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.

Context. The widespread longitudinal distribution of solar energetic particles (SEPs) is influenced by magnetic connectivity from the observers to coronal mass ejection (CME)-driven shocks. This connectivity determines shock properties encountered by magnetic-field lines, which in turn regulate the initial particle injection and acceleration efficiency. Aims. We aim to investigate the relationship between the spatial–temporal evolution of shock properties and the longitudinal dependence of SEP intensities and spectra. Methods. The shock parameters, including the normal speed, oblique angles, compression ratio, and Alfvén 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. Results. The shock nose consistently exhibited higher particle-acceleration efficiency with the largest normal speed, compression ratio, and supercritical Alfvén Mach number, while the flanks showed delayed transition to supercritical Alfvén 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. Conclusions. The initial shock acceleration began at about 1.4 ∼ 5 R⊙ 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.

Imaging observations of solar X-ray bursts can reveal details of the energy release process and particle acceleration in flares. Most hard X-ray imagers make use of the modulation-based Fourier transform imaging method, an indirect imaging technique that requires algorithms to reconstruct and optimize images. During the last decade, a variety of algorithms have been developed and improved. However, it is difficult to quantitatively evaluate the image quality of different solutions without a true, reference image of observation. How to choose the values of imaging parameters for these algorithms to get the best performance is also an open question. In this study, we present a detailed test of the characteristics of these algorithms, imaging dynamic range and a crucial parameter for the CLEAN method, clean beam width factor (CBWF). We first used SDO/AIA EUV images to compute DEM maps and calculate thermal X-ray maps. Then these realistic sources and several types of simulated sources are used as the ground truth in the imaging simulations for both RHESSI and ASO-S/HXI. The different solutions are evaluated quantitatively by a number of means. The overall results suggest that EM, PIXON, and CLEAN are exceptional methods for sidelobe elimination, producing images with clear source details. Although MEM_GE, MEM_NJIT, VIS_WV and VIS_CS possess fast imaging processes and generate good images, they too possess associated imperfections unique to each method. The two forward fit algorithms, VF and FF, perform differently, and VF appears to be more robust and useful. We also demonstrated the imaging capability of HXI and available HXI algorithms. Furthermore, the effect of CBWF on image quality was investigated, and the optimal settings for both RHESSI and HXI were proposed.

Aims. 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 nonlocal thermodynamic equilibrium (NLTE) radiative transfer models of the prominence. Applying this method with multiwavelength observations provides a good opportunity to reduce the large range of thermodynamic parameters in solar prominences. Methods. As far as velocities are concerned, we used time-slice and optical flow methods in order to derive the plane-of-sky (POS) velocities in the prominence, 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. As far as densities and temperatures are concerned, we used the integrated intensities and full width at half maximum (FWHM) values of the H alpha and the CaII H together with Mg II h&k lines to compare with values derived from the NLTE radiative transfer computations. Ionization degree and thickness of the prominence plasma could be further derived. Results. Opposite flows are observed along two strands between prominence barbs. The POS velocity can reach 20 km s(-1) and the largest LOS velocity is > 90 km s(-1). The derived electron densities range from 6.5 x 10(9) to 2.7 x 10(10) cm(-3) and the derived total hydrogen densities range from 7.4 x 10(9) to 6.6 x 10(10) cm(-3) in different regions of the studied prominence. The temperature ranges from 7000 to 14000 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 and 20 km s(-1) are required, respectively. Conclusions. 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.

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 weak 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.

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 I (Si iii)/ I (Ly α ) is approximately 0.5 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 α and 304 Å in active regions, whereas in the quiet region and prominence, their correlation coefficients are about 55

Photon sieve (PS), a diffractive optical element, has significant application potential in ultraviolet and X-ray imaging, as well as large-aperture visible-light imaging, owing to its low manufacturing complexity. However, evaluating the performance of a PS with practical application value is challenging because it typically contains 10 8-10 9 pinholes, making simulations computationally intensive. To address this challenge, we propose a high-efficiency parallelized algorithm based on GPU acceleration and individual far-field models, achieving a 10x speedup over a 96-core CPU implementation with comparable computational cost. We also discuss the high-order off-axis correction term for individual far-field models. Using these improvements, we develop a comprehensive simulation program capable of analyzing multi-field-of-view imaging performance under both ideal and non-ideal conditions, including factors such as chromatic aberration, depth of focus, wrinkles, and manufacturing uncertainties. To demonstrate its utility, we apply the program to analyze a ground-testing system for a space telescope. This study not only advances the theoretical understanding of the PS imaging but also provides a powerful tool for designing and optimizing the PS-based optical systems.

