arXiv subjects

Weiqun Gan

Publications and source records attributed to Weiqun Gan.

At least 19 recordsLinked to original sources

arXiv2026

Three-dimensional properties of a coronal shock and the longitudinal distribution of its related solar energetic particles

This study aims to investigate the relationship between the spatial-temporal evolution of shock properties and the longitudinal dependence of SEP intensities and spectra. The shock parameters, including the normal speed, oblique angles, compression ratio, and Alfven Mach number, were derived by combining a steady-state solar-wind simulation with the three-dimensional (3D) reconstruction of the shock surface based on multi-view observations. We compared the local shock parameters at the magnetic connecting points with in situ proton intensities and peak spectra to establish the link between shock evolution and SEP characteristics. The shock nose consistently exhibited higher particle-acceleration efficiency with the largest normal speed, compression ratio, and supercritical Alfven Mach number, while the flanks showed delayed transition to supercritical Alfven Mach number with weaker efficiency. The earliest and most rapid proton enhancement of STEREO-B correlated with efficient shock acceleration and prompt magnetic connectivity to the shock. Spectral analysis revealed that proton energy spectra were consistent with the relativistic diffusive shock acceleration (DSA) estimations. The initial shock acceleration began at about 1.4-5 Rsun and caused the widespread longitudinal SEP distribution. The longitudinal dependence of SEP intensity and spectral variations arise from the combined influence of 3D shock properties, magnetic connectivity, and particle transport processes. The agreement between in situ proton indices and relativistic DSA estimations supports DSA in this SEP event and provides insights into the early-stage acceleration at the source region.

astro-ph.SR↗

arXiv2025

Multiwavelength spectroscopic observations of a quiescent prominence

In this paper we focus on the analysis of the multiwavelength spectroscopic observations of a quiescent prominence. The spectral and geometrical parameters in the prominence were derived and used to constrain the NLTE radiative transfer models. Applying this method with multiwavelength observations provides a good opportunity to reduce the large range of thermodynamic parameters in solar prominences. We used time-slice and optical flow methods in order to derive the plane-of-sky (POS) velocities, and used gravity center and peak position methods on Mg II h&k and H I Ly-alpha profiles to compute the line-of-sight (LOS) velocities. We used the integrated intensities and FWHM values of the H-alpha, Ca II H, and Mg II h&k lines to compare with the NLTE radiative transfer computations. Ionization degree and thickness of the prominence plasma could be further derived. Opposite flows are observed along two strands between prominence barbs. The POS velocity can reach 20 km/s and the largest LOS velocity is > 90 km/s. The derived electron densities range from 6.5e9 cm-3 to 2.7e10 cm-3, and the derived total hydrogen densities range from 7.4e9 cm-3 to 6.6e10 cm-3. The temperature ranges from 7 000 to 14 000 K. The ionization degree of hydrogen is in the range of 0.40 to 0.91. The comparison between averaged and modeled profiles of Mg II and Ly-alpha lines shows that macro-velocities of 15 km/s and 20 km/s are required, respectively. The bulk motions among prominence barbs indicate that the prominence plasma is not confined within magnetic dips but exhibits a large-scale behavior. The presence of high-speed cool plasma flows, along with a wide range of plasma densities and temperatures, suggests that the prominence plasma is far from thermodynamic equilibrium and is inherently dynamic in nature.

astro-ph.SR↗

arXiv2025

Probing Solar Polar Regions

The magnetic fields and dynamical processes in the solar polar regions play a crucial role in the solar magnetic cycle and in supplying mass and energy to the fast solar wind, ultimately being vital in controlling solar activities and driving space weather. Despite numerous efforts to explore these regions, to date no imaging observations of the Sun's poles have been achieved from vantage points out of the ecliptic plane, leaving their behavior and evolution poorly understood. This observation gap has left three top-level scientific questions unanswered, 1) How does the solar dynamo work and drive the solar magnetic cycle? 2) What drives the fast solar wind? 3) How do space weather processes globally originate from the Sun and propagate throughout the solar system? The Solar Polar-orbit Observatory (SPO) mission, a solar polar exploration spacecraft, is proposed to address these three unanswered scientific questions by imaging the Sun's poles from high heliolatitudes. In order to achieve its scientific goals, SPO will carry six remote-sensing and four in-situ instruments to measure the vector magnetic fields and Doppler velocity fields in the photosphere, to observed the Sun in the extreme ultraviolet, X-ray, and radio wavelengths, to image the corona and the heliosphere up to 45 $R_\odot$, and to perform in-situ detection of magnetic fields, and low- and high-energy particles in the solar wind.

