Simulation of a Solar Jet Formed from an Untwisting Flux Rope Interacting with a Null Point

Abstract

Coronal jets are eruptions identified by a collimated, sometimes twisted spire. They are small-scale energetic events compared with flares. Using multiwavelength observations from the Solar Dynamics Observatory/Atmospheric Imaging Assembly and a magnetogram from Hinode/Spectro-Polarimeter (Hinode/SP), we study the formation and evolution of a jet occurring on 2019 March 22 in NOAA Active Region 12736. A zero-β magnetohydrodynamic simulation is conducted to probe the initiation mechanisms and appearance of helical motion during this jet event. As the simulation reveals, there are two pairs of field lines at the jet base, indicating two distinct magnetic structures. One structure outlines a flux rope lying low above the photosphere in the north of a bald patch region, and the other structure shows a null point high in the corona in the south. The untwisting motions of the observed flux rope were recovered by adding an anomalous (artificial) resistivity in the simulation. A reconnection occurs at the bald patch in the flux rope structure, which is moving upward and simultaneously encounters the field lines of the null point structure. The interaction of the two structures results in the jet, while the twist of the flux rope is transferred to the jet by the reconnected field lines. The rotational motion of the flux rope is proposed to be an underlying trigger of this process and responsible for helical motions in the jet spire.