Spicules in IRIS Mg ii Observations: Automated Identification

Abstract

We have developed an algorithm to identify solar spicules in the first ever systematic survey of on-disk spicules exclusively using Mg ii spectral observations. Using this algorithm we identify 2021 events in three Interface Region Imaging Spectrograph (IRIS) data sets with unique solar feature targets spanning a total of 300 minutes: (1) active region, (2) decayed active region/active network, and (3) coronal hole. We present event statistics and relate occurrence rates to the underlying photospheric magnetic field strength. This method identifies spicule event densities and occurrence rates similar to previous studies performed using H α and Ca ii observations of active regions. Additionally, this study identifies spicule-like events at very low rates at magnetic field intensities below 20 G, and increasing significantly between 100 and 200 G in active regions and above 20 G in coronal holes, which can be used to inform future observation campaigns. This information can be be used to help characterize spicules over their full lifetimes, and compliments existing H α spectral capabilities and upcoming Ly α spectral observations with the Solar eruptioN Integral Field Spectrograph (SNIFS) sounding rocket. In total, this study presents a method for detecting solar spicules exclusively using Mg ii spectra, and provides statistics for spicule occurrences in the Mg ii h line with respect to the magnetic field strength for the purpose of predicting spicule occurrences.

Keywords

• Solar spicules
• Solar chromosphere
• Solar transition region
• Solar atmosphere
• Solar coronal heating
• Solar magnetic fields