Achim Gandorfer

The near-ultraviolet part of the solar spectrum is densely crowded with spectral lines. Scattered among them are neutral iron lines with bell-shaped intensity profiles forming as high as the mid-chromosphere. Based on 1D model atmospheres, we predicted in our previous paper that these lines have unique multilobed Stokes V profiles even in the absence of gradients in magnetic field inclination or in line-of-sight velocity. The Sunrise Ultraviolet Spectropolarimeter and Imager (SUSI) instrument on board the Sunrise iii flight captured high spectral and spatial resolution observations in one such strong chromospheric Fe i line at 407.17 nm, in and around a sunspot. In these observations, these multilobed V profiles are best seen in the inner parts of the penumbra, where the Stokes V signal is strong and the Stokes I line shape displays the characteristic flattening of the inner wing along with a steep line core. By applying the weak field approximation (WFA) separately to the line core and wings, we infer line-of-sight magnetic field strengths ( B _LOS ) at different heights in the atmosphere. We find differences between the inferred B _LOS obtained from the line core and wing of up to 700 G. Despite the blend line in the blue wing and the relatively weak Stokes V signals, we show that it is still possible to qualitatively infer B _LOS simultaneously at different heights in the atmosphere using the WFA on the Fe i 407.17 nm line.

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.

We present off-limb spectroscopy using low-stray-light data from the Sunrise Spectropolarimeter and Imager (SUSI) on board the S unrise iii stratospheric solar observatory. A spatial scan with SUSI’s slit almost parallel to the local limb reached from within the solar disk to 6.5 Mm off-limb. The wavelength range spanned from 407.6 to 410.25 nm. We detected a total of 174 spectral lines in emission off-limb, a 2.5-fold increase over previous reports. Surprisingly, 122 of these lines begin to appear in emission already on the disk, although close to the limb. In addition, one-fifth of relatively prominent emission lines are due to rare-earth and heavy elements and molecules, where the absorption lines of these transitions are typically weak on-disc.

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.

We present spectropolarimetric observations of an on-disk condensation event obtained with Sunrise/SCIP in the Ca ii 854.2 nm line. The event occurred during the coalescence of two pores of the same magnetic polarity, accompanied by coronal brightenings that indicate magnetic activity in the loop system before the appearance of the condensations. We identify the material through red-wing absorption signatures and infer its properties using a two-stage approach that combines spectropolarimetric inversions and Doppler-velocity fitting. Good fits were obtained for about 1400 profiles (∼60% of the detected pixels), yielding chromospheric temperatures (5900–9100 K, mode near 7400 K) and line-of-sight velocities of 5–45 km s ⁻¹ (mode near 14 km s ⁻¹ ). We then apply the weak-field approximation in narrow spectral windows centered on the inferred Doppler shifts, obtaining B _LoS values from approximately −100 to −900 G in the coronal rain material. To interpret the large spatial variation of B _LoS , we compare the observations with a force-free magnetic field extrapolation and find a loop whose projected B _z variation reproduces the observed trend along the traced path. The inferred loop geometry also yields free-fall speeds consistent with the measured velocities. These results show that high-resolution spectropolarimetry of on-disk coronal rain can provide constraints on the thermodynamic and magnetic properties of cool plasma in coronal loops. The comparison with the extrapolated field also suggests that the observed B _LoS trend is compatible with a plausible loop geometry.

Magnetic fields in the solar atmosphere are expected to expand with height, forming magnetic canopies that couple the photosphere and chromosphere. Except for sunspots, direct measurements of this expansion remain scarce because they require simultaneous magnetic diagnostics over a broad range of atmospheric heights. We analyze four consecutive high-resolution spectropolarimetric raster scans of an emerging flux region observed with the Sunrise III/SCIP instrument. Simultaneous inversions of five photospheric Fe i lines and two chromospheric Ca ii lines provide a quasi-continuous reconstruction of the magnetic field from the deep photosphere to the lower chromosphere. We apply a constant-flux method that follows the same magnetic flux through different atmospheric layers to quantify magnetic expansion. All three pores analyzed exhibit an overall increase in magnetic area with height, approximately doubling their cross section between the lower photosphere and the highest atmospheric layers sampled by the inversions. The expansion remains broadly stable throughout the 48 minute observing sequence. We further characterize the expansion with a quadratic parameterization and investigate its relation to pore properties. The three pores exhibit similar core magnetic field strengths but different expansion behaviors, indicating that the magnetic core strength alone does not determine the expansion. However, the present sample is too small to establish whether these differences are related to the thermodynamic or magnetic properties of the pores and their surroundings. These results demonstrate the potential of simultaneous multiline inversions for investigating the three-dimensional magnetic topology of solar magnetic structures and provide the first direct measurements of the height-dependent magnetic expansion of solar pores.

