arXiv subjects

Ryan O. Milligan

Publications and source records attributed to Ryan O. Milligan.

At least 19 recordsLinked to original sources

arXiv2026

The EUV Late-Phase: Statistical Results from 15 Years of Solar Dynamics Observatory Observations

Since its launch in 2010, the Solar Dynamics Observatory (SDO) has provided continuous, high-cadence, multi-wavelength observations of the Sun, capturing thousands of solar flares and offering new insights into coronal dynamics. Among the discoveries enabled by SDO is the EUV late-phase (ELP), characterised by a secondary enhancement in warm coronal emission occurring tens of minutes after the main flare. While recent work has demonstrated the relevance of the ELP for space weather, the statistical behaviours and physical origins are not fully understood. Here, we present the most comprehensive statistical analysis of the ELP to date, based on 15-years of Fe xvi (335 angstrom) observations from the Atmospheric Imaging Assembly onboard SDO (SDO/AIA). From a sample of 5335 isolated flares between 2010 and 2025, we identify and validate 467 ELP events. The overall ELP occurrence rate was found to be 9 percent, with no significant dependence on the solar cycle and only a modest enhancement in the low-mid M-class range. The ELP typically exhibited an onset delay of 19 minutes, a peak-to-peak delay of 88 minutes, and a duration of 93 minutes. Strong correlations were found between ELP rise and decay rates (p = 0.76), and between flare and ELP impulsivity (p = 0.61). However, a comprehensive pairwise analysis revealed no significant correlation between the flare and ELP phases. A Principal Component Analysis of flare and ELP properties identified several semi-independent axes of variability, broadly associated with late-phase temporal scale, impulsive heating characteristics, and the relative prominence of flare and late-phase intensity measures. These results highlight the continuing importance of SDO's long-term, high-resolution observations for uncovering new aspects of solar flare evolution and improving understanding of the Sun-Earth connection.

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arXiv2025

Observations of Flare Induced Doppler Shifts in the Si~\textsc{iii} $1206\,\textrm{Å}$ line

Doppler shifts in chromospheric and transition-region lines during solar flares are often interpreted as chromospheric condensation or evaporation. However, alternative sources of Doppler-shifted emission have been suggested, such as filament eruptions, jets or chromospheric bubbles. We analyse high-cadence scans from SORCE/SOLSTICE, which provide one-minute resolution profiles of the transition-region Si~\textsc{iii} ($1206\,\textrm{Å}$, $\textrm{T} = 10^{4.6}\,\textrm{K}$) line. 11 X-, M-, and C-class events observed during these scans with clear impulsive phase Si~\textsc{iii} enhancements were identified. By subtracting a quiet-Sun profile and fitting Gaussian profiles to the Si~\textsc{iii} line, measurements of flare-induced Doppler shifts were made. After correcting for a systematic trend in these shifts with solar longitude, two of the 11 events were found to exhibit a significant Doppler shift, \comment{}one with a $201.36\pm21.94\;\textrm{km\,s}^{-1}$ redshift and the other with a $-39.75\pm11.00\;\textrm{km\,s}^{-1}$ blueshift\commentend{}. Intriguingly, SDO/AIA $304\,\textrm{Å}$ and $1600\,\textrm{Å}$ imaging revealed a bright eruption coincident with the event that exhibited a blueshift, suggesting the shift may have resulted from the eruption rather than evaporation alone. Our results highlight Si~\textsc{iii} as a useful diagnostic of flaring dynamics at a temperature that has received limited attention to date. Future comparisons of these observations with radiative hydrodynamic simulations, along with new observations from state-of-the-art spectrometers such as SOLAR-C/EUVST and MUSE, should clarify the mechanisms behind the observed shifts in this study.

