Esteban Sanchis Kilders

Emerging flux regions (EFRs) are key sites of magnetic flux transport and energy release in the solar atmosphere, often hosting arch filament systems (AFSs). We present high-resolution observations of an EFR obtained during the Sunrise III mission, combining spectropolarimetric measurements from the Tunable Magnetograph (TuMag) and Sunrise Chromospheric Infrared Spectro-Polarimeter (SCIP) with complementary observations from the Solar Dynamics Observatory (SDO). The data set provides a continuous view of an AFS over nearly 4 hr. Line-of-sight (LOS) velocities derived from the Mg I b ₂ line reveal three episodic plasma-flow events characterized by strong downflows reaching up to ∼17 km s ⁻¹ at the AFS footpoints and enhanced upflows near the loop tops. Although this pattern agrees with the classical emergence and draining scenario, the strongest upflows and downflows occur nearly simultaneously. Atmospheric Imaging Assembly (AIA) 304 and 171 Å observations reveal transient extreme-UV (EUV) brightenings in the surrounding emerging system; some occur during episodes of enhanced LOS velocities, while others do not, indicating that the temporal correspondence is not systematic. Multiline spectropolarimetric inversions reveal temperatures between ∼4000 and ∼10,000 K and a smooth variation of the magnetic field inclination along a representative AFS loop. Non-force-free-field extrapolations provide the large-scale magnetic context of the low-lying AFS loops and surrounding coronal structures. Together, the observations reveal a spatially and temporally complex evolution of the emerging system without establishing a direct causal connection between the local plasma-flow enhancements and the EUV brightenings.

Using high-resolution observations from the TuMag instrument aboard the Sunrise iii solar observatory balloon mission, we investigate solar vortices in the lower atmosphere. First, we identify vortices by extracting coherent dynamical patterns from intensity data using morphological analysis combined with spectral proper orthogonal decomposition applied to Mg I time series that probe the photosphere and lower chromosphere. We found that ∼8.5 × 10 ⁴ vortices may be present on the Sun at any given time, with an average lifetime of τ ≈ 27 minutes . To investigate vortex-mediated cross-layer coupling, we apply Granger causality (GC), which tests whether past fluctuations in one atmospheric layer carry statistically significant predictive power for future fluctuations in another, serving as a statistical proxy for directed dynamical coupling potentially associated with energy and momentum transfer. A pixel-to-pixel GC analysis reveals enhanced and spatially organized lower-atmospheric coupling within vortices, with statistically dominant photosphere-to-chromosphere influence in some locations and the reverse in others. This locally enhanced bidirectional spatial pattern of influence presents morphology consistent with the vortex-driven vertical Poynting flux distribution predicted by numerical simulations, suggesting that the coupling inferred from GC traces dynamical interactions associated with vortex-driven energy transport across atmospheric layers. On average, the directional asymmetry favors photosphere-to-chromosphere predictive coupling. Within vortex regions, past photospheric fluctuations provide ≈53% stronger predictive power for future chromospheric fluctuations than in nonvortex regions over a lag of 4.5 minutes. These results provide the first observational evidence of enhanced information transfer between atmospheric layers associated with solar vortices.

A part of the magnetic energy released during a flare is transported to the lower atmosphere. High-resolution observations show that flare ribbons, sites of energy deposition at the footpoints of flaring loops that appear bright in the chromosphere and transition region, are structured on small spatial scales on the order of 100 km. Based on idealized numerical models of flares it is suggested that the ribbon fine structures could originate from a tearing instability and the development of plasmoids in current sheets. Here we report on Fe i 5250.6 Å and Mg i b ₂ 5173 Å spectral observations of a solar flare from the Tunable Magnetograph on board the S unrise iii balloon-borne mission that reveal an intricate link between the flare ribbon structure and the ambient chromosphere. We identified uncombed chromospheric loops and nonflaring fine structures that are interspersed among brighter flare ribbon threads. These loops remain stable on timescales of minutes. Spectral lines from these regions show reduced emission or self-reversal in the line core compared with the immediately adjacent flare ribbons. We discuss the potential role of these structures in the onset of a flare. Furthermore, we suggest that irrespective of the complexities in the flaring current sheet, uncombed chromospheric loops and nonflaring fine structure might play a role in spatially modulating the flare energy deposition in the lower atmosphere.

