A rising cool column as signature for helical flux emergence and formation of prominence and coronal cavity

TL;DR

This study observes a rising cool plasma column associated with a coronal cavity, interpreting it as evidence of helical flux emergence and reconnection, which influences prominence formation and coronal dynamics.

Contribution

It provides the first detailed observation linking a rising cool column to helical flux emergence and reconnection processes in the solar corona.

Findings

A cool plasma column rises at 2 km/s with fine structures moving up to 20 km/s.

The coronal cavity moves upward at about 5 km/s during the event.

The observations support the emergence of a helical flux rope causing prominence and cavity dynamics.

Abstract

Continuous observations were performed of a quiescent prominence with the Solar Optical Telescope (SOT) on board the /emph{Hinode} satellite on 2006 December 23--24. A peculiar slowly-rising column of $/sim10^{4}$ K plasma develops from the lower atmosphere during the observations. The apparent ascent speed of the column is 2 km s$^{-1}$, while the fine structures of the column exhibit much faster motion of up to 20 km s$^{-1}$. The column eventually becomes a faint low-lying prominence. Associated with the appearance of the column, an overlying coronal cavity seen in the X-ray and EUV moves upward at $/sim$5 km s$^{-1}$. We discuss the relationship between these episodes, and suggest that they are due to the emergence of a helical flux rope that undergoes reconnection with lower coronal fields, possibly carrying material into the coronal cavity. Under the assumption of the emerging flux scenario, the lower velocity of 2 km s$^{-1}$ and the higher one of 20 km s$^{-1}$ in the column are attributed to the rising motion of the emerging flux and to the outflow driven by magnetic reconnection between the emerging flux and the pre-existing coronal field, respectively. The present paper gives a coherent explanation of the enigmatic phenomenon of the rising column with the emergence of the helical rope, and its effect on the corona. We discuss the implications that the emergence of such a helical rope has on the dynamo process in the convection zone.