Yoshinori Suematsu

Acoustic waves propagate into the chromosphere, contributing to energy transport and their dynamics. Their upward propagation is restricted to frequencies above the acoustic cutoff frequency. The magnetic field configuration plays a key role in determining whether acoustic waves can propagate upward because the cutoff frequency is reduced in regions where the field is inclined with respect to gravity, forming so-called magnetoacoustic portals. Previous studies linked magnetic fields and oscillations in quiet regions, but these analyses were based on photospheric magnetic field information, leaving chromospheric structure unconstrained. This study investigates the coupling between acoustic waves and magnetic topology using photospheric and, for the first time, chromospheric spectropolarimetry in a quiet region, obtained with the Sunrise Chromospheric Infrared SpectroPolarimeter (SCIP) aboard the Sunrise iii balloon-borne solar observatory launched in 2024. The SCIP sit-and-stare observations sampled magnetic features in which the line-of-sight field strength exhibits multiple sharp spatial peaks in the photosphere while becoming broader and weaker at two heights in the chromosphere, indicating expanding fluxtubes. The chromospheric velocity field in these fluxtubes exhibits strong 5 minute oscillations, while the surrounding regions show weak 3 minute oscillations. In these fluxtubes, sawtooth temporal velocity variations are associated with intensity enhancements, suggesting steepened shocks. Fluxtubes with low-frequency oscillations are identified not only in network regions but also in weak internetwork regions. These results provide observational evidence that fluxtubes expanding into the chromosphere act as magnetoacoustic portals, in both network and internetwork regions, allowing low-frequency waves to propagate upward and driving chromospheric dynamics via shocks.

The balloon-borne stratospheric solar observatory S unrise iii successfully completed 6.5 days of observations in 2024 July. One of its focal-plane instruments, the Sunrise Chromospheric Infrared spectroPolarimeter (SCIP), is a slit-scanning spectropolarimeter that simultaneously measures full Stokes profiles of multiple spectral lines in the 850 nm and 770 nm bands. SCIP obtained an unprecedented data set of a quiet-Sun region near the disk center, covering a 58″ × 58″ field of view. With an integration time of 10 s per slit position, the scan was completed in 107 minutes without interruption, achieving remarkably stable polarimetric precision of 0.03%–0.04% (1 σ ) of the continuum level. The multiwavelength SCIP observations reveal that the chromospheric line-of-sight (LOS) magnetic field exhibits thread-like elongated structures over the internetwork regions, with no obvious photospheric counterpart directly below. These threads are typically narrower than 1″ and are embedded within the canopy fields extending from the network regions. Their LOS field strengths derived from the weak-field approximation are typically 10–20 G weaker than the surrounding canopy. In particularly clear cases, the magnetic polarity of the threads is opposite to that of the adjacent canopy. These findings suggest that the canopy field is not simply an expanding structure originating from network regions, but instead has a complex three-dimensional configuration containing numerous localized substructures. These observations provide new constraints on the quiet-Sun magnetic topology from the photosphere to the chromosphere.

Ellerman bombs (EBs) are widely recognized as photospheric and chromospheric signatures of magnetic reconnection. However, the 3D magnetic topology has remained elusive due to the lack of seamless height coverage in observations. Here, we present initial results from the S unrise iii /Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) observations of an emerging flux region. Exploiting the seeing-free, high-spatial-resolution observations provided by the 1 m balloon-borne telescope, SCIP achieved seamless multiline spectropolarimetry from the photosphere to the lower chromosphere. We analyzed the multiline Stokes profiles of the photospheric Fe i and K i lines and the chromospheric Ca ii lines, and applied the weak field approximation to the K i and Ca ii lines to reconstruct the 3D magnetic field structure. The blue- and red-wing brightenings of the Ca ii 8542 Å line appear at spatially offset locations, indicating bidirectional reconnection flows. The reconstructed 3D magnetic field reveals that the opposite-polarity field structure reaches different heights in the two events analyzed. In one event, it is confined to the lower layers and is absent at the formation height of the Ca ii 8542 Å core, which shows no intensity enhancement, whereas in the other event it extends up to the Ca ii 8542 Å core formation height, where enhanced line-core intensity is also observed. We interpret this as the reconnection current sheet reaching different altitudes. These results demonstrate that SCIP has successfully resolved the 3D structure of EBs, distinguishing magnetic reconnection events occurring at different atmospheric heights.

