On the surface structure of sunspots

TL;DR

This paper investigates the surface structure of sunspots, focusing on velocity and magnetic fields, moat flow, and magnetic polarity signals, using high-resolution observations to improve helioseismic models.

Contribution

It provides new insights into the velocity and magnetic field configurations in sunspots and explains the hidden opposite polarity signals in magnetograms.

Findings

Penumbral velocity fields quantified at multiple levels

Moat flow around sunspots characterized

Opposite polarity signals are hidden due to limited spectral resolution

Abstract

A precise knowledge of the surface structure of sunspots is essential to construct adequate input models for helioseismic inversion tools. We summarize our recent findings about the velocity and magnetic field in and around sunspots using HINODE observation. To this end we quantize the horizontal and vertical component of the penumbral velocity field at different levels of precision and study the moat flow around sunspot. Furthermore, we find that a significant amount of the penumbral magnetic fields return below the surface within the penumbra. Finally, we explain why the related opposite polarity signals remain hidden in magnetograms constructed from measurements with limited spectral resolution.