Eruption-Related Ultraviolet Irradiance Enhancements Associated with Flares

TL;DR

This study quantifies the contribution of erupted material to ultraviolet irradiance enhancements during large solar flares, revealing that eruptions significantly impact UV emissions and suggesting multiple heating mechanisms.

Contribution

It provides the first quantitative analysis of erupted material's role in UV irradiance during flares, using a semi-automated masking method on multiple flare events.

Findings

Erupted material contributes 10-24% of radiated energy in UV channels.

Eruptions show little nonthermal heating signatures in HXR imaging.

Eruptions can significantly influence spectral variability in solar and stellar flares.

Abstract

Large solar flares (GOES M-class or higher) are usually associated with eruptions of material. However, when considering flare irradiance enhancements and dynamics such as chromospheric evaporation, potential contributions from erupted material have historically been neglected. We analyse nine eruptive M- and X-class flares from 2024 to early 2025, quantifying the relative contributions of erupted material to irradiance enhancements during the events. SDO/AIA images from four different channels had ribbon and eruption irradiance contributions separated using a semi-automated masking method. The sample-averaged percentages of excess radiated energy by erupted material over the impulsive phase were $10^{+4}_{-4}\%$, $24^{+14}_{-14}\%$, $21^{+14}_{-10}\%$ and $13^{+6}_{-9}\%$ for the $131\,$\r{A}, $171\,$\r{A}, $304\,$\r{A} and $1600\,$\r{A} channels, respectively. For three events that were studied in further detail, HXR imaging showed little to no signatures of nonthermal heating within the eruptions. Our results suggest that erupted material can be a significant contributor to UV irradiance enhancements during flares, with possible heating mechanisms including nonthermal particle heating, Ohmic heating, or dissipation of MHD waves. Future work may clarify the heating mechanism and evaluate the impact of eruptions on spectral variability, particularly in Sun-as-a-star and stellar flare observations.