Speaker
Description
Coronal mass ejections are well-established drivers of large-scale wave phenomena in the low corona, yet the wave dynamics operating in the extended corona and inner heliosphere have remained almost entirely unexplored. We report here the first combined observational and numerical evidence of coherent, global compressive oscillations propagating through the outer corona and inner heliosphere. Our analysis is supported by both observational data from the SOHO/LASCO C3 coronagraph and a state-of-the-art magnetohydrodynamic (MHD) simulation that reproduces the large-scale coronal and heliospheric conditions of the event. To extract wave signatures from the complex coronal brightness data containing multiple concurrent phenomena, we employ Spectral Proper Orthogonal Decomposition (SPOD). This method can effectively decompose the perturbations in the original signal into modes that capture a physically distinct, energetically ranked oscillation at a single temporal frequency. Applying this framework to the extreme coronal mass ejection event of 2012 July 23, we isolate two physically distinct wave signatures. The first is a fast-mode shock-like compressive wave propagating preferentially along the CME propagation axis, with speeds exceeding 1000 km s⁻¹, that dissipates within approximately 2.5 hours, consistent with strong local damping or rapid energy transfer to the surrounding plasma. The second, more remarkable, is a large-scale global circular wavefront that persists for approximately 7 hours across the full LASCO C3 field of view. This behavior is fully consistent with fast-mode MHD wave propagation in a low-beta coronal plasma, where magnetic pressure dominates, and compressive disturbances travel coherently over vast distances with minimal dispersion. This second mode constitutes the first observational detection of a global-scale oscillation of this kind in the outer corona. Both wave signatures are independently recovered from SPOD applied to synthetic white-light data and directly from the MHD variables, confirming the physical interpretation. The compressive front spans approximately 60°-90° around the CME nose, while the global mode extends across nearly the full 360° angular extent of the C3 field of view. The analysis of synthetic white-light data further suggests that such wave signatures should be detectable with future missions such as PUNCH. These findings reveal a previously unrecognized component of CME-driven wave activity operating on spatial and temporal scales far beyond what has been characterized to date, providing new physical constraints on energy transport and plasma structuring in the extended corona and inner heliosphere.