Are all flare ribbons simply connected to the corona?

TL;DR

This study investigates the connection between flare ribbons and the corona, finding most are linked but some may result from alternative mechanisms like reconnection below the corona.

Contribution

It provides observational evidence that not all flare ribbons are connected to the corona, suggesting multiple mechanisms for flare ribbon formation.

Findings

Most ribbons are connected to the corona

Some ribbons lack clear coronal connection

Reconnection below the corona can explain certain ribbons

Abstract

We consider the observational basis for the belief that flare ribbons in the chromosphere result from energy transport from the overlying corona. We study ribbons of small flares using magnetic as well as intensity data from the Hinode, SDO and IRIS missions. While most ribbons appear connected to the corona, and they over-lie regions of significant vertical magnetic field, we examine one ribbon with no clear evidence for such connections. Evolving horizontal magnetic fields seen with Hinode suggest that reconnection with pre-existing fields below the corona can explain the data. The identification of just one, albeit small, ribbon, with no apparent connection to the corona, leads us to conclude that at least two mechanisms are responsible for the heating that leads to flare ribbon emission.