Impulsive origin of solar spicule-like jets

Using the observations of the coronal hole in Si IV 1393.755 Å line as recorded by interface region imaging spectrograph (IRIS) on 8th October 2013, Chen et al. (Astrophys. J. 873(1):79, 2019) have reported non-Gaussian line profiles showing unusual line broadening that may correspond to the velocity enhancement in the emitting plasma. This observational scenario may be caused by the localized impulsive energy release associated with the footpoint of spicule-like cool jet. We revisit the observations of Chen et al. (Astrophys. J. 873(1):79, 2019) to analyse a specific event showing non-Gaussian profiles in the Si IV 1393.755 Å line, for a lifetime of 3.0 min and Doppler shifts reaching 68 km s ^-1 , which is associated with a spicule-like jet of length 8.0 Mm. We model this jet by implementing an observed velocity enhancement in a magnetized, gravitationally stratified, two-dimensional (2-D) model solar atmosphere. The model atmosphere consists of open magnetic fields and realistic temperature profile. The velocity perturbation of ≈ 68 km s ^-1 , resembling the observed velocity enhancement, launches a thin spicule-like jet whose properties closely match with the observed jet. We also show that non-adiabatic conditions (e.g., thermal conduction and radiative cooling) affect the jet propagation, mass flux, and kinetic energy density. We demonstrate that such spicule-like jets may transport mass and energy into the overlying solar atmosphere. The synthetic images derived from the use of simulation data (e.g., density, temperature) and atomic parameters of Si IV 1393.755 Å from CHIANTI database show that model jet consists of bright plasma as detected in the emissions at transition region temperature. It also consists of a cool core material that indicates its origin in the solar chromosphere. This cool chromospheric material appears as a dark plasma thread seen in the synthetic images that is eventually not evident in the Si IV emissions. IRIS Si IV emissions capture the heated counterpart of the observed jet, which is also evident in the synthetic images as a bright feature. Complementing the recent observations revealing the impulsive origin of the spicule-like jets, our present model emphasizes comprehensively their evolution in both adiabatic and non-adiabatic conditions of the solar atmosphere. The model implicitly displays the presence of the hot and cool components of jet’s plasma. It also demonstrates that the cooling atmosphere affects the kinematics and energetics of the jets.