Maria S. Madjarska

Context. Investigating the characteristics and formation mechanisms of plasma upflows at the edges of active regions (ARs) is essential for understanding the coupling between different layers of the solar atmosphere and the origin of the slow solar wind. Aims. The present study aims to statistically characterize AR upflows and investigate their properties and interrelation with the underlying photospheric magnetic field and chromospheric emission. Methods. We performed a statistical analysis of 30 ARs observed with the Extreme ultraviolet Imaging Spectrometer (EIS) on board the Hinode satellite using the Fe XII 195.12 Å line. We also analyzed the corresponding chromospheric 1600 Å intensity from the Atmospheric Imaging Assembly (AIA), the photospheric magnetic field measured by the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO), and the associated coronal magnetic field derived from the Potential-field Source-surface (PFSS) model. Results. Regions with blueshifted Fe XII 195.12 Å emission are present in all selected ARs. The blueshift speeds are strongly correlated with the corresponding nonthermal velocities. Compared with the AR same-polarity magnetic field concentration areas, blueshifted regions exhibit significantly weaker coronal intensity, comparable chromospheric intensity, and a weaker photospheric magnetic field. In the upflow regions, the Fe XII line intensity, blueshift speed, and nonthermal velocity are all positively correlated with the corresponding chromospheric intensity and photospheric magnetic field strength. For the ARs with unbalanced magnetic flux, regions with PFSS open magnetic field lines account for 78.6% and 35.7% of the majority- and minority-polarity areas, respectively. The corresponding fraction is 37.5% for ARs with relatively balanced magnetic flux. Blueshift regions with speeds exceeding 7 km s ⁻¹ occur at nearly identical rates in areas with (71.4%) and without (71.9%) PFSS open magnetic field lines. However, their area coverage is approximately 24% larger in regions with open magnetic field lines. Conclusions. The occurrence of AR upflow shows no clear association with PFSS open magnetic field lines, although blueshifted regions associated with open fields are approximately one-quarter larger. This suggests that a substantial fraction of AR boundary upflows may be associated with large-scale closed magnetic structures. The coronal upflow properties are positively correlated with the photospheric magnetic field strength and chromospheric intensity. This result suggests that stronger magnetic fields and enhanced chromospheric activity at the loop footpoints may drive greater upward transport of mass and energy. These findings support a cross-layer coupling scenario in which AR upflows are jointly regulated by the footpoint magnetic field, lower-atmosphere activity, and coronal open magnetic field topology.

We report an exceptionally strong increase in the photospheric horizontal magnetic field ( B _h ) during an M5.18-class solar flare observed with the 1.6 m Goode Solar Telescope at Big Bear Solar Observatory. The flare occurred in association with a filament eruption. The B _h increased by approximately 2000 G along a collisional polarity inversion line (cPIL), reaching a maximum value of about 4500 G during the flare. Subsequently, B _h decreased and stabilized at a permanently higher value than in the preflare phase. To our knowledge, this is the largest increase in B _h yet reported along a flaring cPIL. This nonmonotonic evolution differs from the step-like changes commonly reported in previous studies and suggests that the observed B _h increase may involve additional processes beyond coronal magnetic field restructuring alone. Our high-spatiotemporal-resolution spectropolarimetric observations reveal that the rapid and strong increase in B _h is closely associated with abrupt changes in the photospheric magnetic structures along the cPIL, together with the appearance of newly organized magnetic structures near the photosphere. These findings suggest that rapid reorganization of the photospheric magnetic structures during the flare contributes to the increase in B _h , providing new insight into the physical mechanisms underlying flare-related magnetic field evolution.

The origin of magnetic switchbacks—large-amplitude, spherically polarized magnetic-field fluctuations with local polarity inversions shown to be nearly ubiquitous in the inner heliosphere by Parker Solar Probe—is presently one of the most outstanding open questions in solar and heliospheric science. The occurrence of these structures in the young solar wind is a topic of active research, focusing not only on their characteristics and evolution but also on unraveling the puzzle of their origin. We first discuss the potential influence on switchback (SB) formation of large-scale coronal dynamics and restructuring processes that shape and regulate the extended solar corona. Following that, we review the dynamics, physical properties, occurrence rate, and energetics of numerous possible precursor small-scale dynamic events that occur throughout the solar atmosphere, emphasizing their possible roles in creating SBs. Finally, we discuss some recent studies attempting to connect in situ observations of SBs and SB patches with remote-sensing observations, and the related challenges in identifying solar wind source regions precisely and linking in situ observations to transient solar phenomena. We also clarify the terminology used by the solar community to describe small-scale solar phenomena.

