Peter H. Keys

Magnetic oscillations permeating the solar atmosphere can be altered by flares. This could be due to changes in the atmospheric magnetic waveguide, the thermodynamic stratification, or both. To investigate this, we examine oscillations in a magnetic pore crossed in part by the ribbon of a C8.2 flare, using observations from the S unrise Ultraviolet Spectropolarimeter and Imager (SUSI) aboard S unrise iii . We track the core intensities of eight spectral lines between 327–329 nm and show that oscillatory power in the 4.2–7.0 mHz range, measured around 30 minutes after the flare peak, exceeds the preevent value in all eight lines by factors of 1.60–8.71. Conversely, in the 7.0–11.5 mHz band, the postevent intensity power is lower—approximately 0.13–0.41 of the original power in seven of the observed lines. Line-center velocity measurements support the lower-frequency enhancement. This delayed, line-dependent shift toward the lower-frequency band is consistent with flare-induced changes in wave transmission, reflection, or resonant response, although thermodynamic and magnetic effects cannot yet be separated.

One of the first high-cadence chromospheric image sequences recorded with the recently commissioned Daniel K. Inouye Solar Telescope (DKIST) has revealed propagating arc-shaped bright fronts of a few hundred kilometers width. These bright fronts maintain their arc shape over up to one minute, travel with apparent horizontal speeds of ∼8 km s ⁻¹ , and originate from chromospheric bright grains seen at the center of the arc. We identify photospheric G -band bright points underneath the chromospheric bright grains, which are typically the signature of small-scale magnetic flux concentrations. The G -band bright points are found to interact with colocated vortices prior to the appearance of the chromospheric bright fronts. Images synthesized from three-dimensional magnetohydrodynamic simulations show a striking similarity with the discovered phenomenon and reveal that the arc-shaped bright fronts arise from essentially acoustic, weak shock fronts that propagate in the ambient medium, seemingly triggered by the vortex dynamics of the underlying magnetic flux concentration. In this work, we provide the first hints of a hitherto unknown magnetohydrodynamic process by which vortex-driven torsional Alfvén pulses couple to predominantly acoustic waves that steepen into shocks and dissipate their energies. The detected number density and frequency of these events are at least a factor 10 too small to be a major source of solar chromospheric heating but simulations show a seven times higher number density. We therefore expect to discover many more events with tailored narrow band observations.

Context. Three-minute (∼5 mHz) oscillations are a prominent signature of wave propagation in the solar chromosphere, but their measured power can vary substantially between full-disc observations and small, high-resolution fields of view. This variability suggests that the detectability of large-scale chromospheric oscillatory power may depend not only on wave excitation, but also on the magnetic topology through which the waves propagate. Aims. We investigate whether chromospheric magnetic canopy topology, in particular its lateral continuity and areal filling, modulates the field-of-view-averaged three-minute power measured in chromospheric diagnostics. Methods. We analysed high-resolution H α and Ca II 8542 Å spectral imaging from the Swedish 1-m Solar Telescope (SST) and compared canopy-poor quiet-Sun scenes with canopy-dominated active-region environments. These observations were complemented by radiative magnetohydrodynamic (MHD) Bifrost simulations representing canopy-poor and canopy-rich atmospheres. We computed field-of-view-averaged power spectra from pixel-wise fixed-wavelength intensities and bisector-derived line-of-sight velocities in the observations, and from synthetic intensities, vertical velocities, and temperature proxies in the simulations. We also quantified the relation between integrated 3–5 mHz excess power and canopy filling factor in both simulations and observations, using Helioseismic and Magnetic Imager (HMI)-based magnetic-field extrapolations for the latter. Results. In both observations and simulations, canopy-poor scenes show clear enhancements of field-of-view-averaged power in the 3–5 mHz band, whereas canopy-dominated scenes show strongly reduced measured power in the same frequency range. The trend is present in H α and Ca II 8542 Å intensity diagnostics and is supported by complementary velocity and temperature proxies. In both the simulations and SST observations, integrated 3–5 mHz excess power decreases with increasing canopy filling factor. Conclusions. Chromospheric field-of-view-averaged three-minute power is therefore a topology-weighted observable. Dense, laterally continuous magnetic canopies can strongly reduce the measured large-scale three-minute signature without requiring the absence of local wave activity. This effect provides a practical criterion for when chromospheric three-minute power should be recovered in spatially averaged diagnostics and should be considered when interpreting oscillation power as a proxy for atmospheric wave energy in the Sun and, more broadly, in magnetised cool-star atmospheres.

