Overexpansion-dominated coronal mass ejection formation and induced radio bursts

Abstract

Aims. Coronal mass ejections (CMEs) are the most fascinating explosions in the Solar System. Their formation is still not fully understood, however. Methods. We investigated a well-observed CME on 2021 May 7 that showed a typical three-component structure and was continuously observed from 0 to 3 R ⊙ by a combination of SDO/AIA (0-1.3 R ⊙ ), PROBA2/SWAP (0-1.7 R ⊙ ), and MLSO/K-Cor (1.05-3 R ⊙ ). Furthermore, we compared the morphological discrepancy between the CME white-light bright core and the extreme-UV (EUV) blob. We finally explored the origin of various radio bursts that are closely related to the interaction of the CME overexpansion with a nearby streamer.Results. An interesting finding is that the height increases of the CME leading front and of the bright core are dominated by the overexpansion during the CME formation. The aspect ratios of the CME bubble and bright core, quantifying the overexpansion, are found to decrease as the SO/STIX 4-10 keV and GOES 1-8 Å soft X-ray flux of the associated flare increases near the peaks. This indicates that the flare reconnection plays an important role in the first overexpansion. The CME bubble even undergoes a second overexpansion, although it is relatively weak, which is closely related to the compression with a nearby streamer and likely arises from an ideal magnetohydrodynamics process. Moreover, the CME EUV blob is found to be relatively lower and wider than the CME white-light bright core, which may correspond to the bottom part of the growing CME flux rope. The interaction between the CME and the streamer leads to two type II radio bursts, one that is drifting normally and another that is stationary, which are speculated to be induced by two different sources of the CME-driven shock front. The bidirectional electrons shown in series of C-shaped type III bursts suggest that the interchange reconnection is also involved during the interaction of the CME and streamer.

The Structure of Coronal Mass Ejections Recorded by the K-Coronagraph at Mauna Loa Solar Observatory

“…Figure 3 displays a CME induced by the hot-channel eruption as revealed with the AIA 131 Å observation in panel (a). This event occurred on 2021 May 7 (Event 45 in Table 1) and a previous study (Wang et al 2022) has demonstrated that the hot channel evolved into the bright core in the K-COR image as shown in panel (b). The three-part feature is distinguishable directly in the static image; thus no dashed lines are a guide for the eye in this panel.…”

“…However, recent studies pointed out that the traditional opinion is questionable, because some three-part CMEs are not associated with prominence eruptions at all (Howard et al 2017;Song et al 2017Song et al , 2019bWang et al 2022;Song et al 2023). Based on dual-viewpoint and seamless observations from the inner to outer corona, a new explanation on the threepart nature has been proposed, in which the bright frontal loop is formed due to the compression as the magnetic loops are successively pushed to stretch up by the underlying MFR (Low 2001;Chen 2009), the core can correspond to the MFR and/or prominence, and the dark cavity between the CME front and the MFR is a low-density zone with a sheared magnetic field (Song et al 2017(Song et al , 2019a.…”

Numerical Simulation on the Leading Edge of Coronal Mass Ejection in the Near-Sun Region

“…The presence of the HCB suggests that it could be the physical mechanism of the CME front. Furthermore, we suggest it may also be responsible for the nonwave component of the EUV disturbance, according to the bimodal interpretation of the EUV disturbance (Shibata & Magara 2011;Warmuth 2015).…”

“…The cores of CMEs used to be interpreted as eruptive filaments according to the corresponding photospheric magnetogram and multiband observations (Gopalswamy et al 2006). However, recent works challenge the filament-core connections for some events (Howard et al 2017;Song et al 2017Song et al , 2019aSong et al , 2022Song et al , 2023Wang et al 2022). They found that more than half of the three-part CMEs are not associated with filaments, and speculated that the geometrical projection of the eruptive MFR may also produce CME cores.…”

Sequential Remote Brightenings and Co-spatial Fast Downflows during Two Successive Flares

“…It was also suggested that interchange reconnection may occur between the CME magnetic flux rope (MFR) and the open field during the eruption, which facilitates the escape of energetic particles (e.g., . Two pieces of indirect evidence for this are observations of type III radio bursts that are caused by escaped electron beams, in particular for those extending to the wavelength of decameterkilometer (van Driel-Gesztelyi et al 2008;Reid & Ratcliffe 2014;Kou et al 2020;Wang et al 2022), and intense solar energetic particles that arrive at the Earth and cause space weather effects (Masson et al 2012(Masson et al , 2013. Moreover, interchange reconnection is also able to produce the leakage of filament materials once the eruption involves filaments, as well as the drifting of filament footpoints (Aulanier & Dudík 2019;Yan et al 2020;).…”