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arXiv2025

Investigating a Characteristic Time Lag in the Ionospheric F-region's Response to Solar Flares

X-ray and EUV solar flare emission cause increases in the Earth's dayside ionospheric electron density. While the response of the lower ionosphere to X-rays is well studied, the delay between EUV flare emission and the response of the ionospheric F-region has not been investigated. Here, we calculate the delays between incident He II 304 Angstrom emission, and the TEC response for 10 powerful solar flares, all of which exhibit delays under 1 minute. We assess these delays in relation to multiple solar and geophysical factors, and find a strong negative correlation (-0.85) between delay and He II flux change and a moderate negative correlation (-0.55) with rate of increase in He II flux. Additionally, flare magnitude and the X-ray-to-He II flux ratio at peak He II emission show strong negative correlations (-0.80 and -0.75, respectively). We also identify longer delays for flares occurring closer to the summer solstice. These results may have applications in upper-ionospheric recombination rate calculations, atmospheric modelling, and other solar-terrestrial studies. We highlight the importance of incident EUV and X-ray flux parameters on the response time of the ionospheric electron content, and these findings may also have implications for mitigating disruptions in communication and navigation systems.

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arXiv2025

Quasi-Periodic Pulsations in Ionospheric TEC Synchronized with Solar Flare EUV Emission

The extreme ultraviolet (EUV) and X-ray radiation emitted during solar flares has been shown to significantly increase the electron density of the Earth's ionosphere. During flares, quasi-periodic pulsations (QPPs) in X-ray flux originating in the corona have previously been linked to subsequent pulsations in the Earth's ionospheric D-region. Similar pulsations have been detected in chromospheric EUV emission, although their impact on the Earth's ionosphere has not previously been investigated. Here, for the first time, synchronous pulsations were detected in solar EUV emission and ionospheric Total Electron Content (TEC) measurements. Using wavelet and periodogram analysis, we detect QPPs with approximately 85 second periods in chromospheric EUV emission lines (He II 304 Å, C III 977 Å and H I 972 Å) from the Solar Dynamics Observatory Extreme Ultraviolet Variability Experiment (SDO/EVE) during the impulsive phase of an X5.4 flare on March 7, 2012. These lines contribute to ionization in the ionospheric E- and F-regions, resulting in subsequent variations of electron density with the same periodicity, which was detected in TEC measurements. This work demonstrates that the Earth's ionosphere is responsive to fine-scale fluctuations in EUV emission during flares, with a time delay of approximately 30 seconds found. These findings may have applications in atmospheric modelling and solar-terrestrial studies, including the calculation of ionospheric recombination rates.

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arXiv2024

On the Instrumental Discrepancies in Lyman-alpha Observations of Solar Flares

Despite the energetic significance of Lyman-alpha (Lyα; 1216Å) emission from solar flares, regular observations of flare related Lyα have been relatively scarce until recently. Advances in instrumental capabilities and a shift in focus over previous Solar Cycles mean it is now routinely possible to take regular co-observations of Lyα emission in solar flares. Thus, it is valuable to examine how the instruments selected for flare observations may influence the conclusions drawn from the analysis of their unique measurements. Here, we examine three M-class flares each observed in Lyα by GOES-14/EUVS-E, GOES-15/EUVS-E, or GOES-16/EXIS-EUVS-B, and at least one other instrument from PROBA2/LYRA, MAVEN/EUVM, ASO-S/LST-SDI, and SDO/EVE-MEGS-P. For each flare, the relative and excess flux, contrast, total energy, and timings of the Lyα emission were compared between instruments. It was found that while the discrepancies in measurements of the relative flux between instruments may be considered minimal, the calculated contrasts, excess fluxes, and energetics may differ significantly - in some cases up to a factor of five. This may have a notable impact on multi instrument investigations of the variable Lyα emission in solar flares and estimates of the contribution of Lyα to the radiated energy budget of the chromosphere. The findings presented in this study will act as a guide for the interpretation of observations of flare-related Lyα from upcoming instruments during future Solar Cycles and inform conclusions drawn from multi-instrument studies.

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arXiv2024

The Solar eruptioN Integral Field Spectrograph

The Solar eruptioN Integral Field Spectrograph (SNIFS) is a solar-gazing spectrograph scheduled to fly in the summer of 2025 on a NASA sounding rocket. Its goal is to view the solar chromosphere and transition region at a high cadence (1s) both spatially (0.5") and spectrally (33 mÅ) viewing wavelengths around Lyman Alpha (1216 Å), Si iii (1206 Å) and O v (1218 Å) to observe spicules, nanoflares, and possibly a solar flare. This time cadence will provide yet-unobserved detail about fast-changing features of the Sun. The instrument is comprised of a Gregorian-style reflecting telescope combined with a spectrograph via a specialized mirrorlet array that focuses the light from each spatial location in the image so that it may be spectrally dispersed without overlap from neighboring locations. This paper discusses the driving science, detailed instrument and subsystem design, and pre-integration testing of the SNIFS instrument.

