paper

Magneto-seismological insights into the penumbral chromosphere and evidence for wave damping in spicules

arXiv:1405.3203 · doi:10.1051/0004-6361/201423718

Abstract

The observation of propagating magneto-hydrodynamic kink waves in magnetic structures and measurement of their properties (amplitude, phase speed) can be used to diagnose the plasma conditions in the neighbourhood of the magnetic structure via magneto-seismology (MS). We aim to reveal properties of the chromosphere/Transition Region above the sunspot penumbra using this technique. Hinode observed a sunspot as it was crossing the limb, providing a unique side on view of the sunspot atmosphere. The presence of large spicule-like jets is evident in \ion{Ca}{II} H images. The jets are found to support transverse wave motions that displace the central axis, which can be interpreted as a kink wave. The properties of a wave event are measured and used to determine the magnetic and density stratification along the structure. We also measure the width of the spicule and the intensity profile along the structure. The measured wave properties reveal an initial rapid increase in amplitude with height above the solar surface, followed by a decrease in amplitude. The MS inversion suggests this initial increase corresponds to large changes in density and magnetic field strength. In addition, we provide the first measurements of spicule width with height, which confirm that the spicule under goes rapid expansion. The measured expansion shows good agreement with the results from the MS. The observed variations in plasma parameters are suggested to be partly due to the presence of a gravitational stratified, ambient atmosphere. Combining width measurements with phase speed measurements implies the observed decrease in wave amplitude at greater heights can be explained by wave damping. Hence, we provide the first direct evidence of wave damping in chromospheric spicules and the quality factor of the damping is found to be significantly smaller than estimated coronal values.

13 pages, 10 figures - Accepted in A&A

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