Models and Observations of Sunspot Penumbrae

TL;DR

This paper reviews current models of sunspot penumbrae, discusses their limitations with recent high-resolution observations, and proposes modifications to unify them into a comprehensive framework supported by recent simulations.

Contribution

It critically evaluates two leading models of sunspot penumbrae, highlights their shortcomings, and suggests modifications to reconcile them with recent high-resolution data and simulations.

Findings

Current models have limitations explaining recent high-resolution observations.

Proposed modifications unify the models into a coherent picture.

The unified model aligns well with recent 3D MHD simulations.

Abstract

The mysteries of sunspot penumbrae have been under an intense scrutiny for the past 10 years. During this time, some models have been proposed and refuted, while the surviving ones had to be modified, adapted and evolved to explain the ever-increasing array of observational constraints. In this contribution I will review two of the present models, emphasizing their contributions to this field, but also pinpointing some of their inadequacies to explain a number of recent observations at very high spatial resolution. To help explaining these new observations I propose some modifications to each of them. These modifications bring those two seemingly opposite models closer together into a general picture that agrees well with recent 3D magneto-hydrodynamic simulations.