The pre-penumbral magnetic canopy in the solar atmosphere

TL;DR

This paper investigates the formation of magnetic canopies in the solar atmosphere, proposing that they result from magnetic flux emergence and are crucial for penumbra development, supported by simulations of twisted flux tube emergence.

Contribution

It demonstrates through simulations that highly inclined magnetic canopies form during flux emergence, explaining penumbra formation in sunspots.

Findings

Magnetic canopies form preferentially at specific locations during flux emergence.

Simulations support the idea that canopies are a consequence of magnetic flux emergence.

Canopies act as progenitors for penumbrae in sunspots.

Abstract

Penumbrae are the manifestation of magnetoconvection in highly inclined (to the vertical direction) magnetic field. The penumbra of a sunspot tends to form, initially, along the arc of the umbra antipodal to the main region of flux emergence. The question of how highly inclined magnetic field can concentrate along the antipodal curves of umbrae, at least initially, remains to be answered. Previous observational studies have suggested the existence of some form of overlying magnetic canopy which acts as the progenitor for penumbrae. We propose that such overlying magnetic canopies are a consequence of how the magnetic field emerges into the atmosphere and are, therefore, part of the emerging region. We show, through simulations of twisted flux tube emergence, that canopies of highly inclined magnetic field form preferentially at the required locations above the photosphere.