Searching for signatures of H α spicule-like features in the solar transition region

Abstract

ABSTRACT New instruments and telescopes covering the optical and ultraviolet spectral regions have revealed a range of small-scale dynamic features, many which may be related. For example, the range of spicule-like features hints towards a spectrum of features and not just two types; however, direct observational evidence in terms of tracking spicules across multiple wavelengths is needed in order to provide further insight into the dynamics of the Sun’s outer atmosphere. This paper uses H α data obtained with the CRisp Imaging SpectroPolarimeter instrument on the Swedish 1-m Solar Telescope, and in the transition region using the Interface Region Imaging Spectrograph with the SJI 1400 Å channel plus spectral data via the Si iv 1394 Å line to track spicules termed rapid blueshifted excursions (RBEs). The RBEs as seen in the H α blue wing images presented here can be subdivided into two categories: a single or multithreaded feature. Based on the H α spectra, the features can be divided into events showing broadening and line core absorption, events showing broadening and line core emission, events with a pure blueshifted H α profile without any absorption in the red wing, and broadened line profile with the absorption in the blue stronger compared to the red wing. From the RBE-like events that have a Si iv 1394 Å line profile, 78  per cent of them show a Si iv line flux increase. Most of these features show a second broadened Si iv component that is slightly blueshifted.