Kelvin-Helmholtz instability on coronal mass ejecta in the lower corona

Abstract

We model an imaged Kelvin-Helmholtz (KH) instability on a coronal mass ejecta (CME) in the lower corona by investigating conditions under which kink ($m=1$) and $m=-3$ magnetohydrodynamic (MHD) modes in an uniformly twisted flux tube moving along its axis become unstable. We employ the dispersion relations of MHD modes derived from the linearised magnetohydrodynamic equations. We assume real wave numbers and complex angular wave frequencies, namely complex wave phase velocities. The dispersion relations are solved numerically at fixed input parameters (taken from observational data) and various mass flow velocities. It is shown that the stability of the modes depends upon four parameters, the density contrast between the flux tube and its environment, the ratio of the background magnetic fields in the two media, the twist of the magnetic field lines inside the tube, and the value of the Alfvén Mach number (the ratio of the tube velocity to Alfvén speed inside the flux tube). For a twisted magnetic flux tube at a density contrast of $0.88$, background magnetic field ratio of $1.58$, and a normalised magnetic field twist of $0.2$, the critical speed for the kink ($m=-3$) mode (where $m$ is the azimuthal mode number) is $678$ km\,s${}^{-1}$ just as it is observed. The growth rate for this harmonic at KH wavelength of $18.5$ Mm and ejecta width of $4.1$ Mm is equal to $0.037$ s${}^{-1}$, in agreement with observations. KH instability of the $m=-3$ mode may also explain why the KH vortices are seen only at the one side of arising CME. The good agreement between observational and computational data shows that the imaged KH instability on CME can be explained in terms of emerging KH instability of the $m=-3$ MHD mode in twisted magnetic flux tube moving along its axis.

arXiv comment7 pages, 5 figures. arXiv admin note: substantial text overlap with arXiv:1411.6472

References in corpus (13)

• Confined and ejective eruptions of kink-unstable flux ropes
• Solar filament eruptions and their physical role in triggering Coronal Mass Ejections
• A solar tornado observed by AIA/SDO: Rotational flow and evolution of magnetic helicity in a prominence and cavity
• Observation of kink instability during small B5.0 solar flare on 04 June, 2007
• SDO/AIA Observation of Kelvin-Helmholtz Instability in the Solar Corona
• Homologous Flares and Magnetic Field Topology in Active Region NOAA 10501 on 20 November 2003
• Initiation of CME and Associated Flare Caused by Helical Kink Instability Observed by SDO/AIA
• Ubiquitous rotating network magnetic fields and EUV cyclones in the quiet Sun
• The Kelvin-Helmholtz Instability at CME-Boundaries in the Solar Corona: Observations and 2.5D MHD Simulations
• Kelvin-Helmholtz instability of twisted magnetic flux tubes in the solar wind
• A Study of Fast Flareless Coronal Mass Ejections
• Kelvin-Helmholtz instability of kink waves in photospheric twisted flux tubes
• Twisted magnetic flux tubes in the solar wind

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