A Multi-wavelength Analysis of Small-scale Brightenings Observed by IRIS

Abstract

Small-scale brightenings in solar atmospheric observations are a manifestation of heating and/or energy transport events. We present statistical characteristics of brightenings from a new detection method applied to 1330, 1400, and 2796 Å IRIS slit-jaw image time series. A total of 2377 events were recorded that coexist in all three channels, giving high confidence that they are real. Of these, ≈1800 were spatially coherent, equating to event densities of ∼9.7 × 10−5 arcsec−2 s−1 within a 90″ × 100″ FOV over 34.5 minutes. Power-law indices estimates are determined for total brightness (2.78 < α < 3.71), maximum brightness (3.84 < α < 4.70), and average area (4.31 < α < 5.70) distributions. Duration and speed distributions do not obey a power law. A correlation is found between the events’ spatial fragmentation, area, and duration, and a weak relationship with total brightness, showing that larger/longer-lasting events are more likely to fragment during their lifetime. Speed distributions show that all events are in motion, with an average speed of ∼7 km s−1. The events’ spatial trajectories suggest that cooler 2796 Å events tend to appear slightly later and occupy a different position/trajectory than the hotter channel results. This suggests that either many of these are impulsive events caused by reconnection, with subsequent rapid cooling, or that the triggering event occurs near the TR, with a subsequent propagating disturbance to cooler atmospheric layers. The spatial distribution of events is not uniform, with broad regions devoid of events. A comparison of spatial distribution with properties of other atmospheric layers shows a tentative connection between high magnetic field strength, the corona’s multi-thermality, and high IRIS brightening activity.

SolO/EUI Observations of Ubiquitous Fine-scale Bright Dots in an Emerging Flux Region: Comparison with a Bifrost MHD Simulation

“…Of particular interest would be assessing Doppler speeds of dots in different atmospheric heights using IRIS spectra and comparing those with that of Bifrost MHD simulations. Furthermore, sophisticated techniques, such as those presented by Humphries & Morgan (2021) for automatically selecting and characterizing a large number of brightenings, should be used in the future on a much larger sample of dots to assess their common characteristics and corroborate our findings.…”

SolO/EUI Observations of Ubiquitous Fine-scale Bright Dots in an Emerging Flux Region: Comparison with a Bifrost MHD Simulation

“…Of particular interest would be assessing Doppler speeds of dots in different atmospheric heights using IRIS spectra and comparing those with that of Bifrost MHD simulations. Furthermore, sophisticated techniques, such as those presented by Humphries & Morgan (2021) for automatically selecting and characterizing a large number of brightenings, should be used in future on a much larger sample of dots to assess their common characteristics and corroborate our findings.…”

Preliminary Discussion on the Current Sheet

“…Furthermore, the observed current sheet is an emission-enhanced region (Chae et al 2017;Patel et al 2020), and the emission intensity is related to the plasma temperature or density (Plowman & Caspi 2020;Bemporad et al 2022). For the region where the magnetic reconnection is violent, more plasma flows are introduced into the reconnection layer and more magnetic field energy is released to heat the plasmas (Mackay et al 2010;Takasao et al 2012), which contributes to a brightened region of strong emission (Humphries & Morgan 2021;Cheng et al 2023). In other segments of the current sheet, however, the emission is weak and decays quickly (see Figures 5(a) and (b)).…”