European Solar Physics Online Seminar Archiv

Stellar flares cannot be spatially resolved, which means that we have to extract complex three-dimensional behavior from a one-dimensional disk-integrated spectrum. Due to their proximity to Earth, solar flares can serve as a stepping stone for understanding their stellar counterparts, especially when using a Sun-as-a-star instrument in combination with spatially resolved observations. In this talk I will discuss a confined X2.2 flare and its eruptive X9.3 successor as measured by the HARPS-N Sun-as-a-star telescope. The behavior of multiple photospheric and chromospheric spectral lines are investigated by means of activity indices and contrast profiles, which are then related to physical processes directly observed in high-resolution observations made with the Swedish 1-meter Solar Telescope (SST). We further explore these relations by using the newly developed Numerical Sun-as-a-Star Integrator (NESSI) code to convert high-resolution SST flares to full disk spectra. Our findings suggest a relationship between the evolving shapes of the disk integrated spectra and the flare locations on the solar disk, which could be act as a guide for constraining flare locations in stellar spectra. [mehr]

In the recent decades, three-dimensional modelling of solar flares and eruptions has made a number of predictions that were subsequently indicated by high-resolution imaging observations. These include existence of magnetic reconnection geometries involving the erupting flux rope itself, which drifts as a result, and also the apparent slipping and slip-running motion of footpoints of individual reconnecting structures. In this talk, we will summarize the predictions of the MHD models as well as the corroborating evidence, with particular emphasis on recent observations of super-Alfvénic slippage of flare kernels. [mehr]

The Sun is a dynamic star, displaying activities ranging from subtle, short-lived events to major coronal mass ejections (CMEs) and powerful flares. Differentiating between “flaring” and “non-flaring” active region (AR) configurations is critical for heliophysics research. This study investigates whether small to medium-scale activity in ARs holds clues about their eruptive potential and future behaviour. Using data from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO), we analyse transient brightenings and their relationship to the magnetic polarity inversion line (PIL) in ARs. We observe significant differences between pre-flaring and non-flaring ARs in terms of the spatial distribution and temporal evolution of transient brightenings around the PIL. Key parameters include the number, intensity, and magnetic flux of brightenings over time, as well as their behaviour across multiple wavelengths. These variations offer insights into the Sun’s atmospheric dynamics and the mechanisms driving major flares and – in case of coronal mass ejections – eruptions. By understanding the pre-eruptive activity in ARs, we aim to improve solar event prediction capabilities and advance our knowledge of the relevant dynamics. [mehr]

On October 28, 2021 the first X-class solar flare of Solar Cycle 25 occurred in active region NOAA AR 12887 with a peak at 15:35 UT. It produced the rare event of ground-level enhancement of the solar relativistic proton flux and a global extreme ultraviolet wave, along with a fast halo coronal mass ejection (CME) as seen from Earth’s perspective. A few hours before the flare, a slower CME had erupted from a quiet Sun region just behind the northwestern solar limb. Solar Orbiter was almost aligned with the Sun-Earth line and, during a synoptic campaign, its coronagraph Metis detected the two CME events in both Visible Light (VL) and UltraViolet (UV) channels. The earlier CME took place in the north-west (NW) sector of Metis field of view, while several bright features of the flare-related event appeared mostly to the south-east (SE). The NW and SE events have two distinct origins, but were both characterized by a very bright emission in HI Ly-alpha visible in the UV images of Metis up to 8 solar radii. This work is a follow-up study of two out of the six events analyzed by Russano et al. 2024 (A&A, 683, A191), aimed at investigating the evolution of these two almost co-temporal CMEs but originating in such distinct source regions. To that end, we extensively inspect data sets from numerous remote-sensing instruments observing the Sun in several spatial and spectral regimes. We characterize several aspects of these CMEs, including their three-dimensional properties, kinematics, mass, and temporal evolution of those quantities. Results of this work point to notable differences between these two events showing significant UV emission in the corona. Co-authors: H. Cremades, F. A. Iglesias, L. Teriaca, R. Aznar Cuadrado, F. M. López, L. Di Lorenzo, M. Temmer, M. Romoli, D. Spadaro, and the Metis Team [mehr]