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arXiv2023

Observational Analysis of Lyman-alpha Emission in Equivalent Magnitude Solar Flares

The chromospheric Lyman-alpha line of neutral hydrogen (Ly$α$; 1216 Å) is the most intense emission line in the solar spectrum, yet until recently observations of flare-related Ly$α$ emission have been scarce. Here, we examine the relationship between nonthermal electrons accelerated during the impulsive phase of three M3 flares that were co-observed by RHESSI, GOES, and SDO, and the corresponding response of the chromosphere in Ly$α$. Despite having identical X-ray magnitudes, these flares show significantly different Ly$α$ responses. The peak Ly$α$ enhancements above quiescent background for these flares were 1.5%, 3.3%, and 6.4%. However, the predicted Ly$α$ enhancements from FISM2 were consistently <2.5%. By comparing the properties of the nonthermal electrons derived from spectral analysis of hard X-ray observations, flares with a harder spectral index were found to produce a greater Ly$α$ enhancement. The percentage of nonthermal energy radiated by the Ly$α$ line during the impulsive phase was found to range from 2.0-7.9%. Comparatively, the radiative losses in He II (304 Å) were found to range from 0.6-1.4% of the nonthermal energy while displaying enhancements above the background of 7.3-10.8%. FISM2 was also found to underestimate the level of He II emission in two out of the three flares. These results may have implications for space weather studies and modelling the response of the terrestrial atmosphere to changes in the solar irradiance, and will guide the interpretation of flare-related Ly$α$ observations that will become available during Solar Cycle 25.

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arXiv2023

Spicules in IRIS Mg II Observations: Automated Identification

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 Hα 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 Hα spectral capabilities and upcoming Lyα 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.

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arXiv2023

Prospects of Detecting Non-thermal Protons in Solar Flares via Lyman Line Spectroscopy: Revisiting the Orrall-Zirker Effect

Solar flares are efficient particle accelerators, with a substantial fraction of the energy released manifesting as non-thermal particles. While the role that non-thermal electrons play in transporting flare energy is well studied, the properties and importance of non-thermal protons is rather less well understood. This is in large part due to the paucity of diagnostics, particularly at the lower-energy (deka-keV) range of non-thermal proton distributions in flares. One means to identify the presence of deka-keV protons is by an effect originally described by \cite{1976ApJ...208..618O}. In the Orrall-Zirker effect, non-thermal protons interact with ambient neutral hydrogen, and via charge exchange produce a population of energetic neutral atoms (ENAs) in the chromosphere. These ENAs subsequently produce an extremely redshifted photon in the red wings of hydrogen spectral lines. We revisit predictions of the strength of this effect using modern interaction cross-sections, and numerical models capable of self-consistently simulating the flaring non-equilibrium ionization stratification, and the non-thermal proton distribution (and, crucially, their feedback on each other). We synthesize both the thermal and non-thermal emission from \lya\ and \lyb, the most promising lines that may exhibit a detectable signal. These new predictions are are weaker and more transient than prior estimates, but the effects should be detectable in fortuitous circumstances. We degrade the \lyb\ emission to the resolution of the Spectral Imaging of the Coronal Environment (SPICE) instrument on board Solar Orbiter, demonstrating that though likely difficult, it should be possible to detect the presence of non-thermal protons in flares observed by SPICE.

