Investigating the origin of magnetic perturbations associated with the FIP Effect

Abstract

Recently, 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 on the possible excitation mechanisms of these localized waves, we further investigate the same data by focusing 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, in correspondence with the locations where the magnetic wave energy is observed at chromospheric heights, that 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 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 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 waves and steepen due to the strong density gradient.

Intriguing Plasma Composition Pattern in a Solar Active Region: A Result of Nonresonant Alfvén Waves?

“…Numerical simulations by Dahlburg et al (2016) support the presence of the ponderomotive acceleration in solar coronal loops, with the appropriate magnitude and direction, and suggest it is a "by-product" of coronal heating. Recent work by Baker et al (2021), Murabito et al (2021), and Stangalini et al (2021) found magnetic fluctuations in the chromosphere being magnetically connected to regions of high FIP bias in the corona, which supports this theoretical model. More recent numerical simulations by Réville et al (2021) using a shell turbulence model found that, under the assumption that turbulence is the main driver of coronal heating and solar wind acceleration, a ponderomotive force can appear in the chromosphere and the transition region, and can be strong enough to create the FIP effect.…”

Searching for Evidence of Subchromospheric Magnetic Reconnection on the Sun

“…20 Dopplergram velocities were calibrated taking into account the orbital motion of SDO/HMI and the radial velocity of the Sun using the HMI ring diagrams available from JSOC. The mean Doppler velocity of each map is subtracted from all pixels within the map (Couvidat et al 2016;Murabito et al 2021).…”

Coronal Abundances in an Active Region: Evolution and Underlying Chromospheric and Transition Region Properties

“…In Figure 7, we show an example of these maps from the start of the observing sequences on 2019 April 10, where for the IRIS 2 results we show the map of v turb at τ = −4.2 (typically the inversions are better constrained in the τ range ∼−3.8 to ∼−5). The choice of showing the v turb is motivated by both theoretical and observational results: the fractionation model of Laming (e.g., Laming 2015 and references therein) predicts a dependence of FIP bias on the magnetic waves propagating and/or reflecting in the chromosphere, and recent observations of a sunspot found Alfvénic waves associated with FIP bias enhancements (Baker et al 2021;Murabito et al 2021;Stangalini et al 2021). Assuming all the microturbulence comes from temporal unresolved Álfven waves, the time integration provides an upper limit of the frequencies, and the values of the microturbulence will be associated with the amplitude.…”