astro-ph.SR↗

arXiv2025

The Role of Far-side Magnetic Structures in Modeling 2024 Solar Eclipse

The corona is a crucial region that connects the solar surface to the solar wind and serves as the primary site of solar activity. The 2024 total solar eclipse (TSE) provides a unique opportunity to investigate the large-scale coronal structure. Combined with TSE observations, we study the impact of the magnetic structure of the far-side active region, located in the eastern hemisphere of the Sun that has not yet rotated into the Earth Field-of-View (FoV), on a global Magnetohydrodynamic (MHD) simulation. To address the limitation of single-view measurements in the routine synoptic map, we correct the magnetic field in the far-side region by incorporating full-disk magnetograms measured several days after the TSE, allowing us to capture the temporal evolution of the photospheric magnetic field in near real-time. Simulation results demonstrate that the local magnetic field in the far-side active region can significantly influence the global coronal structure by altering the position of the heliospheric current sheet (HCS), and further affect the global distribution of plasma parameters, even in polar regions. A comparison of the simulation results with white-light (WL) TSE + LASCO C2 observations and in situ measurements by the Parker Solar Probe (PSP) reveals that the composite synoptic map improves the accuracy of coronal modeling. This work provides robust support for advancing our understanding of coronal evolution, as well as deepens the link between the photosphere and large-scale coronal structure. Furthermore, it establishes a theoretical foundation for the future development of multi-view, stereoscopic measurements of the photospheric magnetic field.

astro-ph.SR↗

arXiv2025

Early Evolution of the Cavity and Core of a Coronal Mass Ejection in the Inner Corona

Coronal mass ejections (CMEs) typically exhibit a three-component structure in white-light (WL) coronagraphs. Utilizing the seamless observations of the inner corona ($\le$ 3 R$_\odot$), we have revealed the early evolution of the cavity and core of a CME starting at $\sim$18:20 UT on 2014 October 14. The CME originates from a hot channel (HC), which appears as the bright core and compresses the cavity in WL images. Specifically, most of the dark cavity in WL is filled by bright loop-like structures in 174 Å. The differential emission measure (DEM) analysis indicates that the electron temperature decreases from the core ($\sim$13.4 MK) to the cavity ($\sim$1.35 MK), and the CME cavity is significantly cooler than that enshrouding a prominence ($\ge$ 2 MK). The effective temperature of the cavity increases over time in general, probably due to the compression by the HC expansion. The evolution of the CME bright core includes slow-rise, fast-rise (up to $\sim$330 km s$^{-1}$), and residual-acceleration phases. The cavity exhibits an evolution similar to the core but lags by $\sim$4 minutes, with a lower speed peaking at $\sim$220 km s$^{-1}$. Moreover, the 2D radial speed distribution exhibits the highest speeds at the core apex. The kinematical results further confirm the compression of the cavity. The present event supports the new explanation of the CME structures, i.e., the magnetic flux rope (MFR), which is proxied by the HC, is only responsible for the core, while the cavity is likely a low-density region between the CME front and the MFR.

astro-ph.SR↗

arXiv2025

Intense Hard X-ray Emissions in C-class Flares: A Statistical Study with ASO-S/HXI Data