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arXiv2023

Formation Of The Lyman Continuum During Solar Flares

The Lyman Continuum (LyC; $<911.12$Å) forms at the top of the chromosphere in the quiet-Sun, making LyC a powerful tool for probing the chromospheric plasma during solar flares. To understand the effects of non-thermal energy deposition in the chromosphere during flares, we analysed LyC profiles from a grid of field-aligned radiative hydrodynamic models generated using the RADYN code as part of the F-CHROMA project. The spectral response of LyC, the temporal evolution of the departure coefficient of hydrogen, $b_1$, and the color temperature, $T_c$, in response to a range of non-thermal electron distribution functions, were investigated. The LyC intensity was seen to increase by 4-5.5 orders of magnitude during solar flares, responding most strongly to the non-thermal electron flux of the beam. Generally, $b_1$ decreased from $10^2$-$10^3$ to closer to unity during solar flares, indicating a stronger coupling to local conditions, while $T_c$ increased from $8$-$9$kK to $10$-$16$kK. $T_c$ was found to be approximately equal to the electron temperature of the plasma when $b_1$ was at a minimum. Both optically thick and optically thin components of LyC were found in agreement with the interpretation of recent observations. The optically thick layer forms deeper in the chromosphere during a flare compared to quiescent periods, whereas the optically thin layers form at higher altitudes due to chromospheric evaporation, in low-temperature, high-density regions propagating upwards. We put these results in the context of current and future missions.

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arXiv2022

Call and Response: A Time-Resolved Study of Chromospheric Evaporation in a Large Solar Flare

We studied an X1.6 solar flare produced by NOAA AR 12602 on 2014 October 22. The entirety of this event was covered by RHESSI, IRIS, and Hinode/EIS, allowing analysis of the chromospheric response to a nonthermal electron driver. We derived the energy contained in nonthermal electrons via RHESSI spectral fitting, and linked the time-dependent parameters of this call to the response in Doppler velocity, density, and nonthermal width across a broad temperature range. The total energy injected was $4.8\times10^{30}$ erg, and lasted $352$ seconds. This energy drove explosive chromospheric evaporation, with a delineation in both Doppler and nonthermal velocities at the flow reversal temperature, between 1.35--1.82 MK. The time of peak electron injection (14:06 UT) corresponded to the time of highest velocities. At this time, we found 200 km s$^{-1}$ blueshifts in the core of Fe XXIV, which is typically assumed to be at rest. Shortly before this time, the nonthermal electron population had the shallowest spectral index ($\approx$ 6), corresponding to the peak nonthermal velocity in Si IV and Fe XXI. Nonthermal velocities in Fe XIV, formed near the flow reversal temperature were low, and not correlated with density or Doppler velocity. Nonthermal velocities in ions with similar temperatures were observed to increase and correlate with Doppler velocities, implying unresolved flows surrounding the flow reversal point. This study provides a comprehensive, time-resolved set of chromospheric diagnostics for a large X-class flare, along with a time-resolved energy injection profile, ideal for further modeling studies.

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arXiv2021

Flare Induced Sunquake Signatures in the Ultraviolet as Observed by the Atmospheric Imaging Assembly

Sunquakes (SQs) have been routinely observed in the solar photosphere, but it is only recently that signatures of these events have been detected in the chromosphere. We investigate whether signatures of SQs are common in Ultraviolet (UV) continua, which sample the solar plasma several hundred km above where SQs are typically detected. We analyse observations from the Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA) 1600 Å and 1700 Å passbands, for SQ signatures induced by the flares of Solar Cycle 24. We base our analysis on the 62 SQs detected in the recent statistical study presented by Sharykin & Zosovichev (2020). We find that 9 out of 62 SQ candidates produced a response that is clearly detected in running difference images from the AIA 1600 Å and 1700 Å channels. A binary frequency filter with a width of 2 mHz, centred on 6 mHz, was applied to the data. The first signature of each SQ was detected at distances between 5.2 Mm to 25.7 Mm from the associated flare ribbon. Time-distance and regression analysis allowed us to calculate the apparent transverse velocities of the SQs in the UV datasets and found maximum velocities as high as 41 km s-1, 87 Mm away from the SQ source. Our analysis shows that flare induced SQ signatures can be detected in the SDO/AIA 1600 Å and 1700 Å passbands, hinting at their presence in the lower chromosphere. There was no apparent correlation between GOES flare classification, and the appearance of the SQ at these heights.