Magnetic switchbacks are large-amplitude fluctuations in the interplanetary magnetic field, and appear frequently in the near-Sun solar wind explored recently by Parker Solar Probe: these new observations have prompted many new studies into their properties and origins. Here, we first review what is known about how switchbacks evolve as they travel away from the Sun: both in terms of their expansion-driven growth and their decay due to various processes like turbulence, reconnection, dispersion, parametric instability, and interaction with interplanetary shocks. We then review the current state of knowledge on how switchbacks impact the physics of the solar wind as a whole: in terms of the turbulent cascade, acceleration and heating of the wind, modification of the open solar flux and scattering of energetic particles. Finally, we suggest future studies to further our understanding of switchback evolution and impacts on the heliosphere.

Context. Transition-region loops are a type of critical magnetic structure in the solar atmosphere, yet their physical properties and evolutionary characteristics remain statistically poorly constrained. Aims. We aim to statistically characterize the physical properties of propagating brightening events in transition-region loops and to explore the underlying heating mechanism responsible for these brightenings. Methods. Using coordinated observations from the Extreme Ultraviolet Imager on board the Solar Orbiter and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, we analyzed 42 propagating brightening events in loops that are unambiguously detected in both sets of instrument data. Each of these events evolves simultaneously in the AIA 94, 131, 171, 193, 211, 304, and 335 Å passband images, suggesting that they are in the transition-region or low-coronal temperature range. Results. Our analyses show that these brightenings are impulsive, with an average brightening time of 118.4 ± 12.0 s and a mean intensity decreasing time of 159.4 ± 16.6 s. The propagating brightenings are predominantly subsonic, with velocities in the range of 0−90 km s ⁻¹ and an average of 51.3 ± 5.6 km s ⁻¹ . The lengths of brightenings range from 3 to 11 Mm, with an average and standard deviation of 6.3 ± 0.4 Mm, which are closely related to the propagation velocity and the lifetime. The initial brightening sites are predominantly located near the footpoints of these loops, and the number of brightening events decreases systematically with increasing loop height. Conclusions. Our results are consistent with an energizing mechanism regulated by enthalpy flows and radiative cooling. Dynamic magnetic evolution, including migration and cancellation, are taking place at the footpoints of these loops, and thus we suggest that magnetic cancellation, driven by reconnection and/or braiding that generate these brightenings, is a possible mechanism of plasma heating in a transition-region loop. Based on the measurements of these brightenings, we also propose a diagnostic method for the temperature or density of transition-region loops.

Magnetic switchbacks are large amplitude deflections of the magnetic field within the solar wind. They are Alfvénic in character and so are associated with a spike in velocity and a generally small variation in local plasma density. Early orbits of Parker Solar Probe revealed that the solar wind near the Sun is dominated by these structures, and therefore, they may be playing an important role in the energy budget and acceleration of the young solar wind. In this review, we present an overview of different mechanisms that have been proposed for how switchbacks could be formed. We group the mechanisms by whether they predominantly act in the low solar atmosphere or within the solar wind (in situ). We focus on mechanisms that can create reversals of the ambient magnetic field direction and, thus, account for the most extreme perturbations. The general consensus is that mechanisms in the lower solar atmosphere do not form such reversals on their own but provide the seed perturbations, flows, or particle beams necessary for in situ mechanisms to create switchbacks within the solar wind. Switchback observations thus likely contain an imprint of the coronal source of the seed perturbation or flow, which is evolved further locally by one of several plausible in situ mechanisms. We discuss the strengths and weaknesses of each mechanism and outline future observational and theoretical tests that could help differentiate between them.