In the standard model of solar eruptive events, coronal mass ejections (CMEs) and flares are associated with each other through magnetic reconnection initiated by erupting flux ropes. Observations also reveal an increasing association ratio between flares and CMEs with flare intensity. However, the fundamental relationship between flares and CMEs, and that between thermal and nonthermal processes, remains unknown. Here we investigate energetic C-class flares (ECFs) -- Geostationary Operational Environmental Satellite (GOES) C-class flares with hard X-ray (HXR) emissions above 30 keV -- using observations from Advanced Space-based Solar Observatory/Hard X-ray Imager (HXI), Solar Dynamic Observatory, and GOES. Among 1331 C-class flares detected by HXI, 127 ECFs (9.5%) were identified for statistical analysis of their properties and associations with CMEs and other flare-related features. Our statistical results reveal that ECFs have relatively shorter durations and harder spectra (the mean electron power-law index is 4.65), with no significant correlation between soft X-ray flux and nonthermal parameters (e.g., HXR peak flux). Among the 127 events, 53 (42%) were associated with type III bursts, 38 (30%) with jets, at least 13 (~11%) with 360 nm brightenings, and only 5 (~4%) with CMEs. Crucially, all five CME events were narrow CMEs associated with jets. The surprising correlation between these ECFs and CMEs suggests that noneruptive or confined magnetic field configurations in these flares may favor electron acceleration, resulting in harder X-ray spectra.We discuss the potential formation mechanisms and efficient electron acceleration processes in these atypical flares, providing valuable insights into nonstandard flare behavior.

astro-ph.SR↗

arXiv2025

Understanding the Lyα Emission Observed by the Solar Disk Imager Aboard the Advanced Space-based Solar Observatory

The H I Lyman-alpha (Ly$α$) emission, with a wavelength of 1216 Å, is the brightest solar ultraviolet (UV) line. However, comprehensive observations of the Ly$α$ emission line across the full solar disk remain limited. As part of the ASO-S mission, the Solar Disk Imager (SDI) has successfully captured full-disk images in the Ly$α$ band. Gaussian fitting of SDI's spectral response function (SRF) yields a full width at half maximum (FWHM) of approximately 85 Å, which is significantly broader than the distance of Si III line at 1206 Å and the Ly$α$ line. Thus, the emission contribution of Si III to the SDI Ly$α$ passband needs to be considered. For flares, in practice, we calculated the integrated intensity ratio $I$(Si III)/$I$(Ly$α$) by analyzing spectral observations from the SOLSTICE instrument. It yields values between 1.7% and 14.6%. Empirically, the ratio is proportional to the SXR flux. Further analysis of spectral data from the SUMER instrument reveals that the ratio $I$(Si III)/$I$(Ly$α$) is approximately 0.5% for prominences, 0.7%--0.9% for the inner disk, and 1.4%--1.9% close to the limb. These findings suggest that $I$(Si III)/$I$(Ly$α$) is minimal for prominences and the inner disk, and the varying ratios across regions align with the center-to-limb variation of the Si III and Ly$α$ lines. Additionally, we compared Ly$α$ image intensity with 304 Å, 1600 Å, and 1700 Å observations from AIA, as well as H$α$ from CHASE, in multiple regions (a prominence region, two active regions, and a quiet region). A relatively higher correlation of about 85% is found between Ly$α$ and 304 Å in active regions, whereas in the quiet region and prominence, their correlation coefficients are about 55%.

astro-ph.SR↗

arXiv2024

Various Features of the X-class White-light Flares in Super Active Region NOAA 13664

Super active region NOAA 13664 produced 12 X-class flares (including the largest one, an occulted X8.7 flare, in solar cycle 25 so far) during 2024 May 8-15 and 11 of them are identified as white-light flares. Here we present various features of these X-class white-light flares observed by the White-light Solar Telescope (WST) on board the Advanced Space-based Solar Observatory and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory. It is found that both the white-light emissions at WST 3600 Å (Balmer continuum) and HMI 6173 Å (Paschen continuum) show up in different regions of the sunspot group in these flares, including outside the sunspots and within the penumbra and umbra of the sunspots. They exhibit a point-, ribbon-, loop-, or ejecta-like shape, which can come from flare ribbons (or footpoints), flare loops, and plasma ejecta depending on the perspective view. The white-light duration and relative enhancement are measured and both parameters for 3600 Å emission have greater values than those for 6173 Å emission. It is also found that these white-light emissions are cospatial well with the hard X-ray (HXR) sources in the on-disk flares but have some offsets with the HXR emissions in the off-limb flares. In addition, it is interesting that the 3600 and 6173 Å emissions show different correlations with the peak HXR fluxes, with the former one more sensitive to the HXR emission. All these greatly help us understand the white-light flares of a large magnitude from a super active region on the Sun and also provide important insights into superflares on Sun-like stars.

