The solar internetwork. III. Unipolar versus bipolar flux appearance

TL;DR

This study analyzes small-scale internetwork magnetic fields on the Sun, revealing two distinct types—unipolar and bipolar—with bipolar features emerging faster and contributing more to the overall magnetic flux.

Contribution

It distinguishes between unipolar and bipolar flux emergence modes and links bipolar features to new flux emergence, using high-resolution observations and simulations.

Findings

Bipolar features are larger, stronger, and longer-lived than unipolar features.

Bipolar features account for about 70% of the total IN flux.

Bipolar flux emerges faster than unipolar flux.

Abstract

Small-scale internetwork (IN) magnetic fields are considered to be the main building blocks of the quiet Sun magnetism. For this reason, it is crucial to understand how they appear on the solar surface. Here, we employ a high-resolution, high-sensitivity, long-duration Hinode/NFI magnetogram sequence to analyze the appearance modes and spatio-temporal evolution of individual IN magnetic elements inside a supergranular cell at the disk center. From identification of flux patches and magnetofrictional simulations, we show that there are two distinct populations of IN flux concentrations: unipolar and bipolar features. Bipolar features tend to be bigger and stronger than unipolar features. They also live longer and carry more flux per feature. Both types of flux concentrations appear uniformly over the solar surface. However, we argue that bipolar features truly represent the emergence of new flux on the solar surface, while unipolar features seem to be formed by coalescence of background flux. Magnetic bipoles appear at a faster rate than unipolar features (68 as opposed to 55 Mx cm$^{-2}$ day$^{-1}$), and provide about 70% of the total instantaneous IN flux detected in the interior of the supergranule.