This work takes advantage of new observational data collected by the High-resolution Coronal Imager (Hi-C) at the highest spatial and temporal resolutions available. This most recent Hi-C dataset is the first to make use of the hot 129 Å channel and the first to consist of targeted observations of a solar flare, rather than the quiescent corona. Images from Hi-C are analysed and compared with complementary EUV observations from SDO/AIA. The widths of the loop strands are measured, and the resulting populations analysed. Preliminary results suggest the majority of loop strands have a width in the range 500-2,000 km, but there is some variation in the loop strand widths observed in plasma at different temperatures. There is some evidence that there are smaller structures present which are partially resolved by Hi-C, with the very smallest smallest loop strands of a similar order of magnitude to the spatial resolution of the Hi-C images. Further results will be presented, as well as a discussion of future work, investigating individual events within the Hi-C observations, making use of the high cadence available to track the dynamic behaviour of the corona.
]]>Understanding how magnetic properties of solar active regions influence coronal mass ejection (CME) dynamics is essential for constraining eruption models and improving space-weather prediction. In this work, we investigate the relationship between magnetic field diagnostics derived from potential-field extrapolations and the 3D speeds of CMEs.
We focus on physically motivated parameters associated with eruption onset, including the critical height of torus instability (hcrit), the strength of the overlying magnetic field strength (Bt), and the flare ribbon flux (Rf). While hcrit and Bt are traditionally evaluated directly above polarity inversion lines (PILs), ; however, identifying PILs can involve threshold-dependent and partially manual selection procedures. To reduce this dependency, we test whether these diagnostics retain predictive power when computed over broader regions of interest (ROIs) within the active region, without relying on explicit PIL selection.
Using decay index profiles derived from photospheric magnetograms, we find a strong correlation between hcrit and CME speed (r ≈ 0.71). When evaluated over progressively larger ROIs centered on the PIL, weighted hcrit from the largest region considered provides the strongest correlation (r ≈ 0.73), indicating that the broader active-region field structure is as informative as measurements strictly above the PIL. In contrast, Bt shows weaker (r = 0.33) predictive capability, and combining it with hcrit offers only marginal improvement. Ribbon flux exhibits moderate correlation (r = 0.44) with CME speed, but the highest predictive power is consistently obtained when hcrit is included.
These results suggest that, within potential-field models, the critical height of torus instability is the dominant magnetic diagnostic of CME speed, and that the large-scale magnetic environment of active regions plays a key role in regulating eruption dynamics.
Huw Morgan
Solar flares are the most energetic manifestations of solar activity and can significantly affect Earth’s magnetosphere, ionosphere, and technological systems. Therefore, anticipating these events remains a fundamental challenge in heliophysics. Soft X-ray observations from the GOES satellites have long been used to monitor and characterize solar flares. Among the various forecasting approaches, the Flare Anticipation Index (FAI), originally proposed by Hudson (2025), has established itself as a promising diagnostic tool for thermal activity preceding flares. The FAI is based on the detection of a Hot Onset Precursor Event (HOPE), characterized by a gradual increase in plasma temperature, and the emission measure before the impulsive phase of a flare. In this work, we performed a statistical validation of the FAI using a representative dataset of approximately 8,000 days between 1980 and 2025. Plasma temperatures and emission measurements were derived from GOES/XRS observations, and FAI-based alerts were generated using predefined thresholds correlated with GOES solar flares within a 30-minute time interval from flare start to peak. A total of 48,344 flares of different classes were analyzed, yielding varying detection rates depending on the flare class. The parameter sets were chosen to minimize the number of false positives and increase the detection rate of large flares (M and X). The results suggest that the FAI is particularly sensitive to medium and large solar flares and has potential for near real-time prediction, while also highlighting the need to optimize the thresholds to improve its predictive performance for each class.
We discuss how to optimise the science output of the European Solar Telescope (EST), when used without the wide-field compensation for high-altitude seeing that the EST multi conjugate adaptive optics (MCAO) will offer. This will likely be the mode of operating EST during its first year, following first light. In this mode, the spatial resolution of a much smaller telescope could surpass that of EST. We propose to operate EST in multi-aperture mode, which will, together with the use of short exposure times and image reconstruction techniques, dramatically improve image quality. In particular, the multi-aperture mode will provide the sustained stable high image quality needed for obtaining time sequences of spectropolarimetric data. The multi-aperture mode is implemented by optically segmenting the 4.2 m aperture into six 1.4 m subapertures by a low-cost modification of the camera lenses of the three Fabry-Perot systems that are expected to be operational soon after first light.
Coronal bright points are ubiquitous, highly energetic events that are often seen accompanying other dynamic and eruptive phenomena in the solar atmosphere. Their large energy output, their similarity to active regions and their connections to other events make them especially interesting to understand the solar corona. This talk will describe the findings of a recent project focusing on the hottest loop constituents of coronal bright points. We extract and analyse the hot loops of three different state-of-the-art radiative-MHD Bifrost simulations, studying their basic thermodynamic, magnetic and geometrical properties. The simulated loop properties are compared to a recent observational dataset, the first detailed study of this kind found in the literature, finding great compatibility between simulations and observations. Additionally, the loop geometry is assessed by focusing on the deviations from the commonly-assumed semi-circularity, another aspect that has been overlooked so far. We study the heating and cooling mechanisms acting on the loops, a fundamental aspect to accurately model the energy balance of these structures and their contribution to the coronal heating. The results show that only the 3D simulations show strong Joule and viscous heating in the footpoints. This reveals a localized source of entropy possibly stemming from 3D magnetic reconnection at the footpoints, which is consistent with other findings in this work.
