Granular-Scale Elementary Flux Emergence Episodes in a Solar Active Region

TL;DR

This study investigates small-scale flux emergence in a solar active region, revealing elementary flux emergence episodes characterized by short-lived dark features, associated brightenings, and magnetic reconnection, advancing understanding of serpentine flux emergence.

Contribution

The paper presents detailed observations of granular-scale flux emergence events, providing new insights into the dynamics and signatures of elementary flux emergence in the solar atmosphere.

Findings

Detection of short-lived dark features in Ca II H and Stokes I images.

Observation of diverging bipolar magnetic configurations during emergence.

Identification of chromospheric brightenings linked to magnetic reconnection.

Abstract

We analyze data from Hinode spacecraft taken over two 54-minute periods during the emergence of AR 11024. We focus on small-scale portions within the observed solar active region and discover the appearance of very distinctive small-scale and short-lived dark features in Ca II H chromospheric filtergrams and Stokes I images. The features appear in regions with close-to-zero longitudinal magnetic field, and are observed to increase in length before they eventually disappear. Energy release in the low chromospheric line is detected while the dark features are fading. In time series of magnetograms a diverging bipolar configuration is observed accompanying the appearance of the dark features and the brightenings. The observed phenomena are explained as evidencing elementary flux emergence in the solar atmosphere, i.e small-scale arch filament systems rising up from the photosphere to the lower chromosphere with a length scale of a few solar granules. Brightenings are explained as being the signatures of chromospheric heating triggered by reconnection of the rising loops (once they reached chromospheric heights) with pre-existing magnetic fields as well as to reconnection/cancellation events in U-loop segments of emerging serpentine fields. We study the temporal evolution and dynamics of the events and compare them with the emergence of magnetic loops detected in quiet sun regions and serpentine flux emergence signatures in active regions. Incorporating the novel features of granular-scale flux emergence presented in this study we advance the scenario for serpentine flux emergence.