astro-ph.SR↗

arXiv2024

Inflight Performance and Calibrations of the Lyman-alpha Solar Telescope on board the Advanced Space-based Solar Observatory

The Lyman-alpha Solar Telescope (LST) on board the Advanced Space-based Solar Observatory (ASO-S) is the first payload to image the full solar disk and the solar corona in both white-light (WL) and ultraviolet (UV) H I Lya, extending up to 2.5 solar radii (Rs). Since the launch of the ASO-S on 9 October 2022, LST has captured various significant solar activities including flares, prominences, coronal mass ejections (CMEs). LST covers different passbands of 121.6 nm, 360 nm and 700 nm. The Lya Solar Disk Imager (SDI) has a field of view (FOV) of 38.4 arcmin and a spatial resolution of around 9.5 arcsec, while the White-Light Solar Telescope (WST) has a FOV of 38.43 arcmin and a spatial resolution of around 3.0 arcsec. The FOV of the Lya Solar Corona Imager (SCI) reaches 81.1 arcmin and its spatial resolution is 4.3 arcsec. The stray-light level in the 700 nm waveband is about 7.8e-6 MSB (mean solar brightness) at 1.1 Rs and 7.6e-7 MSB at 2.5 Rs, and in the Lya waveband it is around 4.3e-3 MSB at 1.1 Rs and 4.1e-4 MSB at 2.5 Rs. This article will detail the results from on-orbit tests and calibrations.

astro-ph.SR↗

arXiv2024

Asymmetric Hard X-ray Radiation of Two Ribbons in a Thermal-Dominated C-Class Flare

The asymmetry in hard X-ray (HXR) emission at the footpoints (FPs) of flare loops is a ubiquitous feature closely associated with nonthermal electron transport. We analyze the asymmetric HXR radiation at two flare ribbons which is thermal-dominated during a long-duration C4.4 flare that occurred on March 20, 2023, combining multi-view and multi-waveband observations from the ASO-S, SolO, and SDO spacecraft. We find that the H I Ly$α$ emission captures similar features to the He II $λ$304 in both light curve and spatio-temporal evolution of a pair of conjugate flare ribbons. The spectra and imaging analysis of the HXR emission, detected by STIX in 4-18 keV, reveal that the two-ribbon flare radiation is thermal dominated by over 95%, and the radiation source mainly concentrates on the northern ribbon, leading to an asymmetric distribution. To understand the underlying reasons for the HXR radiation asymmetry, we extrapolate the magnetic field within the active region using the NLFFF model. For 78% of the magnetic field lines starting from the northern flare ribbon, their lengths from the loop-tops (LTs) to the northern FPs are shorter than those to the southern FPs. For 62% of the field lines, their magnetic field strengths at the southern FPs exceed those at the northern FPs. In addition, considering the larger density, $\approx1.0\times10^{10}$ cm$^{-3}$, of the low-lying flare loops (< 32 Mm), we find the shorter path from the LT to the northern FP enables more electrons to reach the northern FP more easily after collisions with the surrounding plasma. Therefore, in this thermal-dominated C-class flare, the asymmetric location of the flare LT relative to its two FPs plays a dominant role in the HXR radiation asymmetry, while such asymmetry is also slightly influenced by the magnetic mirror effect resulting in larger HXR radiation at the FPs with weaker magnetic strength.

astro-ph.SR↗

arXiv2024

Association between a Failed Prominence Eruption and the Drainage of Mass from Another Prominence

