Abstract
Solar spicules are chromospheric jets of up-flowing plasma observed all over the Sun, and can be categorized into type i and type ii spicules. Type ii spicules are more dynamic and more ubiquitous, yet their origin and ubiquity are not understood. We use, for the first time, high-resolution observations of type ii spicules in Ca ii K 393.4 nm to characterize the bright/dark (B/D) characteristics we observe in Ca ii K spicules. We also compare the apparent length of spicules in Ca ii K to spicules in Hα. The observations are of the quiet Sun close to the limb (µ = 0.41) and were acquired by the CHROMospheric Imaging Spectrometer (CHROMIS) and the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish 1-metre Solar Telescope on La Palma. We find that the B/D characteristics are evident due to suppression of the K2 peak in the upper part corresponding to the K3 Doppler shift, combined with significant enhancement of that same K2 peak along the lower part of the spicule, yielding a direct demonstration of heating along the spicule. We often see the effect of enhanced K2 peaks in upper parts of spicules due to the “opacity window” reported by Bose et al. (2019), but we also sometimes observe enhanced upper K2 peaks from the bright surroundings or the spicule itself. Out of 39 spicules, we do not see this “window”-effect for the lower parts of spicules, except one spicule where we see enhancement of lower part K2 due to neighbouring spicule in the background. We also found that spicules appear a little longer in Ca ii K than Hα due to the signal generally reaching higher in Ca ii K but they also appear to reach deeper due to the brightening in the bottom.
Veiledere: FørsteamanuensisTiago Pereira og professor Luc Rouppe van der Voort, Institutt for teoretisk astrofysikk, UiO
Intern sensor: Professor Boris Vilhelm Gudiksen, Institutt for teoretisk astrofysikk, UiO
Ekstern sensor: Assistant Director Dan Kiselman, Institute for Solar Physics, Stockholm University