The Role of Magnetic Fields in Transient Seismic Emission Driven by Atmospheric Heating in Flares

TL;DR

This paper explores how magnetic fields influence seismic emissions during solar flares, suggesting that inclined magnetic fields reduce radiative losses and facilitate energy transfer into the solar interior, explaining observed seismic activity.

Contribution

It highlights the importance of magnetic fields, especially inclined ones, in enabling seismic emissions by reducing radiative losses during flare-induced shocks.

Findings

Inclined magnetic fields increase the chromospheric compressional modulus.

Magnetic fields reduce radiative losses during shock propagation.

Seismic sources are correlated with regions of strong, inclined magnetic fields.

Abstract

The physics of transient seismic emission in flares remains largely mysterious. Its discoverers proposed that these "sunquakes" are the signature of a shock driven by "thick-target heating" of the flaring chromosphere. H-{\alpha} observations show evidence for such a shock. However, simulations of shocks driven by impulsive chromospheric heating show withering radiative losses as the shock proceeds downward. The compression of the shocked gas heats and increases its density, making it more radiative. So, radiative losses increase radically with the strength of the shock. This has introduced doubt that sufficient energy from such a shock can penetrate into the solar interior to match that indicated by the helioseismic signatures. We point out that simulations of acoustic transients driven by impulsive heating have no account for magnetic fields characteristic of transient-seismic-source environments. These must have a major impact on the seismic flux conducted into the solar interior. A strong horizontal magnetic field, for example, greatly increases the compressional modulus of the chromospheric medium. This greatly reduces compression of the gas, hence the radiative losses as the transient passes through it. This could explain the strong affinity of seismic sources to regions of strong, highly inclined penumbral magnetic fields. The role of inclined magnetic fields, then, is fundamental to our understanding of the role of impulsive heating in transient seismic emission.