Understanding the Structure of Rapid Intensity Fluctuations in the Chromosphere with IRIS

Abstract

Abstract Several recent data sets have taken advantage of the unique capabilities of orbital and suborbital spacecraft to image the chromosphere and transition region at a very high cadence. We find that both the chromosphere and transition region exhibit spatially coherent transient features at frequencies above 80 mHz. We have analyzed narrowband imaging data from H i Lyα 1215 Å (provided by CLASP), Mg ii k 2796 Å, and Si iv 1400 Å (provided by the Interface Region Imaging Spectrograph). We categorize the spatial structure of these rapid fluctuations in different magnetic environments. Intensity fluctuations above the noise level are observed in plages in all passbands. We have found jet-like features in 1215 and 1400 Å data that extend from the edges of plages as well as network magnetic concentrations. We have not found any recurrent features that are identified in both 1400 and 1215 Å data. Short loop-like features were only found in 1400 Å data. Temperature minimum grains generate non-propagating features in 1400 Å data. We compare our observations with previous research on dynamic chromospheric phenomena at lower frequencies. Candidate mechanisms, related to both jets and waves, predict chromospheric and transition region intensity fluctuations at high temporal frequencies, which can now be observationally probed.