The rotation rate of solar active and ephemeral regions -- I. Dependence on morphology and peak magnetic flux

TL;DR

This study measures the rotation rates of solar active and ephemeral regions, revealing size-dependent rotation speeds and differences based on magnetic and morphological classifications, which suggest varying anchoring depths within the solar convection zone.

Contribution

It provides the first comprehensive analysis of how the rotation rates of solar magnetic regions depend on their size, morphology, and magnetic properties, offering insights into their anchoring depths.

Findings

Ephemeral regions rotate faster than active regions.

Unipolar active regions have lower rotation rates.

Rotation rates suggest different anchoring depths within the convection zone.

Abstract

Using magnetic field maps acquired by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory we measured rotation rates of 864 active and 322 ephemeral regions observed between 2010 and 2016. We found smaller magnetic tracers to show a tendency to rotate faster as compared to larger ones. Thus, ephemeral regions exhibit on average the fastest rotation rate. We further divided active regions into three classes. Class A comprised magnetic bipoles obeying Hale's polarity law, Joy's law, and exhibiting more coherent leading polarity in comparison with the following one. The second class B included active regions violating at least one of the aforementioned empirical laws. The third class U comprised unipolar active regions. We found no significant difference between the rotation rates of active regions of classes A and B. In contrast, unipolar active regions exhibited on average lower rotation rate and narrower distribution of the rotation rate differences. Assuming the rotation rate to indicate the anchoring depth of the magnetic structure within the convection zone, we supposed that active regions of classes A and B might be anchored throughout the entire convective envelope while unipolar active regions a rooted within a thin layer located either near the base of the convection zone or at a shallow near-surface depth.