First magnetic seismology of the CME reconnection outflow layer in the low corona with 2.5-D MHD simulations of the Kelvin-Helmholtz instability

摘要

For conditions observed in the low corona, we perform 2.5-D magnetohydrodynamic (MHD) simulations of the Kelvin-Helmholtz instability (KHI) at the surface of a coronal mass ejection (CME). We match the observed time development of the KHI with simulated growth from 110 MHD experiments representing a parametric range of realistic magnetic field strengths and orientations and two key values of the velocity shear, ΔV, inferred from observations. The results are field strengths B_e≈ 8-9 G and B _s≈ 10-11 G in the CME reconnection outflow layer and the surrounding sheath, respectively, for ΔV≈770kms~(-1); for nearly perpendicular orientation (1° tilt) of B_s with respect to the flow plane, B_e can be tilted between 3 and 10°; tilting B_s up to 15° would slow the growth of the KHI by too much. Our simulations also reveal hidden dynamics and structure of the CME ejecta layer such as plasma mixing via reconnection in the vortices. Key Points Magnetic field is determined for the first time in the CME ejecta and sheath Magnetic field of the CME ejecta (sheath) can be 8-9 G (10-11 G) The KHI and associated plasma mixing may impact CME geo-effectiveness.