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arXiv2021

Solar Irradiance Variability Due To Solar Flares Observed in Lyman-alpha Emission

As the Lyman-alpha (Lya) line of neutral hydrogen is the brightest emission line in the solar spectrum, detecting increases in irradiance due to solar flares at this wavelength can be challenging due to the very high background. Previous studies that have focused on the largest flares have shown that even these extreme cases generate enhancements in Lya of only a few percent above the background. In this study, a superposed-epoch analysis was performed on ~8500 flares greater than B1 class to determine the contribution that flares make to changes in the solar EUV irradiance. Using the peak of the 1-8A X-ray emission as a fiducial time, the corresponding time series of 3123 B- and 4972 C-class flares observed in Lya emission by the EUV Sensor on GOES-15 were averaged to reduce background fluctuations and improve the flare signal. The summation of these weaker events showed that they produced a 0.1-0.3% enhancement to the solar Lya irradiance. For comparison on average, the same technique was applied to 453 M- and 31 X-class flares, which resulted in a 1-4% increase in Lya emission. Flares were also averaged with respect to their heliographic angle to investigate any potential center-to-limb variation. For each GOES class, the relative enhancement in Lya at the flare peak was found to diminish for flares that occurred closer to the solar limb due to the opacity of the line, and/or foreshortening of the footpoints. One modest event included in the study, a C6.6 flare, exhibited an unusually high increase in Lya of 7% that may have been attributed to a failed filament eruption. Increases of this magnitude have hitherto only been associated with a small number of X-class flares.

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arXiv2020

Solar Flare Energy Partitioning and Transport -- the Impulsive Phase (a Heliophysics 2050 White Paper)

Solar flares are a fundamental component of solar eruptive events (SEEs; along with solar energetic particles, SEPs, and coronal mass ejections, CMEs). Flares are the first component of the SEE to impact our atmosphere, which can set the stage for the arrival of the associated SEPs and CME. Magnetic reconnection drives SEEs by restructuring the solar coronal magnetic field, liberating a tremendous amount of energy which is partitioned into various physical manifestations: particle acceleration, mass and magnetic-field eruption, atmospheric heating, and the subsequent emission of radiation as solar flares. To explain and ultimately predict these geoeffective events, the heliophysics community requires a comprehensive understanding of the processes that transform and distribute stored magnetic energy into other forms, including the broadband radiative enhancement that characterises flares. This white paper, submitted to the Heliophysics 2050 Workshop, discusses the flare impulsive phase part of SEEs, setting out the questions that need addressing via a combination of theoretical, modelling, and observational research. In short, by 2050 we must determine the mechanisms of particle acceleration and propagation, and must push beyond the paradigm of energy transport via nonthermal electron beams, to also account for accelerated protons & ions and downward directed Alfven waves.

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arXiv2020

Solar Flare Energy Partitioning and Transport -- the Gradual Phase (a Heliophysics 2050 White Paper)

Solar flares are a fundamental component of solar eruptive events (SEEs; along with solar energetic particles, SEPs, and coronal mass ejections, CMEs). Flares are the first component of the SEE to impact our atmosphere, which can set the stage for the arrival of the associated SEPs and CME. Magnetic reconnection drives SEEs by restructuring the solar coronal magnetic field, liberating a tremendous amount of energy which is partitioned into various physical manifestations: particle acceleration, mass and magnetic-field eruption, atmospheric heating, and the subsequent emission of radiation as solar flares. To explain and ultimately predict these geoeffective events, the heliophysics community requires a comprehensive understanding of the processes that transform and distribute stored magnetic energy into other forms, including the broadband radiative enhancement that characterises flares. This white paper, submitted to the Heliophysics 2050 Workshop, discusses the flare gradual phase part of SEEs, setting out the questions that need addressing via a combination of theoretical, modelling, and observational research. In short, the flare gradual phase persists much longer than predicted so, by 2050, we must identify the characteristics of the significant energy deposition sustaining the gradual phase, and address the fundamental processes of turbulence and non-local heat flux.

