Data-constrained 3D magnetohydrodynamics simulation of a spiral jet caused by an unstable flux rope embedded in a fan–spine configuration

Spiral jets are impulsive plasma ejections that typically show an apparent rotational motion. Their generation, however, is still not understood thoroughly. Based on a high-resolution vector magnetogram from the Polarimetric and Helioseismic Imager on board Solar Orbiter, we constructed a data-constrained three-dimensional (3D) magnetohydrodynamics (MHD) model, aiming to disclose the eruption mechanism of a tiny spiral jet at a moss region observed on March 3, 2022. The initial configuration of the simulation consists of an extrapolated coronal magnetic field based on the vector magnetogram and an inserted unstable flux rope constructed by the regularized Biot-Savart laws method. Our results highlight the critical role of the fan-spine configuration in forming the spiral jet, and confirm the collapse of the pre-existing magnetic null to a curved 3D current sheet where external reconnection takes places. It is further disclosed that the flux rope quickly moves upward, reconnecting with the field lines near the outer spine, thereby enabling the transfer of twisting and cool material from the flux rope to the open field, giving rise to the tiny spiral jet we observed. The notable similarities between these characteristics and those for larger-scale jets suggest that spiral jets, regardless of their scale, essentially share the same eruption mechanism.