Daniel B. Seaton

Solar extreme ultraviolet (EUV) irradiance predominantly originates from the chromosphere and corona, and variations in EUV irradiance are a significant driver of space weather at Earth, causing increased satellite drag, radio communication disruptions, and reduced GPS accuracy. Since solar EUV irradiance measurements are intermittent and inhomogeneous, models are used to fill spectral and temporal gaps, typically relying on proxy-based methods that utilize linear correlations between emission originating from similar heights or temperatures in the solar atmosphere. Proxy methods can struggle to capture dynamic irradiance variations of the solar corona during flares in part due to the relative infrequency of flares on which to derive correlations and the steep temporal temperature gradients experienced during flares. This paper presents a hybrid method for modeling solar EUV irradiance utilizing forward-modeled physics-informed solar differential emission measures (DEMs) to capture the optically thin coronal emission coupled with traditional proxy-based correlation methods to capture the chromospheric and continuum emission. The model is trained and tested using inputs from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) and EUV Variability Experiment (EVE) and compared against a proxy-only method. The results demonstrate that including information from DEMs into a EUV irradiance model improves accuracy for flaring conditions, particularly for high-temperature coronal lines, where the model error is reduced by up to a factor of 3 for M- and X-class flares compared to a proxy-only model trained on the same data.

We perform a detailed study of the energetics for a well-observed solar eruption and flare that occurred on 2021 October 28. This event included a GOES class X1.0 flare, a global extreme-UV (EUV) wave, and a coronal mass ejection (CME) that reached speeds of >2000 km s ⁻¹ . The event was observed from a variety of spacecraft in NASA’s Heliophysics System Observatory, including multiple missions near Earth, STEREO-A off the Sun-Earth line, and Solar Orbiter, near the Sun-Earth line at about 0.8 au. Using remote sensing, in situ observations, and in some cases scaling laws based on previous observations, we characterize the following quantities: free magnetic energy, energy in nonthermal electrons, energy in nonthermal ions, bolometric energy, energy deposited in the chromosphere, thermal energy radiated in the flare loops, energy dissipated by the EUV wave, CME kinetic and gravitational potential energy, CME energy flux in the heliosphere, and the energy partition in the CME shock. We find that the total energy released during the event is consistent with estimates of the pre-event stored magnetic energy, and the CME kinetic + potential energy dominates the energy partition.

We present an extension of the Coronal Reconstruction Onto B-Aligned Regions (CROBAR) method to Linear Force Free Field (LFFF) extrapolations, and apply it to the reconstruction of a set of Atmospheric Imaging Assembly, Michelson Doppler Imager, and STEREO EUVI data. The results demonstrate that CROBAR is not only capable of reconstructing coronal emission structures, but also the previously made claim that it can constrain coronal field extrapolations, in this case the LFFF’s α parameter. They also provide a real-world example of how CROBAR can easily incorporate information from multiple perspectives to improve its reconstructions, and we also use the additional perspectives to help validate the reconstructions. We furthermore touch on the use of real-world emission passbands rather than idealized power-law type ones using differential emission measures (DEMs). We conclude with a comparison of CROBAR-generated emission to observed emission and those produced with idealized DEM based power laws. These results further illustrate the promise of CROBAR for real-world applications, and we make available a preliminary release of the software available for download.

The Polarimeter to Unify the Corona and Heliosphere (PUNCH) mission is a NASA Small Explorer to determine the cross-scale processes that unify the solar corona and heliosphere. PUNCH has two science objectives: (1) understand how coronal structures become the ambient solar wind, and (2) understand the dynamic evolution of transient structures, such as coronal mass ejections, in the young solar wind. To address these objectives, PUNCH uses a constellation of four small spacecraft in Sun-synchronous low Earth orbit, to collect linearly polarized images of the K corona and young solar wind. The four spacecraft each carry one visible-light imager in a 1 + 3 configuration: a single Narrow Field Imager solar coronagraph captures images of the outer corona at all position angles, and at solar elongations from 1.5° (6 R _⊙ ) to 8° (32 R _⊙ ); and three separate Wide Field Imager heliospheric imagers together capture views of the entire inner solar system, at solar elongations from 3° (12 R _⊙ ) to 45° (180 R _⊙ ) from the Sun. PUNCH images include linear-polarization data, to enable inferring the three-dimensional structure of visible features without stereoscopy. The instruments are matched in wavelength passband, support overlapping instantaneous fields of view, and are operated synchronously, to act as a single “virtual instrument” with a 90 ^∘ wide field of view, centered on the Sun. PUNCH launched in March of 2025 and began science operations in June of 2025. PUNCH has an open data policy with no proprietary period, and PUNCH Science Team Meetings are open to all.

