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The plasma composition of the solar corona is different from that of the solar photosphere. Elements that have a low first ionization potential (FIP) are preferentially transported to the corona and therefore show enhanced abundances in the corona compared to the photosphere. The level of enhancement is measured using the FIP bias parameter. In this work, we use data from the EUV Imaging Spectrometer on Hinode to study the plasma composition in an active region following an episode of significant new flux emergence into the preexisting magnetic environment of the active region. We use two FIP bias diagnostics: Si x 258.375 Å/S x 264.233 Å (temperature of approximately 1.5 MK) and Ca xiv 193.874 Å/Ar xiv 194.396 Å (temperature of approximately 4 MK). We observe slightly higher FIP bias values with the Ca/Ar diagnostic than Si/S in the newly emerging loops, and this pattern is much stronger in the preexisting loops (those that had been formed before the flux emergence). This result can be interpreted in the context of the ponderomotive force model, which proposes that the plasma fractionation is generally driven by Alfvén waves. Model simulations predict this difference between diagnostics using simple assumptions about the wave properties, particularly that the fractionation is driven by resonant/nonresonant waves in the emerging/preexisting loops. We propose that this results in the different fractionation patterns observed in these two sets of loops. [ABSTRACT FROM AUTHOR]

From 2022 March 18 to 21, NOAA Active Region (AR) 12967 was tracked simultaneously by Solar Orbiter at 0.35 au and Hinode/EIS at Earth. During this period, strong blueshifted plasma upflows were observed along a thin, dark corridor of open magnetic field originating at the AR's leading polarity and continuing toward the southern extension of the northern polar coronal hole. A potential field source surface model shows large lateral expansion of the open magnetic field along the corridor. Squashing factor Q -maps of the large-scale topology further confirm super-radial expansion in support of the S-web theory for the slow wind. The thin corridor of upflows is identified as the source region of a slow solar wind stream characterized by ∼300 km s−1 velocities, low proton temperatures of ∼5 eV, extremely high density >100 cm−3, and a short interval of moderate Alfvénicity accompanied by switchback events. When the connectivity changes from the corridor to the eastern side of the AR, the in situ plasma parameters of the slow solar wind indicate a distinctly different source region. These observations provide strong evidence that the narrow open-field corridors, forming part of the S-web, produce some extreme properties in their associated solar wind streams. [ABSTRACT FROM AUTHOR]

In this study, we investigate the spatial distribution of highly varying plasma composition around one of the largest sunspots of solar cycle 24. Observations of the photosphere, chromosphere, and corona are brought together with magnetic field modeling of the sunspot in order to probe the conditions that regulate the degree of plasma fractionation within loop populations of differing connectivities. We find that, in the coronal magnetic field above the sunspot umbra, the plasma has photospheric composition. Coronal loops rooted in the penumbra contain fractionated plasma, with the highest levels observed in the loops that connect within the active region. Tracing field lines from regions of fractionated plasma in the corona to locations of Alfvénic fluctuations detected in the chromosphere shows that they are magnetically linked. These results indicate a connection between sunspot chromospheric activity and observable changes in coronal plasma composition. [ABSTRACT FROM AUTHOR]

The Parker Solar Probe mission has shown the ubiquitous presence of strong magnetic field deflections, namely switchbacks, during its first perihelion where it was embedded in a highly Alfvénic slow stream. Here, we study the turbulent magnetic fluctuations around ion scales in three intervals characterized by a different switchback activity, identified by the behavior of the magnetic field radial component, Br. Quiet (Br does not show significant fluctuations), weakly disturbed (Br has strong fluctuations but no reversals), and highly disturbed (Br has full reversals) periods also show different behavior for ion quantities. However, the spectral analysis shows that each stream is characterized by the typical Kolmogorov/Kraichnan power law in the inertial range, followed by a break around the characteristic ion scales. This frequency range is characterized by strong intermittent activity, with the presence of noncompressive coherent events, such as current sheets, vortex-like structures, and wave packets identified as ion cyclotron modes. Although all these events have been detected in the three periods, they have different influences in each of them. Current sheets are dominant in the highly disturbed period, wave packets are the most common in the quiet interval; while, in the weakly disturbed period, a mixture of vortices and wave packets is observed. This work provides an insight into the heating problem in collisionless plasmas, fitting in the context of the new solar missions, and, especially for Solar Orbiter, which will allow an accurate magnetic connectivity analysis to link the presence of different intermittent events to the source region. [ABSTRACT FROM AUTHOR]

