Recently, Astronomy & Astrophysics published an article performed by Professor SHEN Yuandeng and his co-authors from Yunnan Observatories by using multi-wavelength observations taken by the Solar and Heliospheric Observatory (SOHO) and the Solar Dynamic Observatory (SDO). The study presented the first observation of an interesting quasi-periodic fast-propagating (QFP) wave train along open magnetic field lines in the outer corona at a height of about 2 to 4 solar radii in the white-light images taken by the Large Angle Spectroscopic Coronagraph (LASCO) on board the SOHO.

QFP wave trains are usually observed in the low corona using extreme ultraviolet images, and can be divided into two categories including narrow and broad QFP wave trains propagating along and perpendicular to magnetic field, respectively. Both types are tightly associated with periodic pulsations in flares, but their excitation mechanisms are still an open question although some candidate scenarios have been proposed. As suggested in a recent review article written by SHEN et al. 2022, SoPh, 297, 20, QFP wave trains and flare periodic pulsations might manifest two different aspects of the same physical process.

Researchers firstly reported the observation of a QFP wave train in the outer corona at a height range of about 2-4 solar radii by using the white-light images taken by the LASCO instrument on board the SOHO. Meanwhile, they further found a magnetic breakout topology in the low corona eruption source region, which is composed of a large high-lying loop hosting three low-lying loops. Different to typical breakout reconnection which occurs between the middle low-lying and the high-lying large loops, the reconnection occurred between the two sided low-lying loops.

"Such reconnection does not result in a coronal mass ejection in the outer corona, since the reconnection continuously generates new reconnected high-lying large loops so that the confining ability of the high-lying loop becomes more and more strong. Therefore, the eruption in the low corona should be a failed eruption,” said Prof. SHEN. This process also leads to successive stretching and expanding of the newly formed reconnected high-lying loops, which can naturally excite the observed QFP wave train owing to the pulsed increase of outward magnetic and plasma pressures. By using the measured wave parameters, the researchers also derived the magnetic field strength in the outer corona by using the method of coronal seismology.

This observation presents the first white-light imaging observation of QFP wave trains in the outer corona, and provides the detailed energy releasing process in the low corona magnetic reconnection that subsequently excited the observed QFP wave train.

Contact:
SHEN Yuandeng
Yunnan Observatories, CAS
Email: ydshen@ynao.ac.cn