We investigate the aftermath of a giant quiescent solar filament eruption on 2023 December 24. One feature of the eruption is an extensive fan above the filament channel that is about 3 times as wide as similar structures that appear above active regions (ARs) during solar flares. The fan contains numerous supra-arcade downflows (SADs), and we investigate the largest SADs with continuous Hinode X-ray Telescope observations. The measured maximum width of the SADs in this event is at least 3 times the maximum width of SADs observed in AR flares, whereas the velocities of the largest SADs are similar to the typical values of AR SADs. The kinetic characteristics of the largest SADs observed in this event align with previous model predictions, where SADs originate from the nonlinear development of Rayleigh–Taylor-type instabilities. In this scenario, the larger system size allows the existence of larger-scale instabilities, while the development of the velocities of these instabilities is expected to be independent of the system size. Compared to AR flares, the temperature and emission measure in this event are lower, and there is less overall radiation, resulting in no evident Geostationary Operational Environmental Satellite signature. Similar to those in AR flares, SADs show lower temperatures compared to the surrounding fan plasma. Our observations show that SADs are present in a wide variety of eruptions. The reconnection mechanisms present in quiescent filament eruptions are similar to those driving more compact eruptions originating from ARs.

Recent observations reveal small-scale reconnection-driven plasma ejections, often termed nanojets, triggered by magnetic field interactions at slight misalignment angles. These fast, collimated plasma ejections are ∼1.5 Mm long and ∼0.5 Mm wide. In this study, we analyze two high-resolution extreme ultraviolet imaging data sets from the Extreme Ultraviolet Imager on board the Solar Orbiter mission, corresponding to an eruptive (M7.6) and a confined (C1.2) flare, to investigate the dynamics of nanoflare ejections and, for the first time, compare their properties in distinct magnetic environments. We identified 59 nanoflare ejections: 44 in the eruptive flare and 15 in the confined flare event. Our analysis reveals that these events form two distinct classes: confined events exhibit lower speeds (41–174 km s⁻¹) and lower kinetic energies (10²⁰–10²² erg), placing them closely in or near the picoflare energy regime, while eruptive events show higher speeds (131–775 km s⁻¹) and higher kinetic energies (10²²–10²⁴ erg), falling within the nanoflare regime. Furthermore, magnetic field extrapolations reveal a highly sheared arcade with greater twist and higher magnetic energy density in the eruptive event, compared to the less twisted configuration in the confined event. We infer that this sheared arcade configuration in the eruptive event creates favorable conditions for higher speeds and kinetic energies, unlike the less braided structure in the confined event. Our findings highlight the crucial role of the surrounding magnetic environment in regulating the energetics of nanoflare ejections in the solar atmosphere.

We present observations of an eruptive solar flare on 2016 January 6 that occurred behind the solar limb from the perspective of the Earth, but was well observed by the Solar-Terrestrial Relations Observatory (or STEREO) and the Solar Extreme Ultraviolet Monitor on NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Light curves showing the evolution of the flare’s irradiance as a function of time taken by MAVEN are well correlated with the brightness evolution of fan structures observed in the Project for On-Board Autonomy 2's Sun Watcher with Active Pixels and Image Processing (SWAP) 174 Å passband, suggesting that the radiance of structures near the flare site was influenced by emission from the flare. Because SWAP did not directly observe the flare itself, this event represents a rare opportunity to study the evolution of emission near a flare without the risk of instrumental scattered light contaminating the observations. We analyze this evolution and implement a simple model to explore the possibility that resonant excitation (RE, also known as resonant scattering) plays an important role in driving coronal extreme-ultraviolet (EUV) emission during flaring events. Our modeling shows that for a large flare, RE could increase emission from nearby structures by about 45%, consistent with our findings that the involved structures observed by SWAP increased in brightness by about 60% during the flare. We conclude that RE may play an important role in driving coronal EUV emission under certain circumstances and should be accounted for in models and emission-based analysis tools.