Christopher Samuel Moore

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.

On 2024 April 17, the third successful Hi-C sounding rocket flight, Hi-C Flare, recorded coronal images in Fe XXI 129 Å emission from 11 MK plasma during the postmaximum phase of an M1.6-class solar flare, achieving unprecedented spatial (∼300 km) and temporal (1.3 s) resolutions. The flare started at 21:55 UT, peaked at 22:08 UT, and lasted ∼40 minutes. Hi-C observed for over 5 minutes (22:15:45–22:21:25), starting roughly 8 minutes after flare maximum. A sudden compact bright burst—875 ± 25 km wide, lasting 90 ± 1.3 s, exhibiting a proper motion of ∼ 50 km s ⁻¹ , and splitting into two toward the end—occurs near the foot of some postflare loops. Its size and brightness are reminiscent of flare-ribbon kernels during a flare’s rapid rise phase, kernels marking sites of sudden heating and hot plasma upflow, making its occurrence during the late phase surprising. Such isolated brightenings in a flare’s postmaximum phase are rare and have not been previously reported. The kernel was detected in all Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly channels. Its 1600 Å light curve peaked ∼50 s earlier than its 131 Å light curve, similar to that of flare-ribbon kernels, albeit with a smaller delay of ∼25 s, during the impulsive phase of the flare. In SDO/Helioseismic Magnetic Imager magnetograms, the kernel sits in unipolar positive magnetic flux near an embedded clump of negative flux. Although localized magnetic reconnection within the kernel (a microflare) cannot be ruled out for its cause, the observations favor the localized brightening being an isolated, exceptionally late flare-ribbon kernel, resulting from an exceptionally late burst of the flare’s coronal reconnection.

We investigate the thermal properties of a solar flare by the observations of the soft X-ray Telescope on board Hinode and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. Our analysis reveals a tenuous but hot plasma cloud located above the flare loops. The flare loops and plasma cloud exhibit independent temperature profiles as a function of time, implying that different heating mechanisms are present in these structures. We interpret the plasma cloud as an eruptive filament directly heated in the corona via magnetic reconnection that occurs when a rising filament interacts with this eruptive filament. Previous disk-integrated solar soft X-ray spectral measurements of this flare using the Miniature X-ray Solar Spectrometer CubeSat-1 (MinXSS-1) inferred coronal abundances at the flare peak. However, MinXSS synthetic spectra from AIA observations show that the plasma cloud is too tenuous to be detected in MinXSS-1; thus, the coronal abundances of low first ionization potential elements must be in emission from the flare loops. Furthermore, we demonstrate the nonnegligible differences in differential emission measures between coronal and photospheric abundance models. These results highlight the importance of instruments capable of simultaneous spectral and spatial diagnostics during large-scale solar events. Such coordinated measurements would enable more accurate thermal and compositional analyses and deeper insight into the underlying physical mechanisms.

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.

Solar flares are complex phenomena emitting all types of electromagnetic radiation and accelerating particles on timescales of minutes, converting magnetic energy to thermal, radiative, and kinetic energy through magnetic reconnections. As a result, local plasma can be heated to temperatures in excess of 20 MK. During the soft X-ray (SXR) solar flare peak, the elemental abundance of low first ionization potential elements are typically observed to be depleted from coronal values. We explored the abundance variations using disk-integrated solar spectra from the Miniature X-ray Solar Spectrometer CubeSat-1 (MinXSS-1). MinXSS-1 is sensitive to the 1–12 keV energy range with an effective 0.25 keV FWHM resolution at 5.9 keV. During the year-long mission of MinXSS-1, between 2016 May and 2017 May, 21 flares with intermittent data downlinks were observed ranging from C to M class. We examine the time evolution of temperature, volume emission measure, and elemental abundances of Fe, Ca, Si, S, and Ar with CHIANTI spectral models near the peak SXR emission times observed in the MinXSS-1 data. We determined the average absolute abundance of A(Fe) = 7.81, A(Ca) = 6.84, A(S) = 7.28, A(Si) = 7.90, and A(Ar) = 6.56. These abundances are depleted from coronal values during the SXR peak compared to nonflaring times. The elemental abundance values that are depleted from their coronal values are consistent with the process of chromospheric evaporation, in which the lower atmospheric plasma fills the coronal loops.

Three generations of the Miniature X-ray Solar Spectrometer (MinXSS) have flown on small satellites with the goal “to explore the energy distribution of soft X-ray (SXR) emissions from the quiescent Sun, active regions, and during solar flares, and to model the impact on Earth’s ionosphere and thermosphere.” The primary science instrument is the Amptek X123 X-ray spectrometer that has improved with each generation of the MinXSS experiment. This third-generation MinXSS-3 has a higher energy resolution and larger effective area than its predecessors and is also known as the Dual-zone Aperture X-ray Solar Spectrometer (DAXSS). It was launched on the INSPIRESat-1 satellite on 2022 February 14, and INSPIRESat-1 has successfully completed its 6 month prime mission. The INSPIRESat-1 is in a dawn–dusk, Sun-synchronous orbit and therefore has had 24 hr coverage of the Sun during most of its mission so far. The rise of Solar Cycle 25 has been observed by DAXSS. This paper introduces the INSPIRESat-1 DAXSS solar SXR observations, and we focus the science results here on a solar occultation experiment and multiple flares on 2022 April 24. One key flare result is that the reduction of elemental abundances appears greatest during the flare impulsive phase, thus highlighting the important role of chromospheric evaporation during flares to inject warmer plasma into the coronal loops. Furthermore, these results are suggestive that the amount of chromospheric evaporation is related to flare temperature and intensity.

Whitepaper #129 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: basic research. Additional topics: solar physics.

Whitepaper #268 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: infrastructure/workforce/other programmatic. Additional topics: state of the profession; research tools and infrastructure.

Whitepaper #364 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: basic research. Additional topics: solar physics; space-based missions/projects; user-need-driven basic space weather research.

Whitepaper #181 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: basic research. Additional topics: solar physics.