Demonstration of a new python tool for semiautomatic tracing of large-scale coronal waves on the events between May 9th and May 15th 2024

Large-scale coronal waves, also called EIT waves (named after the Extreme Ultraviolet Imaging Telescope on the SOHO satellite they were first observed with), or extreme ultra violet (EUV) waves are fast magnetosonic magnetohydrodynamic waves caused by the fast lateral expansion of coronal mass ejections (CMEs).  They may detach from their driver and are observed as bright fronts crossing large areas of the solar disk. As their initial speed can exceed the local magnetosonic speed, they can develop into large-amplitude waves or even shock fronts, which may be responsible for accelerating solar energetic particle (SEPs).

The EU Horizon project SOLER investigates energetic solar eruptions starting from three perspectives: fast CMEs, strong flares, and large SEP events to improve our understanding on how the eruptive phenomena are linked, how they interact with each other, and how they result in acceleration of high energy particles and their release from the solar corona into interplanetary space.  In this study we present a tool for the analysis of large-scale coronal waves, and demonstrate its outcomes for several events during the May 2024 high activity period.

The Python tool automatically derives the speed and the amplitude evolution of the waves based on perturbation profiles. In order to analyze the imprints of large-scale coronal waves on the lower atmosphere layers, we need to extract the distance of the wave front from its origin for each time step. To do so, the solar full-disk image is split it equidistant circles on the spherical surface around the center of the wave. As estimate of the wave center, we use the position of the associated flare following previous studies. Since large-scale coronal waves usually reveal a non-isotropic propagation, these rings are split up further along the azimuthal direction into different sectors. The analysis is performed on base ratio images (where each image is divided by the same pre-event image), and for each segment the mean intensity value of the pixels is calculated. The segments along each considered propagation direction are combined into intensity profiles along great circles which originate at the flare position, so-called perturbation profiles. A peak finding algorithm marks the peaks and fronts of these perturbation profiles for the wave tracing algorithm. The wave tracing algorithm checks for continuously moving peaks, and applies linear fits to the obtained time-distance profiles to derive the wave speed.

We present the results for multiple waves that were associated with eruptive X- class flares that occurred between the 9^th of May and the 15^th of May 2024, observed by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory. The average wave propagation speeds obtained are in the range from 300 – 800 km/s, with the peaks of the perturbation amplitudes up to 1.4 in the AIA 211 Å filter.

This project has received funding from the European Union's Horizon Europe research and innovation program under grant agreement No 101134999. As part of the grant agreement the tool will be made public.