Transverse Vertical Oscillations During the Contraction and Expansion of Coronal Loops

Abstract

In this paper, we carry out a detailed analysis of the M1.6 class eruptive flare occurring in NOAA active region 13078 on 2022 August 19. The flare is associated with a fast coronal mass ejection (CME) propagating in the southwest direction with an apparent speed of ∼926 km s−1. Meanwhile, a shock wave is driven by the CME at the flank. The eruption of the CME generates an extreme-ultraviolet (EUV) wave expanding outward from the flare site with an apparent speed of ≥200 km s−1. As the EUV wave propagates eastward, it encounters and interacts with the low-lying adjacent coronal loops (ACLs), which are composed of two loops. The compression of the EUV wave results in contraction, expansion, and transverse vertical oscillations of ACLs. The commencements of contraction are sequential from western to eastern footpoints and the contraction lasts for ∼15 minutes. The speeds of contraction lie in the range of 13–40 km s−1 in 171 Å and 8–54 km s−1 in 193 Å. A long, gradual expansion follows the contraction at lower speeds. Concurrent vertical oscillations are superposed on the contraction and expansion of ACLs. The oscillations last for two to nine cycles and the amplitudes are ≤4 Mm. The periods are between 3 and 12 minutes with an average value of 6.7 minutes. The results show rich dynamics of coronal loops.