A topology for the penumbral magnetic fields

TL;DR

This paper proposes a magnetic field topology model for sunspot penumbrae involving short magnetic loops that explain observed flows and filament structures, aligning with recent observations and theoretical expectations.

Contribution

It introduces a novel scenario with short magnetic loops filling penumbrae, explaining flows and filament dark cores, and suggests observational tests for validation.

Findings

Consistent with observed dark-cored filaments

Explains Evershed flows via magnetic loops

Predicts increased velocities with better resolution

Abstract

We describe a scenario for the sunspot magnetic field topology that may account for recent observations of upflows and downflows in penumbrae. According to our conjecture, short narrow magnetic loops fill the penumbral volume. Flows along these field lines are responsible for both the Evershed effect and the convective transport. This scenario seems to be qualitatively consistent with most existing observations, including the dark cores in penumbral filaments reported by Scharmer et al. Each bright filament with dark core would be a system of two paired convective rolls with the dark core tracing the lane where the plasma sinks down. The magnetic loops would have a hot footpoint in one of the bright filament and a cold footpoint in the dark core. The scenario also fits in most of our theoretical prejudices (siphon flows along field lines, presence of overturning convection, drag of field lines by downdrafts, etc). If the conjecture turns out to be correct, the mild upward and downward velocities observed in penumbrae must increase upon improvement of the current spatial resolution. This and other observational tests to support or disprove the proposed scenario are put forward.