Turbulence: Important Trigger for Coronal Mass Ejection Plasma Heating and Coronal Wave Trains (Planetary Science)

In a study published in The Astrophysical Journal, Dr. YE Jing from Yunnan Observatories of the Chinese Academy of Sciences and his collaborators reported their findings on the erupted flux rope. They analyzed the dynamics and the energy budget of turbulence in the termination region under the coronal mass ejection (CME).

CMEs are the largest explosion in the solar system, where vast amounts of magnetic energy equivalent to billions of H-bombs are released through magnetic reconnection. The CME plasma has been observed to be strongly heated during solar eruptions, but the heating mechanism is not understood yet.

To quantitatively study the hot, dense region at the bottom of the CME, the researchers implemented a high-resolution 2.5D magnetohydrodynamical (MHD) simulation, considering realistic cooling processes.

The results showed that the interaction between the tearing current sheet and the turbulence, including the termination shocks (TSs) at the base of the CME, can make a significant contribution to heating the CME. The cumulative heating rate in this region is computed to be greater than the kinetic energy transfer rate, consistent with the fast blob observed by the Ultraviolet Coronagraph Spectrometer (UVCS) during a CME on June 28, 2000.

Besides, the researchers found that the turbulence is surprisingly somewhat amplified by the TSs. The compression ratio of the TS under the CME can exceed four due to thermal conduction, but such a strong TS is hardly detectable in all Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) bands.

On the other hand, they noticed coronal wave trains at higher altitudes under the CME. It seems that the turbulent region repeatedly forms a downward magnetic tuning fork to generate outward-propagating fast waves. And the turbulence is an important contributor to the periodic generation of the coronal wave trains around.

The hot, dense region just above the upper TS in their simulation has not yet been reported in AIA observations of solar eruptions. However, it may have been detected in UVCS observations of fast CMEs from X-class flares. The 2002 April 21 event in particular showed [Fe XVIII] from a small region apparently near the base of the flux rope.

This study helps to better understand the origin of extreme ultra-violet disturbances observed at the lateral sides of the erupted flux rope.

Reference: Jing Ye, Qiangwei Cai, Chengcai Shen, John C. Raymond, Zhixing Mei, Yan Li, and Jun Lin, “Coronal Wave Trains and Plasma Heating Triggered by Turbulence in the Wake of a CME”, The Astrophysical Journal, Volume 909, Number 1, 2021. https://iopscience.iop.org/article/10.3847/1538-4357/abdeb5

Provided by Chinese Academy of Sciences

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