S unrise iii is a stratospheric balloon-borne solar observatory with a 1 m diameter telescope and three postfocus instruments, along with an image stabilisation system, all within a protective gondola. It samples the lower solar atmosphere, from the solar surface to the middle chromosphere, at a resolution approaching 50 km on the Sun. S unrise iii flew successfully for 6.5 days suspended from a zero-pressure stratospheric balloon from northern Sweden to northwestern Canada in 2024 July, gathering around 200 TB of data. The present issue of the Astrophysical Journal Letters focuses on the first scientific results from the data collected during that flight. This Letter introduces this Focus Issue, providing a very brief overview of the capabilities of the instrumentation, the flight, and of the gathered data. Challenges for the measurements, data reduction, and interpretation are also briefly touched upon. The Letter ends with an overview of the first set of science results obtained from these data, as presented in the current Focus Issue.

The main contribution of this work is the demonstration of the positive influence of RC snubber circuits in a multiple-output buck-type converter beyond its original purpose. They not only improve the switching behaviour but also the frequency response and dynamic cross-regulation. Being only the low-power RC snubbers responsible for the overall converter stability and dynamic cross-regulation improvement, the use of smaller RC devices and low-power switching diodes is an additional benefit of this technique. The effect of using RC snubbers in the low-power outputs is similar to output inductor coupling.

Context. Images recorded with the Tunable Magnetograph (TuMag) instrument on board the S UNRISE III balloon observatory are affected by temporal contrast fluctuations. These variations are related to high-frequency vibrations (jitter) of the platform that cannot be entirely compensated by the image stabilization unit of the telescope. Jitter smooths out mid- to high-frequency details and degrades the contrast of images that are integrated over hundreds of milliseconds to achieve the signal-to-noise levels required by the instrument. The temporal variations of jitter hamper the reconstruction of the data and limit the accuracy of the instrument. Aims. We present a technique that allows us to infer and compensate temporal changes of the amplitude and direction of jitter from two images of the same scene, provided they are recorded close enough in time to prevent the scene from evolving significantly. Methods. We assess the performance of our method through a dynamical magnetohydrodynamical simulation of the solar scene that is degraded with diffraction effects, noise, and jitter. We evaluate the performance of the algorithm as a function of the jitter amplitude and as a function of the time gap between the two images. We finally apply it to a time series recorded by TuMag to sense and restore the temporal evolution of jitter on the images. Results. Our numerical experiments show that the algorithm is able to sense jitter with an accuracy better than 0.″005 (≲0.1 px) for images recorded less than 10 s apart and assuming a worst-case scenario with a low signal-to-noise ratio of 100 and induced rms jitter amplitudes as large as 0.″15 in the X and Y directions. When increasing the time interval to 30 s, the errors found are still below 0.″01. For the chosen TuMag series we find that the jitter rms amplitudes vary strongly within the range 0.″05–0.″15 (∼1–4 px) and are anticorrelated to the contrast of the recorded images. Correction of jitter improves the contrast of wavefront-reconstructed images by 2.5% in some cases and reduces the rms variation of contrast along the series by half.

This paper addresses the technical requirements and challenges encountered in the design and development of a customised power electronics board for a stratospheric balloon payload. This board includes power conversion and distribution to critical components (e.g., FPGAs and a ±4 kV power supply), as well as the pressurised enclosure designed to house these components along with other essential electronics. These systems were part of two scientific instruments onboard SUNRISE III, a high-altitude solar observatory launched in July 2024 from ESRANGE (Kiruna, Sweden), with a floating trajectory over the Arctic Circle. The SUNRISE III mission, based on a stratospheric balloon, was carried out by an international consortium of research institutions from Germany, Spain, Japan, and the United States, and in collaboration with NASA’s CSBF and the Swedish Space Corporation. Furthermore, this work presents telemetry data from the pressure sensing system of the electronic unit, as well as voltage and current measurements from the power electronics board outputs. These data were recorded during the floating phase of the mission, up to the balloon’s arrival in northern Canada after a successful week of scientific operations.