Understanding the magnetic field structure of spicules is essential for developing their formation models, which are important for understanding the mass transport to the corona and coronal heating. We report the spatial distribution of spicule magnetic fields from spectropolarimetric observations with Sunrise iii /SCIP, which provides high spatial resolution and high polarization sensitivity under seeing-free conditions. We observed the solar limb above a quiet region with SCIP and detected clear Stokes V signals in the Ca II 8542 Å line from off-limb spicules. We applied the weak field approximation to estimate the line-of-sight (LOS) component of the magnetic field ( B _LOS ) of spicules. We find that B _LOS ranges up to 20 G, nearly independent of height, in the region up to 3″ from the limb, whereas the distribution broadens to 40 G at 3″–6″ from the limb. The Stokes I profiles averaged at increasing distance from the limb reveal a transition from a double-peaked shape to a single-peaked one at around 3″ from the limb. Because we can see a dense forest of spicules overlapping each other above the limb, the observational results suggest that the B _LOS depends on how deeply the Ca II line can penetrate the spicule forest along the LOS. At heights with double-peaked profiles, the estimated B _LOS represents the magnetic field of a foreground spicule. In contrast, at heights with single-peaked profiles, it reflects contributions from a number of prominent, tall, inclined spicules, leading to more dispersed B _LOS values.

Deciphering the physical properties of flares is crucial for understanding the nature of one of the most energetic events on the Sun. We analyze high spatial and spectral resolution observations of a C-class flare, focusing on a complex light bridge in the active region. The observations show Stokes profiles with opposite Doppler shifts and asymmetries between photospheric and chromospheric spectral lines, and Ca ii infrared spectral lines in emission, tracing areas of extreme atmospheric heating. Inversion results are consistent with these spectral features, showing regions of opposite-sign plasma flows between the photosphere and chromosphere, adjacent to areas with extreme chromospheric temperatures. The latter areas show relatively weak line-of-sight velocities despite the intense heating. The magnetic field configuration shows abrupt changes with height in the regions with opposite-sign flows, while remaining nearly constant with height in the areas of extreme heating. These findings point to a scenario of small-scale magnetic reconnection in the photosphere, suggesting a flare triggering mechanism based on an avalanche of many small reconnection events.

We report high-spatial-resolution spectropolarimetric observations spatially associated with a solar filament, obtained with the Sunrise Chromospheric Infrared Spectro-Polarimeter (SCIP) on board the Sunrise iii balloon-borne solar observatory on 2024 July 15. The observed filament was located near the solar disk center, adjacent to an active region, and remained quiescent for at least 2 hr during the observing period. SCIP recorded full Stokes profiles in the Ca ii 8542 Å line, revealing clear signatures of linear polarization produced by the transverse Zeeman effect. The detected linear polarization signals within the filament region exceeded the 2σ noise level and exhibited a characteristic Zeeman double-lobe spectral shape that distinguishes them from polarization due to scattering. The magnetic field strength derived using the weak field approximation is approximately −80 G along the line of sight and 300–500 G in the transverse direction. These values likely reflect the magnetic properties of the filament and its supporting chromospheric environment. The orientation of the magnetic field vector is nearly parallel to the filament axis in its northeastern portion, while the southeastern part of the filament extends outside the field of view. To our knowledge, this is the first unambiguous detection of linear polarization associated with a solar filament with the Ca ii 8542 Å line. Our results open a new diagnostic window to the vector magnetic structure of solar filaments in the lower chromosphere, complementing existing He i based diagnostics that probe the upper chromosphere.

Whitepaper #020 in the Decadal Survey for Solar and Space Physics (Heliophysics) 2024-2033. Main topics: space weather applications; basic research. Additional topics: space weather research/applications/operations pipeline; ground-based missions/projects; solar physics.

We describe newly developed voltage-tunable lithium-niobate (LiNbO3) Fabry-Perot etalons for solar near-infrared filtergraph. Two etalons were fabricated for tandem use: One etalon is 0.9 mm thick and the other is 1.2 mm thick, optimized in ordinary ray transmission for both He I 1083.035 nm and magnetic sensitive Fe I 1564.85 nm lines. The etalons are Y-cut lithium-niobate wafers coated with highly reflective and conductive (ITO) layers. We examined optical and voltage-tunable properties of the etalons using the horizontal spectrograph of the Domeless Solar Telescope at Hida Observatory, Kyoto University. Some solar observations with tandem etalons were also ran and their good imaging quality was demonstrated. Some results from the measurements are reported.