3D numerical MHD modeling of sunspots with radiation transport

TL;DR

This paper reviews recent 3D radiative MHD simulations of sunspots, focusing on the magnetic and convective processes that produce penumbral structures and the Evershed flow, highlighting the role of Lorentz forces.

Contribution

It presents new insights into the magneto-convective mechanisms driving penumbral outflows using high-resolution 3D simulations, advancing understanding beyond simplified models.

Findings

Horizontal outflows are driven by kinetic energy redistribution along filaments.

Lorentz force primarily facilitates the energy redistribution leading to the Evershed flow.

Strong horizontal magnetic fields are present within penumbral filaments.

Abstract

Sunspot fine structure has been modeled in the past by a combination of idealized magneto-convection simulations and simplified models that prescribe the magnetic field and flow structure to a large degree. Advancement in numerical methods and computing power has enabled recently 3D radiative MHD simulations of entire sunspots with sufficient resolution to address details of umbral dots and penumbral filaments. After a brief review of recent developments we focus on the magneto-convective processes responsible for the complicated magnetic structure of the penumbra and the mechanisms leading to the driving of strong horizontal outflows in the penumbra (Evershed effect). The bulk of energy and mass is transported on scales smaller than the radial extent of the penumbra. Strong horizontal outflows in the sunspot penumbra result from a redistribution of kinetic energy preferring flows along the filaments. This redistribution is facilitated primarily through the Lorentz force, while horizontal pressure gradients play only a minor role. The Evershed flow is strongly magnetized: While we see a strong reduction of the vertical field, the horizontal field component is enhanced within filaments.