Detecting and Characterising Small-Scale Brightenings in Solar Imaging Data

Observations of small-scale brightenings in the low solar atmosphere can provide valuable constraints on possible heating/heat-transport mechanisms. We present a method for the detection and analysis of brightenings and demonstrate its application to IRIS EUV time-series imagery. The method uses band-pass filtering, adaptive thresholding and centroid tracking, and records an event's position, duration, and total/maximum brightness. Area, brightness, and position are also recorded as functions of time throughout their lifetime. Detected brightenings can fragment or merge over time, thus the number of distinct regions constituting a brightening event is recorded over time and the maximum number of regions are recorded as a simple measure of an event's coherence/complexity. A test is made on a synthetic datacube composed of a static background based on IRIS data, Poisson noise and $\approx10^4$ randomly-distributed, moving, small-scale Gaussian brightenings. Maximum brightness, total brightness, area, and duration follow power-law distributions and the results show the range over which the method can extract information. The recorded maximum brightness is a reliable measure for the brightest and most accurately detected events with an error of 6%. Area, duration, and speed are generally underestimated by 15% with an uncertainty of 20-30%. Total brightness is underestimated by 30% with an uncertainty of 30%. Applying this method to real IRIS QS data spanning 19 minutes over a 54.40"$\times$55.23" FOV yields 2997 detections. 1340 of these either remain un-fragmented or fragment to two distinct regions at least once during their lifetime equating to an event density of $3.96\times10^{-4}$arcsec$^{-2}$s$^{-1}$. The method will be used for a future large-scale statistical analysis of several QS data sets from IRIS, other EUV imagers, as well as H-$\alpha$ and visible photospheric imagery.Comment: 19 pages, 12 figure

Multi-wavelength imaging and spectral analysis of jet-like phenomena in a solar active region using IRIS and AIA

High-resolution observations of dynamic phenomena give insights into the properties and processes that govern the low solar atmosphere. We present an analysis of jet-like phenomena emanating from a penumbral footpoint in active region (AR) 12192 using imaging and spectral observations from the Interface Region Imaging Spectrograph (IRIS) and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. These jets are associated with line-of-sight Doppler speeds of ±10–22 km s−1 and bright fronts that seem to move across the plane-of-sky at speeds of 23–130 km s−1. Such speeds are considerably higher than the expected sound speed in the chromosphere. The jets have signatures that are visible both in the cool and hot channels of IRIS and AIA. Each jet lasts on average 15 minutes and occurs 5–7 times over a period of 2 hr. Possible mechanisms to explain this phenomenon are suggested, the most likely of which involve p-mode or Alfvén wave shock trains impinging on the transition region and corona as a result of steepening photospheric wavefronts or gravity waves