Is magnetic reconnection the cause of supersonic upflows in granular cells ?

TL;DR

This study investigates the physical mechanisms behind supersonic magnetic upflows in solar granular cells, finding evidence that magnetic reconnection may be responsible, though other mechanisms could also contribute.

Contribution

It provides detailed physical parameter analysis of these upflows using advanced inversion techniques, highlighting magnetic reconnection as a potential cause.

Findings

Many events show magnetic polarity reversal and temperature enhancement.

Supersonic line-of-sight velocities are observed in the events.

Magnetic reconnection is a plausible explanation, but not definitive.

Abstract

In a previous work, we reported on the discovery of supersonic magnetic upflows on granular cells in data from the {\sc Sunrise}/IMaX instrument. In the present work we investigate the physical origin of these events employing data of the same instrument but with higher spectral sampling. By means of the inversion of Stokes profiles we are able to recover the physical parameters (temperature, magnetic field, line-of-sight velocity, etc) present in the solar photosphere at the time of these events. The inversion is performed in a Monte-Carlo-like fashion, that is, repeating it many times with different initializations and retaining only the best result. We find that many of the events are characterized by a reversal in the polarity of the magnetic field along the vertical direction in the photosphere, accompanied by an enhancement in the temperature and by supersonic line-of-sight velocities. In about half of the studied events, large blue-shifted and red-shifted line-of-sight velocities coexist above/below each other. These features can be explained in terms of magnetic reconnection, where the energy stored in the magnetic field is released in the form of kinetic and thermal energy when magnetic field lines of opposite polarities coalesce. However, the agreement with magnetic reconnection is not perfect and therefore, other possible physical mechanisms might also play a role.