A recent breakthrough in solar outburst research has been made by a team led by Prof. Gou Yanyu from the University of Science and Technology of China (USTC), part of the Chinese Academy of Sciences (CAS). The team’s findings, published in Nature Astronomy, highlight the intricate evolution of the solar outburst structure during its early stages, representing a significant advancement in this field of study.
In traditional images, the core structure of a solar eruption appears as a magnetic rope comprising coiled magnetic lines. As the eruption commences, the magnetic ropes surrounding the core undergo a process called magnetic reconnection, transforming them into spirally wound magnetic lines that wrap around the original core. This leads to the rapid expansion of the eruption in a “snowball” fashion. However, it was observed that only about one-third of the solar ejecta detected by spacecraft near Earth and in interplanetary space exhibited the expected magnetic structure, while the rest showed substantial deviations from the classical images.
By examining a specific coronal mass ejection event, the researchers uncovered a complex sequence of stripping, disintegration, and reconstruction of the pre-emergence magnetic rope structure during the outburst. Observational evidence indicated that the pre-eruption S-shaped magnetic rope structure originated from small-scale “seeds.”
At the beginning of the outburst, the footpoints of the magnetic ropes are clearly defined by a trapezoidal bright band in the lower atmosphere. As the violent outburst progresses, the footpoints of the outburst structure manifest as darkened regions in the corona due to the absence of material.
Due to the dynamic changes in the solar chromospheric flare band and the subsequent displacement of the coronal darkening region, the footpoints of the eruptive structure undergo significant shifts and barely intersect with the footpoints of the original magnetic rope. This contrasts with the predictions made by classical images, which suggested that the coronal darkening region associated with the footpoints of the eruptive structure should cover the footpoints of the initial magnetic rope.
The end of the flare zone exhibits an irregular pattern and a back-and-forth sawing motion, unveiling the intricate three-dimensional magnetic reconnection occurring within the magnetic rope and between the rope and the surrounding magnetic field. These phenomena indicate that three-dimensional magnetic field reconnection during the eruption almost entirely replaces the magnetic flux of the original magnetic rope.
This study provides a detailed understanding of the process of complex three-dimensional magnetic reconnection and its crucial role in the formation of coronal mass ejections. It offers a new physical explanation for the generation of intricate ejection structures in interplanetary space and contributes to advancements in space weather forecasting.
Source: Chinese Academy of Sciences