Spicule widths from high-resolution Ca II K observations

Solar spicules are as puzzling as they are ubiquitous. These long, jet-like features are the dominant off-limb features in chromospheric filtergrams and can also be seen on disk in narrowband images taken near the cores of chromospheric lines. Several scenarios of spicule formation predict that they are a manifestation, or associated with, magnetic flux tubes. Such tubes are presumed to expand in width from the photosphere to the corona, as the magnetic pressure dominates over gas pressure, possibly leading to an increase of spicular width with height. Other scenarios predict that spicules result from a release of magnetic tension and their widths slowly decrease with height. Observations from Hinode and IRIS do not show a clear change in spicule width with height, although individual spicules are difficult to isolate at the limb and the typical widths are already close to the instrument spatial resolution. In this work we revisit the topic of spicular width as a function of height using some of the highest resolution observations currently available. We make use of Ca II K spectroheliograms, taken with the CHROMIS instrument at the Swedish 1-m Solar Telescope, to measure widths of several spicules. We also discuss how widths vary with narrowband position along the spectral line, and compare the spectral properties of spicules in Ca II K with earlier work in Halpha.