The formation of shocks within the solar atmosphere remains one of the few observable signatures of energy dissipation arising from the plethora of magnetohydrodynamic waves generated close to the solar surface. Active region observations offer exceptional views of wave behavior and its impact on the surrounding atmosphere. The stratified plasma gradients present in the lower solar atmosphere allow for the potential formation of many theorized shock phenomena. In this study, using chromospheric Ca ii λ8542 line spectropolarimetric data of a large sunspot, we examine fluctuations in the plasma parameters in the aftermath of powerful shock events that demonstrate polarimetric reversals during their evolution. Modern inversion techniques are employed to uncover perturbations in the temperatures, line-of-sight velocities, and vector magnetic fields occurring across a range of optical depths synonymous with the shock formation. Classification of these nonlinear signatures is carried out by comparing the observationally derived slow, fast, and Alfvén shock solutions with the theoretical Rankine–Hugoniot relations. Employing over 200,000 independent measurements, we reveal that the Alfvén (intermediate) shock solution provides the closest match between theory and observations at optical depths of , consistent with a geometric height at the boundary between the upper photosphere and lower chromosphere. This work uncovers first-time evidence of the manifestation of chromospheric intermediate shocks in sunspot umbrae, providing a new method for the potential thermalization of wave energy in a range of magnetic structures, including pores, magnetic flux ropes, and magnetic bright points. [ABSTRACT FROM AUTHOR]

Penumbral transient brightening events have been attributed to magnetic reconnection episodes occurring in the low corona. We investigated the trigger mechanism of these events in active region NOAA 12546 by using multiwavelength observations obtained with the Interferometric Bidimensional Spectrometer, by the Solar Dynamics Observatory, the Interface Region Imaging Spectrograph, and the Hinode satellites. We focused on the evolution of an area of the penumbra adjacent to two small-scale emerging flux regions (EFRs), which manifested three brightening events detected from the chromosphere to the corona. Two of these events correspond to B-class flares. The same region showed short-lived moving magnetic features (MMFs) that streamed out from the penumbra. In the photosphere, the EFRs led to small-scale penumbral changes associated with a counter-Evershed flow and to a reconfiguration of the magnetic fields in the moat. The brightening events had one of the footpoints embedded in the penumbra and seemed to result from the distinctive interplay between the preexisting penumbral fields, MMFs, and the EFRs. The IRIS spectra measured therein reveal enhanced temperature and asymmetries in spectral lines, suggestive of event triggering at different heights in the atmosphere. Specifically, the blue asymmetry noted in C ii and Mg ii h&k lines suggests the occurrence of chromospheric evaporation at the footpoint located in the penumbra as a consequence of the magnetic reconnection process at higher atmospheric heights. [ABSTRACT FROM AUTHOR]

We report observations of small-scale swirls seen in the solar chromosphere. They are typically 2 Mm in diameter and last around 10 minutes. Using spectropolarimetric observations obtained by the CRisp Imaging Spectro-Polarimeter at the Swedish 1 m Solar Telescope, we identify and study a set of swirls in chromospheric Ca ii 8542 Å and Hα lines as well as in the photospheric Fe i line. We have three main areas of focus. First, we compare the appearance, morphology, dynamics, and associated plasma parameters between the Ca ii and Hα channels. Rotation and expansion of the chromospheric swirl pattern are explored using polar plots. Second, we explore the connection to underlying photospheric magnetic concentration (MC) dynamics. MCs are tracked using the SWAMIS tracking code. The swirl center and MC remain cospatial and share similar periods of rotation. Third, we elucidate the role swirls play in modifying chromospheric acoustic oscillations and found a temporary reduction in wave period during swirls. We use cross-correlation wavelets to examine the change in period and phase relations between different wavelengths. The physical picture that emerges is that a swirl is a flux tube that extends above an MC in a downdraft region in an intergranular lane. The rotational motion of the MC matches the chromospheric signatures. We could not determine whether a swirl is a gradual response to the photospheric motion or an actual propagating Alfvénic wave. [ABSTRACT FROM AUTHOR]

We studied the physical parameters of the penumbra in a large and fully developed sunspot, one of the largest over the last two solar cycles, by using full-Stokes measurements taken at the photospheric Fe i 617.3 nm and chromospheric Ca ii 854.2 nm lines with the Interferometric Bidimensional Spectrometer. Inverting measurements with the Non-LTE inversion COde (NICOLE) code, we obtained the three-dimensional structure of the magnetic field in the penumbra from the bottom of the photosphere up to the middle chromosphere. We analyzed the azimuthal and vertical gradient of the magnetic field strength and inclination. Our results provide new insights on the properties of the penumbral magnetic fields in the chromosphere at atmospheric heights unexplored in previous studies. We found signatures of the small-scale spine and intraspine structure of both the magnetic field strength and inclination at all investigated atmospheric heights. In particular, we report typical peak-to-peak variations of the field strength and inclination of ≈300 G and ≈20°, respectively, in the photosphere, and of ≈200 G and ≈10° in the chromosphere. In addition, we estimated the vertical gradient of the magnetic field strength in the studied penumbra: we find a value of ≈0.3 G km−1 between the photosphere and the middle chromosphere. Interestingly, the photospheric magnetic field gradient changes sign from negative in the inner to positive in the outer penumbra. [ABSTRACT FROM AUTHOR]

