEs based on the expansion of coronal dimmings. The approach involves 3D simulations of CMEs using a geometric cone model, exploring parameters like width, height, source location, and deflection from the radial direction. The dominant direction of dimming evolution is then determined, and an inverse problem is solved to reconstruct an ensemble of CME cones at various heights, widths, and deflections. By comparing the CME orthogonal projections onto the solar sphere with the dimming geometry, the 3D CME direction is derived. Validated through case studies on October 1, 2011, and September 6, 2011, the DIRECD method reveals the early propagation directions of CMEs. The CME on October 1, 2011, predominantly expands towards the South-East, while the CME on September 6, 2011, inclines towards the North-West. These findings align with previous studies using multi-viewpoint coronagraphic observations. The study demonstrates the utility of coronal dimming information for early CME direction estimation, providing valuable data for space weather forecasting and mitigating potential adverse impacts on Earth before observation in coronographs' field-of-view.

astro-ph.SR↗

arXiv2024

Recovery of coronal dimmings

Coronal dimmings are regions of reduced emission in the lower corona, observed after coronal mass ejections (CMEs) and representing their footprints. In order to investigate the long-term evolution of coronal dimming and its recovery, we propose two approaches that focus on both the global and the local evolution of dimming regions: the fixed mask approach and the pixel boxes approach. We present four case studies (September 6, 2011; March 7, 2012; June 14, 2012; and March 8, 2019) in which a coronal dimming is associated with a flare/CME eruption. We identified the dimming region by image segmentation, then restricted the analysis to a specific portion of the dimming and tracked the time evolution of the dimming brightness and area. In addition, we studied the behavior of small subregions inside the dimming area, of about 3x3 pixels, to compare the recovery in different regions of the dimming. Three out of the four cases show a complete recovery 24 hours after the flare/CME eruption. The recovery of the brightness follows a two-step trend, with a steeper and quicker segment followed by a slower one. In addition, some parts of the dimming, which may be core dimmings, are still present at the end of the analysis time and do not recover within 3 days, whereas the peripheral regions (secondary dimmings) show a full recovery. We demonstrate that the primary mechanism for recovery identified in the observations is the expansion of coronal loops into the dimming region, which gradually increase their intensity. Our developed approaches enable the analysis of dimmings alongside these bright structures, revealing different timescales of recovery for core and secondary/twin dimming regions. Combined with magnetic field modeling, these methods lay the foundation for further systematic analysis of dimming recovery and enhance the knowledge gained from already-analyzed events.

astro-ph.SR↗

arXiv2024

Multipoint study of the rapid filament evolution during a confined C2 flare on 28 March 2022, leading to eruption

We studied the rapid filament evolution in AR 12975 during a confined C2 flare on 28 March 2022, which led to an eruptive M4 flare 1.5 h later. It is characterized by the breakup of the filament, the disappearance of its southern half, and the flow of the remaining plasma into a longer channel with a topology similar to an EUV hot channel during the flare. Our multipoint study takes advantage of Solar Orbiter's position at 0.33 AU and 83. 5° west of the Sun-Earth line. STIX and EUI onboard Solar Orbiter observed the event at the limb. AIA and HMI onboard SDO provided on-disk observations from which we derived DEM maps and NLFF magnetic field extrapolations. We find that both filament channels likely existed in close proximity before the flare. Based on field structures associated with AIA 1600 Å flare ribbons and kernels, we propose a loop-loop reconnection scenario between field lines that surround and pass beneath the shorter filament channel, and field lines following a portion of the longer channel. Reconnection occurs in an essentially vertical current sheet at a PIL below the breakup region, leading to the formation of the flare loop arcade and the EUV hot channel. The scenario is supported by concentrated currents and free magnetic energy built up by antiparallel flows along the PIL before the flare. The reconnection probably propagated to involve the original filament itself, leading to its breakup and reformation. The reconnection geometry provides a general mechanism for the formation of the long filament channel and realizes the concept of tether cutting, which was active throughout the filament's rise phase, lasting from at least 30 min before the C2 flare until the eruption. The C2 flare represents a period of fast reconnection during this otherwise more steady process, during which most of the original filament was reconnected and joined the longer channel.

astro-ph.SR↗

arXiv2024

A Universal Method for Solar Filament Detection from H-alpha Observations using Semi-supervised Deep Learning

