Investigating explosive events in a 3D quiet-Sun model: Transition region and coronal response

TL;DR

This study uses a 3D quiet-Sun model to analyze explosive events, revealing how magnetic reconnection and local conditions influence whether these events reach coronal temperatures or remain cool.

Contribution

It provides the first detailed analysis of the magnetic and thermal evolution of explosive events in a realistic 3D quiet-Sun model, linking magnetic reconnection types to temperature outcomes.

Findings

Most explosive events do not reach coronal temperatures.

Hot events are associated with higher magnetic field strength and lower density.

Cool events often involve component reconnection or flux rope relaxation.

Abstract

Transition region explosive events are characterized by non-Gaussian profiles of the emission lines formed at transition region temperatures, and they are believed to be manifestations of small-scale reconnection events in the transition region. We took a 3D self-consistent quiet-Sun model extending from the upper convection zone to the lower corona calculated using the MURaM code. We first synthesized the Si IV line profiles from the model and then located the profiles which show signatures of bi-directional flows. These tend to appear along network lanes, and most do not reach coronal temperatures. We isolated two hot (around 1 MK) events and one cool (order of 0.1 MK) event and examined the magnetic field evolution in and around these selected events. Furthermore, we investigated why some explosive events reach coronal temperatures while most remain cool. The field lines around two events reconnect at small angles, i.e., they undergo component reconnection. The third case is associated with the relaxation of a highly twisted flux rope. All of the three events reveal signatures in the synthesized EUI 174 {\AA} images. The intensity variations in two events are dominated by variations of the coronal emissions, while the cool component seen in the respective channel contributes significantly to the intensity variation in one case. Comparing to the cool event, one hot event is embedded in regions with higher magnetic field strength and heating rates while the densities are comparable, and the other hot event is heated to coronal temperatures mainly because of the low density. Small-scale heating events seen in EUV channels of AIA or EUI might be hot or cool. Our results imply that the major difference between the events in which coronal counterparts dominate or not is the amount of converted magnetic energy and/or density in and around the reconnection region.