Turbulence and Heating in the Side and Wake Regions of Coronal Mass Ejection in the Low Corona

Abstract:

Ahead of CMEs usually exist the shocked sheaths, in which the background solar corona / solar wind is heated due to the compression of the driving CME. The other regions around the CME, e.g., the side and wake, which may also be influenced by the CME, are the objects of this work. Various instruments including LASCO, AIA, and CoMP observed a CME close to the east limb on October 26th, 2013. The CME core is very hot (~10 MK) (appearing only in the 131 channel of AIA), and ejects away at a high speed (~330 km/s). Magnetic structures (low-lying loops and large loop legs) on both sides and in the wake of the CME are strongly disturbed, showing turbulent signatures with enhanced Doppler-shift oscillations (~±15km/s) and effective thermal velocities (~60 km/s) from the CoMP observations in the Fe XIII line. As recognized from the CoMP Doppler-shift maps, the turbulent vortices behave differently at various heights, illustrating torsional oscillations back and forth around the leg axis at lower altitude and continuous rotation with the same handedness at higher altitude. This difference may be due to the lower part being more likely to be line-tied with the motionless footpoint than the upper part. The turbulence of loop legs is also revealed in the AIA animations in the Fe 171 Å and Fe 193 Å channels with some differences between each other. The turbulence in Fe 171 Å seems to be weaker than that in Fe 193 Å, with the former behaving more wave-like and the latter involving more whirling vortices. The difference in turbulence level might come from the difference in turnover time of the vortices: ~1000s for Fe 171 Å and ~500s for Fe 193 Å. Moreover, in the wake of the CME, the eddies turning over up and down as well as the eddies rotating horizontally are also presented in the Fe 193 Å. The leg-like straps in Fe 171 Å seem to be braided by the turbulent vortices, and disappear afterwards probably due to heating by coherent current sheet formed between braided straps. Meanwhile, low-lying loops are oscillating back and forth during its reaction to the fast compressive waves as driven by the CME. The subsequent brightening of the low-lying loops implies a heating due to the dissipation of compressive waves. This work suggests that the effects at the side and wake of the CME cannot be ignored when considering the heating of the solar corona and solar wind.