INTERPLAY OF THREE KINDS OF MOTION IN THE DISK COUNTERPART OF TYPE II SPICULES: UPFLOW, TRANSVERSAL, AND TORSIONAL MOTIONS

Abstract

Recently, it was shown that the complex dynamical behaviour of spicules has\nto be interpreted as the result of simultaneous action of three kinds of\nmotion: (1) field aligned flows, (2) swaying motions, and (3) torsional\nmotions. We use high-quality observations from CRISP at the SST to investigate\nsigns of these different kinetic modes in spicules on the disk. Earlier, rapid\nblue-shifted excursions (RBEs), short-lived absorption features in the blue\nwing of chromospheric spectral lines, were identified as the disk counterpart\nof type II spicules. Here we report the existence of similar absorption\nfeatures in the red wing of the Ca II 8542 and Halpha lines: rapid red-shifted\nexcursions (RREs). RREs are found over the whole solar disk and are located in\nthe same regions as RBEs: in the vicinity of magnetic field concentrations.\nRREs have similar characteristics as RBEs: they have similar lengths, widths,\nlifetimes, and average Doppler velocity. The striking similarity of RREs to\nRBEs implies that RREs are a manifestation of the same physical phenomenon and\nthat spicules harbour motions that can result in a net red-shift when observed\non-disk. We find that RREs are less abundant than RBEs and we interpret the\nhigher number of RBEs and the decreased imbalance towards the limb as an\nindication that field-aligned up-flows have a significant contribution to the\nnet Dopplershift. Most RREs and RBEs are observed in isolation but we find many\nexamples of parallel and touching RRE/RBE pairs which appear to be part of the\nsame spicule. We interpret the existence of these RRE/RBE pairs as signs that\ntorsional motion is an important characteristic of spicules. The fact that most\nRBEs and RREs are observed in isolation agrees with the idea that transversal\nswaying motion is another important kinetic mode. We find examples of\ntransitions from RRE to RBE and vice versa.\n