We present a multiline characterization of how oscillatory power is organized across distinct magnetic environments in an active region using seeing-free, stratospheric near-ultraviolet (near-UV) spectroscopy from the S unrise iii UV Spectropolarimeter and Imager (SUSI). A 2 hr time series of short raster scans in the line-rich 327–329 nm window samples along a single transect that contains the following regions: weak magnetic field surroundings, a plage, a sunspot, and a pore. From a set of 30 selected, relatively unblended absorption lines, we extract line-core Doppler velocity time series and compute Morlet-wavelet refined global spectra from which we form band-integrated power maps for three frequency bands (2–4, 4–6, and 6–12 mHz). The stacked, line-resolved maps reveal a clear environment-dependent redistribution of power: 2–4 mHz power is strongest in the weak-field/plage segments but is commonly suppressed in the umbra and pore cores, while 4–6 mHz and 6–12 mHz power becomes relatively enhanced in the strongest-field regions, with line-dependent behavior in the penumbra and plage. Across the line ensemble, this broad frequency structuring is coherent, but the detailed spatial distribution and relative band ranking are not identical from line to line—even among spectral lines with comparable effective formation depths—demonstrating clear line dependence. This novel result implies that single-line measurements may miss secondary components of the local wave spectrum because different lines weight coexisting perturbations and modes differently; therefore, the SUSI near-UV window provides a uniquely diagnostic-rich mapping of oscillations, offering leverage that is difficult to obtain with traditional one- or two-line approaches.

Bright points (BPs) are small-scale, dynamic features that are ubiquitous across the solar disc and are often associated with the underlying magnetic field. Using broadband photospheric images obtained with the Visible Broadband Imager at the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST), the properties of BPs have been analyzed with DKIST for the first time at the highest spatial resolutions achievable. BPs were observed to have an average lifetime of 95 ± 29 s and a mean transverse velocity of 1.60 ± 0.41 km s ⁻¹ . The BPs had a log-normal area distribution with a peak at 2300 km ² . Transverse velocities and lifetimes across the DKIST images were comparable and consistent with previous studies. The area distribution of the DKIST data peaked in areas significantly lower than those from the literature. This was explored further and was observed to be due to an overestimation of BP areas due to the merging of close features when the spatial resolution is reduced, in tandem with possible oversplitting of features in the DKIST images. Furthermore, the effect of variable seeing in the data was determined. This showed that the average spatial resolution of the data was around 0 . ″ 034 ± 0 . ″ 007 , in comparison to the theoretical diffraction limit of 0 . ″ 022 . Accounting for the influence of seeing, the peak of the area distribution of BPs in the DKIST data was estimated as 4800 km ² , which is still significantly lower than previously observed.

The Sunspot Solar Observatory Data Archive (SSODA) stores data acquired with the suite of instruments at the Richard B. Dunn Solar Telescope (DST) from February 2018 to the present. The instrumentation at the DST continues to provide high cadence imaging, spectroscopy, and polarimetry of the solar photosphere and chromosphere across a wavelength range from 3500 Å to 11,000 Å. At the time of writing, the archive contains approximately 374 TiB of data across more than 520 observing days (starting on February 1, 2018). These numbers are approximate as the DST remains operational, and is actively adding new data to the archive. The SSODA includes both raw and calibrated data. A subset of the archive contains the results of photospheric and chromospheric spectropolarimetric inversions using the Hazel-2.0 code to obtain maps of magnetic fields, temperatures, and velocity flows. The SSODA represents a unique resource for the investigation of plasma processes throughout the solar atmosphere, the origin of space weather events, and the properties of active regions throughout the rise of Solar Cycle 25.

