The electrical current density vector in the inner penumbra of a Sunspot

TL;DR

This study maps the full 3D electrical current density in a sunspot's inner penumbra, revealing dominant horizontal currents and detailed magnetic and plasma properties, advancing understanding of sunspot magnetic structures.

Contribution

It provides the first comprehensive 3D vector map of electrical currents in a sunspot penumbra, highlighting the significance of horizontal currents often overlooked in previous studies.

Findings

Horizontal current density is 3-4 times larger than vertical.

Magnetic field and current vectors form about 20-degree angle.

Plasma beta varies significantly with depth and location.

Abstract

We determine the entire electrical current density vector in a geometrical 3D volume of the inner penumbra of a sunspot from an inversion of spectropolarimetric data obtained with Hinode/SP. Significant currents are seen to wrap around the hotter, more elevated regions with lower and more horizontal magnetic field that harbor strong upflows and radial outflows (the intraspines). The horizontal component of the current density vector is 3-4 times larger than the vertical; nearly all previous studies only obtain the vertical component and thus strongly underestimate the current density. The current density and the magnetic field vectors form an angle of about 20 degrees. The plasma beta at the 0 km level is larger than 1 in the intraspines and is one order of magnitude lower in the background component of the penumbra (spines). At the 200 km level, the plasma beta is below 0.3 nearly everywhere. The plasma beta surface as well as the surface optical depth unity are very corrugated. At the borders of intraspines and inside, the magnetic field is not force-free at deeper layers and nearly force free at the top layers. The magnetic field of the spines is close to being potential everywhere. The dissipated ohmic energy is five orders of magnitudes smaller than the solar energy flux and thus negligible for the energy balance of the penumbra.