Sympathetic eruptions of solar prominences have been studied for decades, however, it is usually difficult to identify their causal links. Here we present two failed prominence eruptions on 26 October 2022 and explore their connections. Using stereoscopic observations, the south prominence (PRO-S) erupts with untwisting motions, flare ribbons occur underneath, and new connections are formed during the eruption. The north prominence (PRO-N) rises up along with PRO-S, and its upper part disappears due to catastrophic mass draining along an elongated structure after PRO-S failed eruption. We suggest that the eruption of PRO-S initiates due to a kink instability, further rises up, and fails to erupt due to reconnection with surrounding fields. The elongated structure connecting PRO-N overlies PRO-S, which causes the rising up of PRO-N along with PRO-S and mass drainage after PRO-S eruption. This study suggests that a prominence may end its life through mass drainage forced by an eruption underneath.

astro-ph.SR↗

arXiv2024

Parameter effects on the total intensity of H I Lyα line for a modelled coronal mass ejection and its driven shock

The combination of the H I Lyα (121.6 nm) line formation mechanism with ultraviolet (UV) Lyα and white-light (WL) observations provides an effective method for determining the electron temperature of coronal mass ejections (CMEs). A key to ensuring the accuracy of this diagnostic technique is the precise calculation of theoretical Lyα intensities. This study performs a modelled CME and its driven shock via the 3D MHD simulation. We generate synthetic UV and WL images of the CME and shock to quantify the impact of different assumptions on theoretical Lyα intensities, such as the incident intensity of the Lyα line (Idisk), the geometric scattering function (p(θ)), and the kinetic temperature (Tn) assumed to be equal to the proton (Tp) or electron (Te) temperatures. By comparing differences of the Lyα intensities under these assumptions, we find that: (1) Using the uniform or Carrington maps of the disk Lyα emission underestimates the corona Lyα intensity (< 10%) compared to the synchronic map, except for a slight overestimate (< 4%) in the partial CME core. The Carrington map yields lower uncertainties than the uniform disk. (2) The geometric scattering process has a minor impact on the Lyα intensity, with a maximum relative uncertainty of < 5%. The Lyα intensity is underestimated for the most part but overestimated in the CME core. (3) Compared to the assumption Tn = Tp, using Tn = Te leads to more complex relative uncertainties in CME Lyα intensity. The CME core and void are both overestimated, with the maximum uncertainty in the core exceeding 50% and the void remaining below 35%. In the CME front, both over- and under-estimates exist with relative uncertainties of < 35%. The electron temperature assumption has a smaller impact on the shock, with an underestimated relative uncertainty of less than 20%.

astro-ph.SR↗

arXiv2024

High-resolution Observation of Blowout Jets Regulated by Sunspot Rotation

Coronal jets are believed to be the miniature version of large-scale solar eruptions. In particular, the eruption of a mini-filament inside the base arch is suggested to be the trigger and even driver of blowout jets. Here we propose an alternative triggering mechanism, based on high-resolution H-alpha observations of a blowout jet associated with a mini-filament and an M1.2-class flare. The mini-filament remains largely stationary during the blowout jet, except that it is straddled by flare loops connecting two flare ribbons, indicating that the magnetic arcade embedding the mini-filament has been torn into two parts, with the upper part escaping with the blowout jet. In the wake of the flare, the southern end of the mini-filament fans out like neighboring fibrils, indicative of mass and field exchanges between the mini-filament and the fibrils. The blowout jet is preceded by a standard jet. With H-alpha fibrils moving toward the single-strand spire in a sweeping fashion, the standard jet transitions to the blowout jet. The similar pattern of standard-to-blowout jet transition occurs in an earlier C-class flare before the mini-filament forms. The spiraling morphology and sweeping direction of these fibrils are suggestive of their footpoints being dragged by the leading sunspot that undergoes clockwise rotation for over two days. Soon after the sunspot rotation reaches a peak angular speed as fast as 10 deg/hr, the dormant active region becomes flare-productive, and the mini-filament forms through the interaction of moving magnetic features from the rotating sunspot with satellite spots/pores. Hence, we suggest that the sunspot rotation plays a key role in building up free energy for flares and jets and in triggering blowout jets by inducing sweeping motions of fibrils.

astro-ph.SR↗

arXiv2024

Refinement of global coronal and interplanetary magnetic field extrapolations constrained by remote-sensing and in-situ observations at the solar minimum

