Analysis of a coronal hole jet in the chromosphere and the transition region with IRIS and SDO observations

Coronal jets are transient phenomena that occur throughout the solar atmosphere, and they are often triggered by the activation of mini-filaments. Jets are an important subject to study, as they are believed to contribute to the mass supply of the solar wind. We studied a small-scale solar jet occurring in a low-latitude coronal hole, utilizing chromospheric and transition region diagnostics to investigate traces of the jet eruption in the lower atmosphere. We also investigate the possible mechanisms and dynamic conditions leading to its onset. We analyzed ultraviolet spectra from the Interface Region Imaging Spectrograph (IRIS) to investigate chromospheric dynamics and their connection to the transition region, using diagnostics of the Mg k 2796.35 Å and Si ii iv 1393.75 Å lines together with non- local thermodynamic equilibrium inversions. We complemented this analysis with multiwavelength imaging and magnetograms from the Solar Dynamics Observatory (SDO) as well as magnetic field modeling. Our analysis of the Mg k and Si parameters revealed a coupling between chromospheric and transition region plasma dynamics. Profiles on the jet spire present deeper central reversals, larger peak separations, and higher transition region Doppler velocities. The jet initiation is associated with a mini-filament-like structure, which is preceded by dynamic variations in the photospheric magnetic field. We find single-peaked Mg k profiles at one of its footpoints, possibly indicating plasma drainage. The presence of a null point and a quasi-separatrix layer suggests that reconnection can play a role in the mini-filament-like structure destabilization and jet eruption. ii iv ii This study suggests that the signature and possibly the origin of coronal jets can be traced down to the chromosphere. The detailed analysis of the Mg k profiles at the jet spire and the mini-filament-like structure may provide valuable observational constraints for future magnetohydrodynamic (MHD) simulations. ii