Solar erupting prominences occasionally experience the splitting due to their interaction with ambient magnetic fields, yet the detailed process of the interaction remains elusive. As a result of the splitting, the significant part of prominence mass can evolve as a core of the associated coronal mass ejection (CME), while the rest of prominence mass is often transferred to and trapped in the nearby loop structure. Combining the high-quality multi-wavelength observations from SDO, ASO-S, FY-3E, and CALLISTO, we report an intriguing case of the splitting of an erupting prominence that occurred on 2023 December 31, and the splitting brought two different components of the core of the following CME, just like the “double-bang firecracker”. During the splitting, the prominence apparently deflected southward from the initial quasi-radial direction and abruptly accelerated from ∼180 to ∼810 km s−1. Meanwhile, an unexpected newly-formed loop structure emerged from behind the ejecting prominence and propagated slowly along the quasi-radial direction. All results suggest that the inclined ejecting prominence and the quasi-radially propagating loop structure contributed to two separate components of the CME core. It is likely that the erupting prominence experienced external reconnection with nearby arcades, which resulted in the prominence splitting and the formation of the new loop structure that slowly erupted. The pseudostreamer configuration is proposed to play an important role in the case of “double-bang firecracker”.

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: How does the solar dynamo work and drive the solar magnetic cycle? What drives the fast solar wind? How do space weather processes globally originate from the Sun and propagate throughout the solar system? The Solar Polarorbit 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 observe the Sun in the extreme ultraviolet, X-ray, and radio wavelengths, to image the corona and the heliosphere up to 45 Rs, and to perform in-situ detection of magnetic fields,and low-and high-energy particles in the solar wind. The SPO mission is capable of providing critical vector magnetic fields and Doppler velocities of the polar regions to advance our understanding of the origin of the solar magnetic cycle, providing unprecedented imaging observations of the solar poles alongside in-situ measurements of charged particles and magnetic fields from high heliolatitudes to unveil the mass and energy supply that drive the fast solar wind, and providing observational constraints for improving our ability to model and predict the three-dimensional(3D) structures and propagation of space weather events.

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 farside active region, located in the eastern hemisphere of the Sun that has not yet rotated into the Earth field of view, on a global magnetohydrodynamic simulation. To address the limitation of single-view measurements for the routine synoptic map, we correct the magnetic field in the farside 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 farside active region can significantly influence the global coronal structure, by altering the position of the heliospheric current sheet, and further affect the global distribution of plasma parameters, even in polar regions. A comparison of the simulation results with white-light TSE + Large Angle and Spectrometric Coronagraph C2 observations and in situ measurements by the Parker Solar Probe reveals that the composite synoptic map improves the accuracy of the coronal modeling. This work provides robust support for advancing our understanding of coronal evolution, as well as deepening the link between the photosphere and large-scale coronal structure. Furthermore, it establishes a theoretical foundation for the future development of multiview stereoscopic measurements of the photospheric magnetic field.

Coronal mass ejections (CMEs) typically exhibit a three-component structure in white-light (WL) coronagraphs. Utilizing the seamless observations of the inner corona (≤3 R _⊙ ), we have revealed the early evolution of the cavity and core of a CME starting at ∼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 analysis indicates that the electron temperature decreases from the core (∼13.4 MK) to the cavity (∼1.35 MK), and the CME cavity is significantly cooler than that enshrouding a prominence (≥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 ∼330 km s ^−1 ), and residual-acceleration phases. The cavity exhibits an evolution similar to the core but lags by ∼4 minutes, with a lower speed peaking at ∼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.

Cross-calibration of X-ray instruments is crucial for stereoscopic studies of solar hard X-ray directivity and three-dimensional morphology, where spectral and imaging differences observed from multiple perspectives provide critical constraints. We present the preliminary results of the spectral calibrations of ASO-S/HXI through internal consistency checks of its three total flux detectors and cross-calibrations with Solar Orbiter/STIX, Fermi/GBM, and Konus-Wind data. Both calibration tests suggest that the response matrix of one of the HXI total flux monitors, D94 (with a thin aluminum window), needs to be modified. The new response matrix is determined by testing the series of response matrices with changing effective aluminum thickness through simulations. Post-correction analysis reveals ∼ 88% of co-observed events demonstrate electron spectral index consistency within ± 0.5 , while comparisons of the total counts above 30 keV show < 10

Indirect X-ray modulation imaging has been adopted in a number of solar missions and provided reconstructed X-ray images of solar flares that are of great scientific importance. However, the assessment of the image quality of the reconstruction is still difficult, which is particularly useful for scheme design of X-ray imaging systems, testing and improvement of imaging algorithms, and scientific research of X-ray sources. Currently, there is no specified method to quantitatively evaluate the quality of X-ray image reconstruction and the point-spread function(PSF) of an X-ray imager. In this paper, we propose percentage proximity degree(PPD) by considering the imaging characteristics of X-ray image reconstruction and in particular, sidelobes and their effects on imaging quality. After testing a variety of imaging quality assessments in six aspects, we utilized the technique for order preference by similarity to ideal solution to the indices that meet the requirements. Then we develop the final quality index for X-ray image reconstruction, QuI X,which consists of the selected indices and the new PPD. QuI X performs well in a series of tests, including assessment of instrument PSF and simulation tests under different grid configurations, as well as imaging tests with RHESSI data. It is also a useful tool for testing of imaging algorithms, and determination of imaging parameters for both RHESSI and ASO-S/Hard X-ray Imager, such as field of view, beam width factor, and detector selection.

