Guided Propagation of a Shock in the Low Solar Corona

Together with colleagues, we studied an impulsive X-class flare from May 10, 2022, where both a faint CME and EUV wave were observed (Rigney et al., 2024). We studied the characteristics of the radio emission, the propagation of the EUV wave and the relation between both phenomena. As the dynamic spectrum in Figure 1 shows, a type II radio burst was recorded which lasted for approximately 25 minutes. The type II burst displayed a band-split in both the fundamental and harmonic bands. The on-disk signatures of the global EUV wave were identified using observations from the AIA onboard the SDO. The wavefront was highly directional, propagating mainly to the north-east of the erupting active region, with some indication of wavefront propagation to the south of the active region, similar to the observed radio emission.

Fig. 1 – Upper Panel: I–LOFAR dynamic spectrum of the Type II radio burst on May 10, 2022, showing the bright fundamental and harmonic bands. The fundamental band drifts from ∼60 MHz to ∼25 MHz over 10 minutes, with band–splitting occurring within both the fundamental and harmonic lanes. Dashed vertical lines correspond to timestamps of images in the lower panel. Lower Panel: Motion of the 150 MHz NRH radio imaging overlaid on an AIA three–channel difference image showing the motion of the EUV wave. A solid red line marks the EUV front.

Radio imaging data sampled at 10 second cadence and 154 MHz and 408 MHz was obtained from the NRH. Two clear radio sources on the solar disk were observed propagating away from the active region for a short time after the flare. The southward propagating emission quickly faded after approximately 40 s. The northward propagating emission was observed for approximately 7 min, with clear motion of the peak along the axis of propagation of the EUV wave. The velocity of the EUV wave-front was measured accounting for the propagation across the spheroidal solar surface. Two methods were used to estimate this velocity, CorPITA (Long et al. 2014) and Wavetrack (Stepanyuk et al. 2022). Figure 2 shows the application of Wavetrack to the EUV wave front. The mean velocity of the wave as obtained by CorPITA is 450 km/s, while the more detailed Wavetrack obtained a mean velocity of 700 km/s. The two methods give results that agree within the error margins.

Fig. 2 – Application of Wavetrack to the May 10, 2022 coronal wave. Top panel – segmented masks show the very wide and persistent front moving in the north-east direction. Bottom panel – maps of estimated velocities obtained by applying the FLCT algorithm to Wavetrack maps.