Transverse Wave-Induced Kelvin-Helmholtz Rolls in Spicules
Monday
Abstract details
id
Transverse Wave-Induced Kelvin-Helmholtz Rolls in Spicules
Date Submitted
2019-03-13 22:20:15
Patrick
Antolin
University of St Andrews
Magnetohydrodynamic Waves and Instabilities in the Solar Atmosphere in the High-Resolution Era
Talk
P. Antolin (University of St Andrews), D. Schmit (Catholic University), T. M. D. Pereira (University of Oslo), B. De Pontieu (LMSAL), I. De Moortel (University of St Andrews)
In addition to their jet-like dynamic behavior, spicules usually exhibit strong transverse speeds, multi-stranded structure, and heating from chromospheric to transition region temperatures. In this work we first analyze Hinode and IRIS observations of spicules and find different behaviors in terms of their Doppler velocity evolution and collective motion of their sub-structure. Some have a Doppler shift sign change that is rather fixed along the spicule axis, and lack coherence in the oscillatory motion of strand-like structure, matching rotation models, or long- wavelength torsional Alfvén waves. Others exhibit a Doppler shift sign change at maximum displacement and coherent motion of their strands, suggesting a collective MHD wave. By comparing with an idealized 3D MHD simulation combined with radiative transfer modeling, we analyze the role of transverse MHD waves and associated instabilities in spicule-like features. We find that transverse wave induced Kelvin–Helmholtz (TWIKH) rolls lead to coherence of strand-like structure in imaging and spectral maps, matching some observations. The rapid transverse dynamics and the density and temperature gradients at the spicule boundary lead to Mg II k and Ca II H source functions maxima at the boundary, potentially allowing IRIS to capture the KHI dynamics. Twists and currents propagate along the spicule at Alfvénic speeds, and the temperature variations within TWIKH rolls, produce the sudden appearance/disappearance of strands seen in Doppler velocity and in Ca II H intensity. However, only a mild intensity increase in higher-temperature lines is obtained, suggesting there is an additional heating mechanism at work in spicules.
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