Coronal jets are eruptions identified by a collimated, sometimes twisted
spire. They are small-scale energetic events compared with flares. Using
multi-wavelength observations from the Solar Dynamics Observatory/Atmospheric
Imaging Assembly (SDO/AIA) and a magnetogram from Hinode/Spectro-Polarimeter
(Hinode/SP), we study the formation and evolution of a jet occurring on 2019
March 22 in the active region NOAA 12736. A zero-β magnetohydrodynamic
(MHD) 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 was 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 upwards 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.Comment: 17pages, 9 figures. Accepted for publication in The Astrophysical
Journa