Penumbral structure and outflows in simulated sunspots

TL;DR

This paper uses numerical simulations to show that penumbral outflows in sunspots form when magnetic fields are inclined more than 45 degrees, linking magnetic structure to flow patterns.

Contribution

The study demonstrates that penumbral outflows arise from anisotropic convection in inclined magnetic fields exceeding 45 degrees, providing a physical explanation for observed sunspot flows.

Findings

Penumbral outflows form when magnetic inclination exceeds 45 degrees.

Outflows are part of convective energy transport influenced by magnetic anisotropy.

Simulations replicate observed systematic outward flows in sunspot penumbrae.

Abstract

Sunspots are concentrations of magnetic field on the visible solar surface that strongly affect the convective energy transport in their interior and surroundings. The filamentary outer regions (penumbrae) of sunspots show systematic radial outward flows along channels of nearly horizontal magnetic field. These flows were discovered 100 years ago and are present in all fully developed sunspots. Using a comprehensive numerical simulation of a sunspot pair, we show that penumbral structures with such outflows form when the average magnetic field inclination to the vertical exceeds about 45 degrees. The systematic outflows are a component of the convective flows that provide the upward energy transport and result from anisotropy introduced by the presence of the inclined magnetic field.