Magnetic Flux Loss and Flux Transport in a Decaying Active Region

TL;DR

This study investigates how magnetic flux decreases in a decaying active region by analyzing vector magnetic fields, revealing that flux is transported outward and canceled at the moat boundary, shedding light on flux removal processes.

Contribution

It provides observational evidence linking flux transport and cancellation in a decaying sunspot's moat region using high-resolution spectropolarimetric data.

Findings

Magnetic flux decreases in the sunspot and moat region are balanced by flux transported outward.

Flux loss rates of positive and negative polarities are balanced around the moat boundary.

Most magnetic flux is transported outward and canceled at the moat boundary.

Abstract

We estimate the temporal change of magnetic flux perpendicular to the solar surface in a decaying active region by using a time series of the spatial distribution of vector magnetic fields in the photosphere. The vector magnetic fields are derived from full spectropolarimetric measurements with the Solar Optical Telescope aboard Hinode. We compare a magnetic flux loss rate to a flux transport rate in a decaying sunspot and its surrounding moat region. The amount of magnetic flux that decreases in the sunspot and moat region is very similar to magnetic flux transported to the outer boundary of the moat region. The flux loss rates [$(dF/dt)_{loss}$] of magnetic elements with positive and negative polarities are balanced each other around the outer boundary of the moat region. These results suggest that most of the magnetic flux in the sunspot is transported to the outer boundary of the moat region as moving magnetic features, and then removed from the photosphere by flux cancellation around the outer boundary of the moat region.