We present results derived from the analysis of spectropolarimetric measurements of active region AR12546, which represents one of the largest sunspots to have emerged onto the solar surface over the last 20 years. The region was observed with full-Stokes scans of the Fe i 617.3 nm and Ca ii 854.2 nm lines with the Interferometric BIdimensional Spectrometer instrument at the Dunn Solar Telescope over an uncommon, extremely long time interval exceeding three hours. Clear circular polarization (CP) oscillations localized at the umbra–penumbra boundary of the observed region were detected. Furthermore, the multi-height data allowed us to detect the downward propagation of both CP and intensity disturbances at 2.5–3 mHz, which was identified by a phase delay between these two quantities. These results are interpreted as a propagating magnetohydrodynamic surface mode in the observed sunspot. [ABSTRACT FROM AUTHOR]

In this work we explore the possibility of using recurrence quantification analysis (RQA) in astronomical high-contrast imaging to statistically discriminate the signal of faint objects from speckle noise. To this end, we tested RQA on a sequence of high frame rate (1 kHz) images acquired with the SHARK-VIS forerunner at the Large Binocular Telescope. Our tests show promising results in terms of detection contrasts at angular separations as small as 50 mas, especially when RQA is applied to a very short sequence of data (2 s). These results are discussed in light of possible science applications and with respect to other techniques such as, for example, angular differential imaging and speckle-free imaging. [ABSTRACT FROM AUTHOR]

We present a new processing technique that significantly improves the angular differential imaging method (ADI). Its context of application is that of high-contrast imaging of faint objects nearby bright stars in observations obtained with extreme adaptive optics (EXAO) systems. This technique, named “SFADI” for “Speckle-Free ADI,” improves the achievable contrast by means of speckles identification and suppression. This is possible in very high cadence data, which freeze the atmospheric evolution. Here we present simulations in which synthetic planets are injected into a real millisecond frame rate sequence, acquired at the LBT telescope at a visible wavelength, and show that this technique can deliver a low and uniform background, allowing for unambiguous detection of 10−5 contrast planets, from 100 to 300 mas separations, under poor and highly variable seeing conditions (0.8 to 1.5 arcsec FWHM) and in only 20 minutes of acquisition. A comparison with a standard ADI approach shows that the contrast limit is improved by a factor of 5. We extensively discuss the SFADI dependence on the various parameters like the speckle identification threshold, frame integration time, and number of frames, as well as its ability to provide high-contrast imaging for extended sources and also to work with fast acquisitions. [ABSTRACT FROM AUTHOR]

In recent years, new high spatial resolution observations of the Sun's atmosphere have revealed the presence of a plethora of small-scale magnetic elements down to the resolution limit of the current cohort of solar telescopes (∼100–120 km on the solar photosphere). These small magnetic field concentrations, due to the granular buffeting, can support and guide several magnetohydrodynamic wave modes that would eventually contribute to the energy budget of the upper layers of the atmosphere. In this work, exploiting the high spatial and temporal resolution chromospheric data acquired with the Swedish 1 m Solar Telescope, and applying the empirical mode decomposition technique to the tracking of the solar magnetic features, we analyze the perturbations of the horizontal velocity vector of a set of chromospheric magnetic elements. We find observational evidence that suggests a phase relation between the two components of the velocity vector itself, resulting in its helical motion. [ABSTRACT FROM AUTHOR]

Small scale magnetic fields (magnetic elements) are ubiquitous in the solar photosphere. Their interaction can provide energy to the upper atmospheric layers, and contribute to heat the solar corona. In this work, the dynamic properties of magnetic elements in the quiet Sun are investigated. The high number of magnetic elements detected in a supergranular cell allowed us to compute their displacement spectrum 〈 (Δr)2〉 ∝τγ (with γ > 0, and τ the time since the first detection), separating the contribution of the network (NW) and the internetwork (IN) regions. In particular, we found γ = 1.27 ± 0.05 and γ = 1.08 ± 0.11 in NW (at smaller and larger scales, respectively), and γ = 1.44 ± 0.08 in IN. These results are discussed in light of the literature on the topic, as well as the implications for the build-up of the magnetic network. [ABSTRACT FROM AUTHOR]