The morphology of circular polarization profiles from solar spectropolarimetric observations encodes information about the magnetic field strength, inclination, and line-of-sight velocity gradients. Previous studies used manual methods or unsupervised machine learning (ML) to classify the shapes of circular polarization profiles. We trained a multilayer perceptron comparing classifications with unsupervised ML. The method was tested on quiet Sun data sets from Daniel K. Inouye Solar Telescope (DKIST), Hinode, and GREGOR, as well as simulations of granulation and a sunspot. We achieve validation metrics typically close to or above 90%. We also present the first statistical analysis of quiet Sun DKIST/ViSP data using inversions and our supervised classifier. We demonstrate that classifications with unsupervised ML alone can introduce systemic errors that could compromise statistical comparisons. DKIST and Hinode classifications in the quiet Sun are similar, despite our modeling indicating spatial resolution differences should alter the shapes of circular polarization signals. Asymmetrical (symmetrical) profiles are less (more) common in GREGOR than DKIST or Hinode data, consistent with narrower response functions in the 1564.85 nm line. Single-lobed profiles are extremely rare in GREGOR data. In the sunspot simulation, the 630.25 nm line produces “double” profiles in the penumbra, likely a manifestation of magneto-optical effects in horizontal fields; these are rarer in the 1564.85 nm line. We find the 1564.85 nm line detects more reverse polarity magnetic fields in the penumbra, in contradiction to observations. We detect mixed-polarity profiles in nearly one fifth of the penumbra. Supervised ML robustly classifies solar spectropolarimetric data, enabling detailed statistical analyses of magnetic fields.

Context. Magnetic bright points (MBPs) are one of the smallest manifestations of the magnetic field in the solar atmosphere and are observed to extend from the photosphere up to the chromosphere. As such, they represent an excellent feature to use in searches for types of magnetohydrodynamic (MHD) waves and mode coupling in the solar atmosphere. Aims. In this work, we aim to study wave propagation in the lower solar atmosphere by comparing intensity oscillations in the photosphere with the chromosphere via a search for possible mode coupling, in order to establish the importance of these types of waves in the solar atmosphere, and their contribution to heating the chromosphere. Methods. These observations were conducted in July 2011 with the Rapid Oscillations of the Solar Atmosphere (ROSA) and the Hydrogen-Alpha Rapid Dynamics Camera (HARDCam) instruments at the Dunn Solar Telescope. Observations with good seeing were made in the G-band and Hα wave bands. Speckle reconstruction and several post facto techniques were applied to return science-ready images. The spatial sampling of the images was 0.069″/pixel (50 km/pixel). We used wavelet analysis to identify traveling MHD waves and derive frequencies in the different bandpasses. We isolated a large sample of MBPs using an automated tracking algorithm throughout our observations. Two dozen of the brightest MBPs were selected from the sample for further study. Results. We find oscillations in the G-band MBPs, with frequencies between 1.5 and 3.6 mHz. Corresponding MBPs in the lower solar chromosphere observed in Hα show a frequency range of 1.4–4.3 mHz. In about 38% of the MBPs, the ratio of Hα to G-band frequencies was near two. Thus, these oscillations show a form of mode coupling where the transverse waves in the photosphere are converted into longitudinal waves in the chromosphere. The phases of the Hα and G-band light curves show strong positive and negative correlations only 21% and 12% of the time, respectively. Conclusions. From simple estimates we find an energy flux of ≈45 × 10³ W m⁻² and show that the energy flowing through MBPs is enough to heat the chromosphere, although higher-resolution data are needed to explore this contribution further. Regardless, mode coupling is important in helping us understand the types of MHD waves in the lower solar atmosphere and the overall energy budget.