Solar coronal magnetic fields derived using seismology techniques applied to omnipresent sunspot waves

TL;DR

This paper introduces a novel seismology-based method to map the magnetic field in the solar corona using omnipresent sunspot waves, overcoming limitations of traditional observational techniques.

Contribution

It demonstrates for the first time how sunspot oscillations can be used to precisely map coronal magnetic fields, providing a new tool for solar magnetic studies.

Findings

Coronal magnetic field strength of 32 +/- 5 G above sunspots.

Magnetic field decreases to about 1 G over 7000 km.

New technique offers high-precision magnetic mapping near sunspots.

Abstract

Sunspots on the surface of the Sun are the observational signatures of intense manifestations of tightly packed magnetic field lines, with near-vertical field strengths exceeding 6,000 G in extreme cases. It is well accepted that both the plasma density and the magnitude of the magnetic field strength decrease rapidly away from the solar surface, making high-cadence coronal measurements through traditional Zeeman and Hanle effects difficult since the observational signatures are fraught with low-amplitude signals that can become swamped with instrumental noise. Magneto-hydrodynamic (MHD) techniques have previously been applied to coronal structures, with single and spatially isolated magnetic field strengths estimated as 9-55 G. A drawback with previous MHD approaches is that they rely on particular wave modes alongside the detectability of harmonic overtones. Here we show, for the first time, how omnipresent magneto-acoustic waves, originating from within the underlying sunspot and propagating radially outwards, allow the spatial variation of the local coronal magnetic field to be mapped with high precision. We find coronal magnetic field strengths of 32 +/- 5 G above the sunspot, which decrease rapidly to values of approximately 1 G over a lateral distance of 7000 km, consistent with previous isolated and unresolved estimations. Our results demonstrate a new, powerful technique that harnesses the omnipresent nature of sunspot oscillations to provide magnetic field mapping capabilities close to a magnetic source in the solar corona.