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arXiv2020

The effect of a solar flare on chromospheric oscillations

Oscillations in the solar atmosphere have long been observed in quiet conditions, and increasingly also in data taken during solar flares. The chromosphere is known for its 3-minute signals, which are particularly strong over sunspot umbrae. These signals are thought to be driven by photospheric disturbances and their periods determined by the chromosphere's acoustic cut-off frequency. A small number of observations have shown the chromospheric 3-minute signals to be affected by energetic events such as solar flares, however the link between flare activity and these oscillatory signals remains unclear. In this work we present evidence of changes to the oscillatory structure of the chromosphere over a sunspot which occurs during the impulsive phase of an M1 flare. Using imaging data from the CRISP instrument across the H$α$ and Ca II 8542 Å spectral lines, we employed a method of fitting models to power spectra to produce maps of areas where there is evidence of oscillatory signals above a red noise background. Comparing results taken before and after the impulsive phase of the flare, we found that the oscillatory signals taken after the start of the flare differ in two ways: the locations of oscillatory signals had changed and the typical periods of the oscillations had tended to increase (in some cases increasing from $\lt$100s to $\sim$200s). Both of these results can be explained by a restructuring of the magnetic field in the chromosphere during the flare activity, which is backed up by images of coronal loops showing clear changes to magnetic connectivity. These results represent one of the many ways that active regions can be affected by solar flare events.

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arXiv2020

Lyman-alpha Variability During Solar Flares Over Solar Cycle 24 Using GOES-15/EUVS-E

The chromospheric Lyman-alpha line of neutral hydrogen (\lya; 1216Å) is the strongest emission line in the solar spectrum. Fluctuations in \lya\ are known to drive changes in planetary atmospheres, although few instruments have had the ability to capture rapid \lya\ enhancements during solar flares. In this paper we describe flare-associated emissions via a statistical study of 477 M- and X-class flares as observed by the EUV Sensor on board the 15th Geostationary Operational Environmental Satellite, which has been monitoring the full-disk solar \lya\ irradiance on 10~s timescales over the course of Solar Cycle 24. The vast majority (95\%) of these flares produced \lya\ enhancements of 10\% or less above background levels, with a maximum increase of $\sim$30\%. The irradiance in \lya\ was found to exceed that of the 1-8 Å X-ray irradiance by as much as two orders of magnitude in some cases, although flares that occurred closer to the solar limb were found to exhibit less of a \lya\ enhancement. This center-to-limb variation was verified through a joint, stereoscopic observation of an X-class flare that appeared near the limb as viewed from Earth, but close to disk center as viewed by the MAVEN spacecraft in orbit around Mars. The frequency distribution of peak \lya\ was found to have a power-law slope of $2.8\pm0.27$. We also show that increased \lya\ flux is closely correlated with induced currents in the ionospheric E-layer through the detection of the solar flare effect as observed by the Kakioka magnetometer.

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arXiv2018

The spectral content of SDO/AIA 1600 and 1700 Å filters from flare and plage observations

The strong enhancement of the ultraviolet emission during solar flares is usually taken as an indication of plasma heating in the lower solar atmosphere caused by the deposition of the energy released during these events. Images taken with broadband ultraviolet filters by the {\em Transition Region and Coronal Explorer} (TRACE) and {\em Atmospheric Imaging Assembly} (AIA 1600 and 1700~Å) have revealed the morphology and evolution of flare ribbons in great detail. However, the spectral content of these images is still largely unknown. Without the knowledge of the spectral contribution to these UV filters, the use of these rich imaging datasets is severely limited. Aiming to solve this issue, we estimate the spectral contributions of the AIA UV flare and plage images using high-resolution spectra in the range 1300 to 1900~Å from the Skylab NRL SO82B spectrograph. We find that the flare excess emission in AIA 1600~Å is { dominated by} the \ion{C}{4} 1550~Å doublet (26\%), \ion{Si}{1} continua (20\%), with smaller contributions from many other chromospheric lines such as \ion{C}{1} 1561 and 1656~Å multiplets, \ion{He}{2} 1640~Å, \ion{Si}{2} 1526 and 1533~Å. For the AIA 1700~Å band, \ion{C}{1} 1656~Å multiplet is the main contributor (38\%), followed by \ion{He}{2} 1640 (17\%), and accompanied by a multitude of other, { weaker} chromospheric lines, with minimal contribution from the continuum. Our results can be generalized to state that the AIA UV flare excess emission is of chromospheric origin, while plage emission is dominated by photospheric continuum emission in both channels.

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