Solar magnetic fields are closely related to various physical phenomena on the sun, which can be extrapolated with different models from photospheric magnetograms. However, the Open Flux Problem (OFP), the underestimation of the magnetic field derived from the extrapolated model, is still unsolved. To minimize the impact of the OFP, we propose three evaluation parameters to quantitatively evaluate magnetic field models and determine the optimal free parameters in the models by constraining the coronal magnetic fields (CMFs) and the interplanetary magnetic fields (IMFs) with real observations. Although the OFP still exists, we find that magnetic field lines traced from the coronal models effectively capture the intricate topological configurations observed in the corona, including streamers and plumes. The OFP is lessened by using the HMI synoptic map instead of the GONG daily synoptic maps, and the PFSS+PFCS model instead of the CSSS model. For Carrington Rotation (CR) 2231 at the solar minimum, we suggest that the optimal parameters for the PFSS+PFCS model are $R_{\mathrm{ss}} = 2.2-2.5\ R_{\mathrm{sun}}$ and $R_{\mathrm{scs}} = 10.5-14.0\ R_{\mathrm{sun}}$, as well as for the CSSS model are $R_{\mathrm{cs}} = 2.0 - 2.4\ R_{\mathrm{sun}}$, $R_{\mathrm{ss}} = 11.0 - 14.7\ R_{\mathrm{sun}}$ and $a = 1.0\ R_{\mathrm{sun}}$. Despite the IMFs at 1 AU being consistent with the measurements by artificially increasing the polar magnetic fields, the IMFs near the sun are still underestimated. The OFP might be advanced by improving the accuracy of both the weak magnetic fields and polar magnetic fields, especially considering magnetic activities arising from interplanetary physical processes.

astro-ph.SR↗

arXiv2024

Spectral and Imaging Observations of a C2.3 White-Light Flare from the Advanced Space-Based Solar Observatory (ASO-S) and the Chinese H$α$ Solar Explorer (CHASE)

Solar white-light flares are characterized by an enhancement in the optical continuum, which are usually large flares (say X- and M-class flares). Here we report a small C2.3 white-light flare (SOL2022-12-20T04:10) observed by the \emph{Advanced Space-based Solar Observatory} and the \emph{Chinese H$α$ Solar Explorer}. This flare exhibits an increase of $\approx$6.4\% in the photospheric Fe \textsc{i} line at 6569.2\,Å and {$\approx$3.2\%} in the nearby continuum. The continuum at 3600\,Å also shows an enhancement of $\approx$4.7\%. The white-light brightening kernels are mainly located at the flare ribbons and co-spatial with nonthermal hard X-ray sources, which implies that the enhanced white-light emissions are related to nonthermal electron-beam heating. At the brightening kernels, the Fe \textsc{i} line displays an absorption profile that has a good Gaussian shape, with a redshift up to $\approx$1.7 km s$^{-1}$, while the H$α$ line shows an emission profile though having a central reversal. The H$α$ line profile also shows a red or blue asymmetry caused by plasma flows with a velocity of several to tens of km s$^{-1}$. It is interesting to find that the H$α$ asymmetry is opposite at the conjugate footpoints. It is also found that the CHASE continuum increase seems to be related to the change of photospheric magnetic field. Our study provides comprehensive characteristics of a small white-light flare that help understand the energy release process of white-light flares.

astro-ph.SR↗

arXiv2024

The White-light Emissions in Two X-class Flares Observed by ASO-S and CHASE

The white-light continuum emissions in solar flares (i.e., white-light flares) are usually observed on the solar disk but, in a few cases, off the limb. Here we present on-disk as well as off-limb continuum emissions at 3600 Å (in the Balmer continuum) in an X2.1 flare (SOL2023-03-03T17:52) and an X1.5 flare (SOL2023-08-07T20:46), respectively, observed by the White-light Solar Telescope (WST) on the Advanced Space-based Solar Observatory (ASO-S). These continuum emissions are seen at the ribbons for the X2.1 flare and on loops during the X1.5 event, in which the latter also appears in the decay phase. These emissions also show up in the pseudo-continuum images at Fe I λ6173 from the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO). In addition, the ribbon sources in the X2.1 flare exhibit significant enhancements in the Fe I line at 6569.2 Å and the nearby continuum observed by the Chinese Hα Solar Explorer (CHASE). It is found that the on-disk continuum emissions in the X2.1 flare are related to a nonthermal electron-beam heating either directly or indirectly, while the off-limb emissions in the X1.5 flare are associated with thermal plasma cooling or due to Thomson scattering. These comprehensive continuum observations can provide good constraints on flare energy deposition models, which helps well understand the physical mechanism of white-light flares.