Abstract We present an automated solar flare detective, a software tool to automatically process solar observation images, detect and track solar flares, and finally compile an event catalog. It is capable of identifying and tracking flares that happen simultaneously or temporally close together. The method to identify a flare is based on the local intensity changes in macropixels. The basic characteristics such as the time and location information of a flare are determined with a triple-threshold scheme, with the first threshold (global threshold) to determine the occurrence (location) of the flare, and the second/third threshold (local threshold) to determine the start/end time of the flare. We have applied this tool to one month of continuous solar ultraviolet (UV) images obtained by the Solar Disk Imager (SDI) onboard the Advanced Space-based Solar Observatory (ASO-S), which show solar activities such as flare, filament/prominence, and solar jets. Our automated tool efficiently detected a total number of 226 solar events. After a visual inspection, we found that only one event was misidentified (not related to solar activities). We compared the detected events with the GOES X-ray flare list and found that our tool can detect 73\% of GOES M-class and above flares (37 out of 51), from which we conclude that the intensity increase in SDI UV images can be considered as a good indicator of a solar flare.

Prominences are important features in the solar atmosphere. Their activities often develop into solar eruptions, such as flares and/or coronal mass ejections. We report here on observations of activities of two crossing prominences and the resulting oscillations observed with the Advanced Space-based Solar Observatory (ASO-S) and the Solar Dynamics Observatory. We observed the two crossing prominences rising simultaneously with a speed of about 100 km s−1. The lower-lying prominence consists of threads that show increase of writhe during the rising process. We find evidence that the writhe of the lower-lying prominence is transferred into the overlying one. This transfer of writhe leads to a failure of the eruption of the lower-lying prominence and a shearing motion of the legs of the overlying prominence. The failed eruption of the lower-lying prominence also triggers kink oscillations of its threads, which show periods of about 300 s and amplitudes of less than 10 Mm. Such oscillations are considered to be intrinsic mode and can help to probe the magnetic field of the prominence. Our observations support the idea that the transfer and release of writhe play an important role in confining eruptions of a prominence, and interactions among prominences/filaments might be a crucial aspect of a solar eruption.

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, 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.

We present an automated solar flare detection software tool to automatically process solar observed images, detect and track solar flares, and finally compile an event catalog. It can identify and track flares that happen simultaneously or temporally close together. The method to identify a flare is based on the local intensity changes in macropixels. The basic characteristics, such as the time and location information of a flare, are determined with a triple-threshold scheme, with the first threshold (global threshold) to determine the occurrence (location) of the flare and the second and third thresholds (local thresholds) to determine the real start and end times of the flare. We have applied this tool to one month of continuous solar ultraviolet (UV) images obtained by the Solar Disk Imager (SDI) onboard the Advanced Space-based Solar Observatory (ASO-S), which show active phenomena such as flares, filaments or prominences, and solar jets. Our automated tool efficiently detected a total number of 226 solar events. After a visual inspection, we found that only one event was misidentified (unrelated to an active event). We compared the detected events with the GOES X-ray flare list and found that our tool can detect 81% of GOES M-class and above flares (29 out of 36), from which we conclude that the intensity increase in SDI UV images can be considered as a good indicator of a solar flare.

The solar wind has been extensively studied recently with in situ observations, and the understanding of its counterpart near the solar surface has also progressed significantly. With the spectroscopic observations from the Chinese H α Solar Explorer (CHASE), the chromospheric Dopplergram of the full solar disk is first obtained almost simultaneously. By investigating the statistics of the Doppler velocities at the chromosphere, we find that the coronal hole (CH) regions are dominated by Doppler blueshifts, with a stronger net magnetic flux region corresponding to smaller blueshift velocity. In addition to the average blueshift, the probability density of the Doppler shift is not symmetrically distributed but shows an excess at the redshift side, while the reference region does not show such an asymmetry. The redshift asymmetry may provide a possible clue for the interchange reconnection that might happen just above the chromosphere. By sampling the regions at the network boundaries in the CHs, the probability density is slightly enhanced at the parts of both larger blueshifts and redshifts compared with the result for the whole CH region. As the reference region also shows such enhancement, the crucial area associated with the origin of solar wind is not identified efficiently by sampling the overall network boundaries as demonstrated here. The present study shows the first attempt at interpreting the origin of solar wind in the transient CHs based on the CHASE spectroscopic observations, and a combination of full-disk and high-resolution observations is helpful in the future for firmly understanding the source region of solar wind.