Context. Previous studies have shown that a streamer blob might originate in the lower corona and thus be affected by activity in that region. While the base of one streamer might differ from that of another, it can be cataloged into two distinct types: active region streamers (ARSs) that have active regions at their base, and quiet equatorial streamers (QESs) that do not have an active region underneath. The difference between the blob properties in ARSs and those in QESs remains unknown. Aims. We compare the properties of propagating blobs in ARSs and QESs. Methods. By analyzing the whole-year observations from SOHO/LASCO/C2 in 2018, we carried out a statistical analysis of the properties of propagating blobs in ARSs and QESs. Results. We found that the properties of streamer blobs are very different from one blob to another. The occurrence rate of blobs in ARSs is about twice as high as that in QESs. On average, the ARS blobs have significantly higher initial velocities and slightly higher accelerations, but slightly lower heights of first appearance than the QES blobs. There is a weak positive correlation between the initial velocities and heights of first appearance in the two groups of streamer blobs. The correlation between the accelerations and heights of first appearance in ARS blobs is negative, while that in QES blobs is positive. Conclusions. Our results provide statistical evidence that a higher degree of activity at the coronal base of a streamer can cause more dynamic blobs higher up, and that it affects the structures of the solar wind originating in the region.

Context. The physical mechanisms of helium abundance ( A _He ) depletion in the corona and solar wind are closely linked to coronal heating, solar wind origin, and acceleration processes. The relationships between the A _He in the solar wind and the properties and activity of the source regions are crucial for understanding the depletion of A _He . Aims. We aim to investigate the impact of active region (AR) activity and properties on the A _He in the solar wind. Methods. First, we established the link between carefully selected ARs and the solar wind. Then, the AR chromospheric activity was quantitatively investigated using observations from the Atmospheric Imaging Assembly and Helioseismic Magnetic Imager on board the Solar Dynamics Observatory. The AR temperatures were derived with the differential emission measure method. We also statistically analyzed the A _He in the solar wind with higher and lower charge states during solar cycles 23 and 24. The parameters of solar wind were measured by the instruments on board ACE and Wind. Results. We find that an AR with greater chromospheric activity has higher A _He in its associated solar wind. The statistical analysis shows that the median A _He in solar wind with higher charge states is higher than A _He in solar wind with lower charge states. Conclusions. We conclude that chromospheric activity, primarily chromospheric evaporation processes, is possibly the main heating and transportation mechanism leading to a higher A _He in the corona and solar wind. This could also reasonably explain the variation in A _He in AR solar wind during different solar activity phases and the higher A _He in AR solar wind compared to quiet Sun solar wind.

On-disk H α light-absorbing plasma structures such as mottles, fibrils, filaments, and H α jets are observable magnetohydrodynamic features in the upper solar chromosphere. We attempt to determine their physical parameters by regarding them as optical clouds scattering the H α -line light incident from below. For this purpose, we developed a new inversion, which we call the three-layer background plus three-component cloud model inversion. This new spectral inversion was found to be applicable to every H α line profile taken from a quiet-Sun region. We used the model parameters inferred from the fitting to determine the temperature and to construct the velocity distribution function at every point in the observed region. This function was used in turn to calculate the column mass, mass flux, kinetic energy, and kinetic energy flux. Our approach yielded three types of Doppler velocities: the mass flux-associated velocity, the kinetic energy-associated velocity, and the kinetic energy flux-associated velocity. We found that the physical parameters of H α -absorbing structures in a quiet-Sun region resolve the long-standing discrepancy between the Doppler velocities of mottles observed on the disk and the rising speeds of spicules observed off the limb. We also found that the kinetic energy budget of the upper chromosphere is large enough for the radiative loss in the upper chromosphere and corona. These results support the hypothesis that magnetohydrodynamic waves heat the upper atmosphere of the quiet Sun.

Magnetic switchbacks are fluctuations in the solar wind in which the interplanetary magnetic field sharply deflects away from its background direction so as to create folds in magnetic field lines while remaining of roughly constant magnitude. The magnetic field and velocity fluctuations are extremely well correlated in a way corresponding to Alfvénic fluctuations propagating away from the Sun. For a background field which is nearly radial this causes an outwardly propagating jet to form. Switchbacks and their characteristic velocity jets have recently been observed to be nearly ubiquitous by Parker Solar Probe with in situ measurements in the inner heliosphere within 0.3 AU. Their prevalence, substantial energy content, and potentially fundamental role in the dynamics of the outer corona and solar wind motivate the significant research efforts into their understanding. Here we review the in situ measurements of these structures (primarily by Parker Solar Probe). We discuss how they are identified and measured, and present an overview of the primary observational properties of these structures, both in terms of individual switchbacks and their collective arrangement into “patches”. We identify both properties for which there is a strong consensus and those that have limited or qualified support and require further investigation. We identify and collate several open questions and recommendations for future studies.