High-cadence observations of spicular-type events on the Sun

¹ Armagh Observatory, College Hill, Armagh BT61 9DG, UK
e-mail: jus@arm.ac.uk
² School of Physics, Trinity College Dublin, Dublin 2, Ireland
³ Solar Physics and Space Plasma Research Centre, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH, UK
⁴ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, BT7 1NN, UK
⁵ NSO/DKIST, University of Colorado at Boulder, 3665 Discovery Drive, Boulder, CO 80303, USA
⁶ Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
⁷ Department of Mathematics & Information Sciences, Northumbria University, Newcastle Upon Tyne, NE1 8ST, UK

Received: 5 October 2015
Accepted: 18 February 2016

Abstract

Context. Chromospheric observations taken at high-cadence and high-spatial resolution show a range of spicule-like features, including Type-I, Type-II (as well as rapid blue-shifted excursions (RBEs) and rapid red-shifted excursions (RREs) which are thought to be on-disk counterparts of Type-II spicules) and those which seem to appear within a few seconds, which if interpreted as flows would imply mass flow velocities in excess of 1000 km s^-1.

Aims. This article seeks to quantify and study rapidly appearing spicular-type events. We also compare the multi-object multi-frame blind deconvolution (MOMFBD) and speckle reconstruction techniques to understand if these spicules are more favourably observed using a particular technique.

Methods. We use spectral imaging observations taken with the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1-m Solar Telescope. Data was sampled at multiple positions within the Hα line profile for both an on-disk and limb location.

Results. The data is host to numerous rapidly appearing features which are observed at different locations within the Hα line profile. The feature’s durations vary between 10–20 s and lengths around 3500 km. Sometimes, a time delay in their appearance between the blue and red wings of 3–5 s is evident, whereas, sometimes they are near simultaneous. In some instances, features are observed to fade and then re-emerge at the same location several tens of seconds later.

Conclusions. We provide the first statistical analysis of these spicules and suggest that these observations can be interpreted as the line-of-sight (LOS) movement of highly dynamic spicules moving in and out of the narrow 60 mÅ transmission filter that is used to observe in different parts of the Hα line profile. The LOS velocity component of the observed fast chromospheric features, manifested as Doppler shifts, are responsible for their appearance in the red and blue wings of Hα line. Additional work involving data at other wavelengths is required to investigate the nature of their possible wave-like activity.