On the Origin of Magnetic Pertubations associated with the FIP effect
Journal
Date Issued
2021
Author(s)
•
•
Baker, D.
•
Valori, G.
•
Jess, D. B.
•
Jafarzadeh, S.
•
Brooks, D. H.
•
•
•
Grant, S. D. T.
•
Long, D. M.
•
Driel-Gesztelyi, L. van
Abstract
In Stangalini et al (2020) and Baker et al. (2020), magnetic oscillations were
detected in the chromosphere of a large sunspot and found to be linked to the
coronal locations where a First Ionization Potential (FIP) effect was observed.
In an attempt to shed light onto the possible excitation mechanisms of these
localized waves, we further investigate the same data by focussing on the
relation between the spatial distribution of the magnetic wave power and the
overall field geometry and plasma parameters obtained from multi-height
spectropolarimetric non-local thermodynamic equilibrium (NLTE) inversions of
IBIS data. We find that, in correspondence with the locations where the
magnetic wave energy is observed at chromospheric heights, the magnetic fields
have smaller scale heights, meaning faster expansions of the field lines, which
ultimately results in stronger vertical density stratification and wave
steepening. In addition, the acoustic spectrum of the oscillations at the
locations where magnetic perturbations are observed is broader than that
observed at other locations, which suggests an additional forcing driver to the
p-modes. Analysis of the photospheric oscillations in the sunspot surroundings
also reveals a broader spectrum in between the two opposite polarities of the
active region (the leading spot and the trailing opposite polarity plage), and
on the same side where magnetic perturbations are observed in the umbra. We
suggest that strong photospheric perturbations in between the two polarities
are responsible for this broader spectrum of oscillations, with respect to the
p-mode spectrum, resulting in locally-excited acoustic waves that, after
crossing the equipartition layer, located close to the umbra-penumbra boundary
at photopheric heights, are converted into magnetic-like waves and steepen due
to the strong density gradient.
Volume
656
Start page
A87
Issn Identifier
0004-6361
Rights
open.access
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