Flares are caused by an abrupt release of magnetic energy in the solar atmosphere. Plasma heated to well over 10 MK filling the postflare corona originates from a rapid heating and ablation of the cooler chromospheric material. This chromospheric evaporation is thought to be facilitated primarily by nonthermal electrons impinging onto the lower atmosphere. Questions on when and where in the chromosphere these upflows originate, however, are not fully resolved. Here we report on unprecedented high-resolution observations of an M-class flare recorded by the Sunrise Ultraviolet Spectropolarimeter and Imager on board the balloon-borne Sunrise iii observatory that reveal highly structured upflows on spatial scales of ∼100 km originating deep in the chromosphere. The flows even precede the onset of nonthermal electrons by about 10 minutes and last through the impulsive phase of the flare. Our observations shed new light on the lower atmospheric heating and mass circulation in flares that are challenging to reconcile with the standard solar flare model.

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.

We present high-resolution multiline spectropolarimetric observations of a quiet-Sun network element obtained with the S unrise iii Chromospheric Infrared SpectroPolarimeter. The observations combine photospheric, upper-photospheric, and chromospheric diagnostics at a spatial resolution and polarimetric sensitivity that allow the transverse magnetic structure of the network boundary to be examined directly. We find that the strongest linear polarization is concentrated in a narrow ridge around the edge of the magnetic element, cospatial with enhanced transverse magnetic field inferred from multiline inversions. The magnetic azimuth exhibits a coherent, predominantly radial organization around a more vertical core, consistent with an expanding magnetic canopy. An azimuth proxy derived directly from the observed Fe i and K i linear polarization reproduces the same large-scale organization, showing that this structure is encoded in the Stokes profiles rather than imposed by the inversion. Response functions and a MURaM-based forward-synthesis test indicate that the Fe i 8468 Å linear polarization is sensitive to magnetic azimuth in the upper photosphere, with the closest proxy agreement occurring near log τ ≈ − 3 . We find no evidence for strong azimuthal shear between the Fe- and K-sensitive diagnostics. At the network boundary, we also identify localized parasitic-polarity patches associated with complex, multilobed Stokes V profiles and one case in which the Stokes V polarity reverses between photospheric Fe i and chromospheric Ca ii lines. These results demonstrate that quiet-Sun network boundaries contain organized upper-photospheric canopy fields together with a small-scale mixed-polarity structure, providing new constraints on the three-dimensional magnetic structure of network elements.

The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) instrument on board the balloon-borne S unrise iii observatory provided new high-resolution observations of the solar chromosphere in the Ca ii λ 854.2 nm line. The Stokes V signal in magnetic network regions was found to show fine-structured details, which suggests the magnetic field above the network elements does not simply expand as a unipolar feature but displays opposite-polarity intrusions (OPIs). These features appear as elongated structures in Stokes V observations. In this work, we demonstrate that such features appear ubiquitously in a numerical simulation of the solar chromosphere. We use a simulation that is computed with the recently developed chromospheric extension of MURaM (MURaM-ChE) and resembles an enhanced network region. We find that OPIs appear ubiquitously in the vertical component of the magnetic field at around 1 Mm above the surface and are visible in the synthetic Stokes V signal of the Ca ii λ 854.2 nm line. The structures have lengths of ≈2–7 Mm and widths of approximately 1 Mm. The magnetic field configurations associated with the OPI features appear to belong to twisted flux ropes and are visible for most of the time in the presented 21 minutes time series. Our results show that the magnetic structure of the chromosphere is more complex than previously thought, with even seemingly simple flux tubes showing embedded twisted fields pointing in the opposite direction. This may help in explaining new high-resolution observations from the S unrise iii mission.