Filaments are omnipresent features in the solar atmosphere. Their location, properties and time evolution can provide information about changes in solar activity and assist the operational space weather forecast. Therefore, filaments have to be identified in full disk images and their properties extracted from these images. Manual extraction is tedious and takes much time; extraction with morphological image processing tools produces a large number of false-positive detections. Automatic object detection, segmentation, and extraction in a reliable manner allows to process more data in a shorter time. The Chromospheric Telescope (ChroTel), Tenerife, Spain, the Global Oscillation Network Group (GONG), and the Kanzelhöhe Observatory (KSO), Austria, provide regular full-disk observations of the Sun in the core of the chromospheric H-alpha absorption line. We present a deep learning method that provides reliable extractions of filaments from H-alpha filtergrams. First, we train the object detection algorithm YOLOv5 with labeled filament data of ChroTel. We use the trained model to obtain bounding-boxes from the full GONG archive. In a second step, we apply a semi-supervised training approach, where we use the bounding boxes of filaments, to learn a pixel-wise classification of filaments with u-net. Here, we make use of the increased data set size to avoid overfitting of spurious artifacts from the generated training masks. Filaments are predicted with an accuracy of 92%. With the resulting filament segmentations, physical parameters such as the area or tilt angle can be easily determined and studied. This we demonstrate in one example, where we determine the rush-to-the pole for Solar Cycle 24 from the segmented GONG images. In a last step, we apply the filament detection to H-alpha observations from KSO which demonstrates the general applicability of our method to H-alpha filtergrams.

astro-ph.SR↗

arXiv2024

The McNish and Lincoln Solar Activity Predictions: The Method and its Performance

The McNish and Lincoln (ML) method, introduced in 1949, was one of the first attempts to produce mid-term forecasts of solar activity, up to 12 months ahead. However, it has been poorly described and evaluated in the past literature, in particular its actual operational implementation by NOAA. Here, we reconstruct the exact formulation of the method, as it was applied since the early 1970s, and we provide a full mathematical derivation of the prediction errors. For bench-marking the method, we also produce monthly predictions over the past 190 years, from 1833 (Cycle 8) to 2023 (Cycle 25), and develop statistics of the differences between the predictions and the observed 13-month smoothed sunspot number (SSN) time series, according to the phase in the solar cycle. Our analysis shows that the ML method is heavily constrained because it is primarily based on the mean of all past cycles, which imposes a fixed amplitude and length and suffers from a temporal smearing that grows towards the end of the solar cycle. We find that predictions are completely unreliable in the first 12 months of the cycle, and over the last two years preceding the ending minimum (around 130 months), and beyond this minimum. By contrast, in the course of the cycle (months 18 to 65), ML predictions prove to be reliable over a time range of up to 50 months (4.2 years), thus much longer than the 12-month conventional range used so far. However, we find that predictions then suffer from systematic under-(over-)estimates for cycles that have a higher (lower) amplitude than the base mean cycle. Overall, we conclude that although the ML method provides valid prediction errors, it suffers from strong limitations, with very little room for improvement, as it indifferently merges all past cycles into a single fixed statistics.

astro-ph.SR↗

arXiv2024

The Plasma $β$ in quiet Sun Regions: Multi-Instrument View

A joint campaign of several space-borne and ground-based observatories, such as the GREGOR solar telescope, the Extreme-ultraviolet Imaging Spectrometer (EIS), and the Interface Region Imaging Spectrograph (Hinode Observing Plan 381, 11-22 October 2019) was conducted to investigate the plasma $β$ in quiet sun regions. In this work, we focus on October 13, 17, and 19, 2019, to obtain the plasma $β$ at different heights through the solar atmosphere based on multi-height observational data. We obtained temperature, density and magnetic field estimates from the GREGOR High-resolution Fast Imager (HiFI), and Infrared Spectrograph (GRIS), IRIS, EIS and complementary data from SDO/AIA. Using observational data and models (e.g., FALC and PFSS), we determined the plasma $β$ in the photosphere, chromosphere, transition region and corona. The obtained plasma $β$ values lie inside the expected ranges through the solar atmosphere. However, at EIS and AIA coronal heights (from $1.03\ R_{\odot}$ to $1.20\ R_{\odot}$) plasma $β$ values appear in the limit defined by Gary (2001); such behavior was previously reported by Rodríguez Gómez et al. (2019). Additionally, we obtained the plasma $β$ in the solar photosphere at different optical depths from $\log\ τ=-1.0$ to $\log\ τ=-2.0$. These values decrease with optical depth. This work provides a complete picture of plasma $β$ in quiet sun regions through the solar atmosphere, which is a pre-requisite of a better understanding of the plasma dynamics at the base of the solar corona.

