Morphology and density of post-CME current sheets

TL;DR

This study investigates the physical characteristics of post-CME rays, supporting the interpretation that they are formed by Petschek-like magnetic reconnection in large-scale current sheets, with measurements aligning with analytical models.

Contribution

It provides observational evidence and analytical modeling that confirm the formation of post-CME rays through Petschek-like reconnection in the coronal current sheet.

Findings

Rays occur as a consequence of Petschek-like reconnection.

Inflow velocities range from 3 to 30 km/s.

Rays have a density an order of magnitude higher than the ambient corona.

Abstract

Eruption of a coronal mass ejection (CME) drags and "opens" the coronal magnetic field, presumably leading to the formation of a large-scale current sheet and the field relaxation by magnetic reconnection. We analyze physical characteristics of ray-like coronal features formed in the aftermath of CMEs, to check if the interpretation of this phenomenon in terms of reconnecting current sheet is consistent with the observations. The study is focused on measurements of the ray width, density excess, and coronal velocity field as a function of the radial distance. The morphology of rays indicates that they occur as a consequence of Petschek-like reconnection in the large scale current sheet formed in the wake of CME. The hypothesis is supported by the flow pattern, often showing outflows along the ray, and sometimes also inflows into the ray. The inferred inflow velocities range from 3 to 30 km s$^{-1}$, consistent with the narrow opening-angle of rays, adding up to a few degrees. The density of rays is an order of magnitude larger than in the ambient corona. The density-excess measurements are compared with the results of the analytical model in which the Petschek-like reconnection geometry is applied to the vertical current sheet, taking into account the decrease of the external coronal density and magnetic field with height. The model results are consistent with the observations, revealing that the main cause of the density excess in rays is a transport of the dense plasma from lower to larger heights by the reconnection outflow.