Modelling of asymmetric nanojets in coronal loops

TL;DR

This study investigates how the curvature of coronal loops influences the asymmetry and energy of nanojets resulting from magnetic reconnection, combining analytical and numerical models to explain observed unidirectional jets in the solar corona.

Contribution

It introduces a combined analytical and MHD numerical approach to demonstrate the impact of loop curvature on nanojet asymmetry and energy in coronal reconnection events.

Findings

Inward magnetic tension is significantly stronger than outward tension.

Large retracting lengths can suppress outward jets.

Inward jets are more energetic and their asymmetry increases with smaller reconnection angles.

Abstract

Observations of reconnection jets in the solar corona are emerging as a possible diagnostic to study highly elusive coronal heating. Such nanojets can be observed in coronal loops and they have been linked to nanoflares. However, while models successfully describe the bilateral post-reconnection magnetic slingshot effect that leads to the jets, observations reveal that nanojets are unidirectional, or highly asymmetric, with only the jet travelling inward with respect to the coronal loop's curvature being clearly observed. The aim of this work is to address the role of the curvature of the coronal loop in asymmetric reconnection jets. In order to do so, we first use a simplified analytical model where we estimate the post-reconnection tension forces based on the local intersection angle between the pre-reconnection magnetic field lines and on their post-reconnection retracting length towards new equilibria. Second, we use a simplified numerical magnetohydrodynamic (MHD) model to study how two opposite propagating jets evolve in curved magnetic field lines. Our analytical model demonstrates that in the post-reconnection reorganised magnetic field, the inward directed magnetic tension is inherently stronger (up to 3 orders of magnitude) than the outward directed one and that, with a large enough retracting length, a regime exists where the outward directed tension disappears, leading to no outward jet at large, observable scales. Our MHD numerical model provides support for these results proving also that in the following time evolution the inward jets are consistently more energetic. The degree of asymmetry is also found to increase for small-angle reconnection and for more localised reconnection regions. This work shows that the curvature of the coronal loops plays a role in the asymmetry of the reconnection jets and inward directed jets are more likely to occur and more energetic.