astro-ph.SR↗

arXiv2024

Instrument-To-Instrument translation: Instrumental advances drive restoration of solar observation series via deep learning

The constant improvement of astronomical instrumentation provides the foundation for scientific discoveries. In general, these improvements have only implications forward in time, while previous observations do not benefit from this trend. Here we provide a general deep learning method that translates between image domains of different instruments (Instrument-To-Instrument translation; ITI). We demonstrate that the available data sets can directly profit from the most recent instrumental improvements, by applying our method to five different applications of ground- and space-based solar observations. We obtain 1) solar full-disk observations with unprecedented spatial resolution, 2) a homogeneous data series of 24 years of space-based observations of the solar EUV corona and magnetic field, 3) real-time mitigation of atmospheric degradations in ground-based observations, 4) a uniform series of ground-based H$α$ observations starting from 1973, 5) magnetic field estimates from the solar far-side based on EUV imagery. The direct comparison to simultaneous high-quality observations shows that our method produces images that are perceptually similar and match the reference image distribution.

astro-ph.SR↗

arXiv2023

Advancing solar magnetic field extrapolations through multi-height magnetic field measurements

Non-linear force-free extrapolations are a common approach to estimate the 3D topology of coronal magnetic fields based on photospheric vector magnetograms. The force-free assumption is a valid approximation at coronal heights, but for the dense plasma conditions in the lower atmosphere, this assumption is not satisfied. In this study, we utilize multi-height magnetic field measurements in combination with physics-informed neural networks to advance solar magnetic field extrapolations. We include a flexible height-mapping, which allows us to account for the different formation heights of the observed magnetic field measurements. The comparison to analytical and simulated magnetic fields demonstrates that including chromospheric magnetic field measurements leads to a significant improvement of our magnetic field extrapolations. We also apply our method to chromospheric line-of-sight magnetograms, from the Vector Spectromagnetograph (VSM) on the Synoptic Optical Long-term Investigations of the Sun (SOLIS) observatory, in combination with photospheric vector magnetograms, from the Helioseismic Magnetic Imager (HMI) onboard the Solar Dynamic Observatory (SDO). The comparison to observations in extreme ultraviolet wavelengths shows that the additional chromospheric information leads to a better agreement with the observed coronal structures. In addition, our method intrinsically provides an estimate of the corrugation of the observed magnetograms. With this new approach, we make efficient use of multi-height magnetic field measurements and advance the realism of coronal magnetic field simulations.

astro-ph.SR↗

arXiv2023

Multi-point study of the energy release and transport in the 28 March 2022, M4-flare using STIX, EUI, and AIA during the first Solar Orbiter nominal mission perihelion

We present a case study of an M4-class flare on 28 March 2022, near Solar Orbiter's first science perihelion (0.33 AU). Solar Orbiter was 83.5° west of the Sun-Earth line, making the event appear near the eastern limb, while Earth-orbiting spacecraft observed it near the disk center. The timing and location of the STIX X-ray sources were related to the plasma evolution observed in the EUV by the Extreme Ultraviolet Imager (EUI) on Solar Orbiter and the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory, and to the chromospheric response observed in 1600 Å by AIA. We performed differential emission measure (DEM) analysis to further characterize the flaring plasma at different subvolumes. The pre-flare magnetic field configuration was analyzed using a nonlinear force-free (NLFF) extrapolation. In addition to the two classical hard X-ray (HXR) footpoints at the ends of the flaring loops, later in the event we observe a nonthermal HXR source at one of the anchor points of the erupting filament. The evolution of the AIA 1600~Å footpoints indicates that this change in footpoint location represents a discontinuity in an otherwise continuous westward motion of the footpoints throughout the flare. The NLFF extrapolation suggests that strongly sheared field lines close to, or possibly even part of, the erupting filament reconnected with a weakly sheared arcade during the first HXR peak. The remainder of these field lines reconnected later in the event, producing the HXR peak at the southern filament footpoint. Our results show that the reconnection between field lines with very different shear in the early phase of the flare plays a crucial role in understanding the motion of the HXR footpoint during later parts of the flare. This generalizes simpler models, such as whipping reconnection, which only consider reconnection propagating along uniformly sheared arcades.

astro-ph.SR↗