astro-ph.SR↗

arXiv2024

A Statistical Study of Solar White-Light Flares Observed by the White-light Solar Telescope of the Lyman-alpha Solar Telescope on the Advanced Space-based Solar Observatory (ASO-S/LST/WST) at 360 nm

Solar white-light flares (WLFs) are those accompanied by brightenings in the optical continuum or integrated light. The White-light Solar Telescope (WST), as an instrument of the Lyman-alpha Solar Telescope (LST) on the Advanced Space-based Solar Observatory (ASO-S), provides continuous solar full-disk images at 360 nm, which can be used to study WLFs. We analyze 205 major flares above M1.0 from October 2022 to May 2023 and identify 49 WLFs at 360 nm from WST observations, i.e. with an occurrence rate of 23.9%. The percentages of WLFs for M1 - M4 (31 out of 180), M5 - M9 (11 out of 18), and above X1 (7 for all) flares are 17.2%, 61.1%, and 100%, respectively, namely the larger the flares, the more likely they are WLFs at 360 nm. We further analyze 39 WLFs among the identified WLFs and investigate their properties such as white-light enhancement, duration, and brightening area. It is found that the relative enhancement of the white-light emission at 360 nm is mostly (>90%) less than 30% and the mean enhancement is 19.4%. The WLFs' duration at 360 nm is mostly (>80%) less than 20 minutes and its mean is 10.3 minutes. The brightening area at 360 nm is mostly (>75%) less than 500 arcsecond2 and the median value is 225. We find that there exist good correlations between the white-light enhancement/duration/area and the peak soft X-ray (SXR) flux of the flare, with correlation coefficients of 0.68, 0.58, and 0.80, respectively. In addition, the white-light emission in most WLFs peaks around the same time as the temporal derivative of SXR flux as well as the hard X-ray emission at 20 - 50 keV, indicative of Neupert effect. It is also found that the limb WLFs are more likely to have a greater enhancement, which is consistent with numerical simulations.

astro-ph.SR↗

arXiv2023

Partial Eruption of Solar Filaments. I. Configuration and Formation of Double-decker Filaments

Partial eruptions of solar filaments are the typical representative of solar eruptive behavior diversity. Here we investigate a typical filament partial eruption event and present integrated evidence for configuration of the pre-eruption filament and its formation. The CHASE H$α$ observations reveal structured Doppler velocity distribution within the pre-eruption filament, where distinct redshift only appeared in the east narrow part of the south filament region and then disappeared after the partial eruption while the north part dominated by blueshift remained. Combining the SDO, ASO-S observations, and NLFFF modeling results, we verify that there were two independent material flow systems within the pre-flare filament, whose magnetic topology is a special double-decker configuration consisting of two magnetic flux ropes (MFRs) with opposite magnetic twist. During the formation of this filament system, continuous magnetic flux cancellation and footpoint motion were observed around its north end. Therefore, we propose a new double-decker formation scenario that the two MFRs composing such double-decker configuration originated from two magnetic systems with different initial connections and opposite magnetic twist. Subsequent magnetic reconnection with surrounding newly-emerging fields resulted in the motion of footpoint of the upper MFR to the region around footpoint of the lower MFR, thus leading to eventual formation of the double-decker configuration consisting of two MFRs with similar footpoints but opposite signs of magnetic twist. These results provide a potential way to determine unambiguously the progenitor configuration of a partial-eruptive filament and reveal a special type of double-decker MFR configuration and a new double-decker formation scenario.

astro-ph.SR↗