Plasma dynamics in solar macrospicules from high-cadence extreme-UV observations

Abstract

Macrospicules are relatively large spicule-like formations found mainly over the polar coronal holes when observing in the transition region spectral lines. In this study, we took advantage of the two short series of observations in the He II 304 \r{A} line obtained by the TESIS solar observatory with a cadence of up to 3.5 s to study the dynamics of macrospicules in unprecedented detail. We used a one-dimensional hydrodynamic method based on the assumption of their axial symmetry and on a simple radiative transfer model to reconstruct the evolution of the internal velocity field of 18 macrospicules from this dataset. Besides the internal dynamics, we studied the motion of the apparent end points of the same 18 macrospicules and found 15 of them to follow parabolic trajectories with high precision which correspond closely to the obtained velocity fields. We found that in a clear, unperturbed case these macrospicules move with a constant deceleration inconsistent with a purely ballistic motion and have roughly the same velocity along their entire axis, with the obtained decelerations typically ranging from 160 to 230 m/s^2, and initial velocities from 80 to 130 km/s. We also found a propagating acoustic wave for one of the macrospicules and a clear linear correlation between the initial velocities of the macrospicules and their decelerations, which indicates that they may be driven by magneto-acoustic shocks. Finally, we inverted our previous method by taking velocities from the parabolic fits to give rough estimates of the percentage of mass lost by 12 of the macrospicules. We found that typically from 10 to 30% of their observed mass fades out of the line (presumably being heated to higher coronal temperatures) with three exceptions of 50% and one of 80%.