On 26 September 2022, we observed a quiescent solar prominence with Hα imaging spectroscopy using the Solar Dynamics Doppler Imager (SDDI) on the SMART telescope. Unlike earlier works that detected 4- and 15-min oscillations through long-slit, 1D wavelet methods, we adapt the wavelet analysis to 3D data to explore the full prominence structure. Complementary data from SDO/AIA (304 Å, 171 Å) STEREO-A/EUVI (304 Å), and Solar Orbiter EUI/FSI (304 Å, 174 Å) enable a multi-view, multi-thermal investigation of wave periodicity across the prominence. Our aim is to characterize how oscillatory periods are distributed in plasma at different temperatures and viewing angles, thereby assessing wave propagation and variability throughout the prominence body.
During a solar flare, fluxes in various lines and continua of the solar spectrum increase, causing enhanced ionisation in the illuminated part of the Earth’s ionosphere and an increase in the total electron content (TEC). The dynamics of TEC driven by the impulsive phase of solar flares have been studied extensively through both modelling and experimental measurements. However, the ionospheric effects of the late phase of solar flares, which occur in nearly half of X-class flares, were discovered only in 2024. This talk presents the results of the first multi-event study of the ionospheric response to the late phase of X-class solar flares. It also investigates how the flare’s location on the solar disk affects the ratio of ionospheric responses between the impulsive and late phases.
Spicules are ubiquitous, small-scale plasma jets that populate the lower solar atmosphere. They are seen prominently in chromospheric observations and also exhibit signatures in the transition region and lower corona. More recently, these highly dynamic spicular jets in observations have been reported to be associated with upward propagating EUV intensity perturbations in the corona. A similar link has been found in previous simulations. This can have important implications for understanding mass and energy transport in the solar atmosphere. However, the physical origin and properties of these Propagating Coronal Disturbances (PCDs), and their spicular connection, are not yet fully understood. In this ongoing work, we explore the connection of PCDs with spicules by performing 2D radiative MHD simulations using the Pencil Code, where a forest of spicules is self-consistently produced in the solar atmosphere powered by the subsurface convective processes. By using the technique of Lagrangian tracking on the simulated snapshots, we find that the convection generates “acceleration fronts” by several mechanisms, including, for example, (1) squeezing by granular buffeting, (2) collapse of granules, and (3) solar global modes, aided by magnetic reconnection. These acceleration fronts are also regions of strong compression or shocks that propagate outward through the solar atmosphere at the speed of slow magneto-acoustic waves. The passage of shock fronts successively through any point in the atmosphere produces saw-toothed velocity signals. We analyze wavelet power spectra for these modeled velocity signals sampled at several atmospheric heights in the simulations, along with other diagnostics, and use them to investigate how the slow MHD shock waves may be the common driver behind both PCDs and spicules.
Sahel Dey, Piyali Chatterjee, Robertus Erdélyi
In July 2024, Sunrise III flew from Sweden to Canada at stratospheric heights capturing high resolution diffraction-limited images of the Sun for 6.5 days. The telescope carried three scientific instruments each complementing the other by observing in different parts of the solar spectrum from the near-ultraviolet by SUSI (309 nm - 417 nm), the visible by TuMag (517 nm - 525 nm) to the near infrared by SCIP (765 nm - 855 nm). During its flight, Sunrise III observed a wide variety of features on the Sun including the quiet region, sunspots, plages, filaments, spicules, flux emergence, and also flares. By combining the data from the three instruments, it is possible to infer and understand various properties of the solar atmosphere from the photosphere to the upper chromosphere. In this talk, I will walk you through the Sunrise III journey, the science planning, present observational highlights and provide a glimpse into some of the exciting ongoing scientific analysis from the Sunrise III data.
A. Korpi-Lagg, A. Gandorfer, S. K. Solanki, A. Feller, J.C. del Toro Iniesta, D. Orozco, Y. Katsukawa, T. Berkefeld, P. Bernasconi, T. Riethmüller and the Sunrise III Team
Active regions with increasing magnetic complexity are more likely to trigger major solar eruptions. During a single solar cycle, approximately 1000 active regions emerge on the Sun. Among these, about 250 develop magnetically complex configurations, but only ~10% of them go on to produce major eruptive events.
This presentation addresses the challenge of bridging short- and medium-term analyses of solar magnetic field evolution to improve our ability to identify which of these complex active regions are most likely to erupt. Specifically, we focus on how the location and magnetic evolution of these regions can help us isolate the small fraction (~10%) of magnetically complex active regions that eventually produce major eruptions.
The analysis of the longitudinal distribution of these eruptive active regions carried out builds on the concept of active longitudes, as introduced in Kornél Császár’s earlier ESPOS talk in this semester. In the second part of the talk, we present studies of the magnetic field evolution in the lower solar atmosphere for selected magnetically complex active regions that emerged within the identified active longitude band. Using approximately ten magnetic proxy parameters, we examine how the evolution of their structure provides insight into their eruptive potential.