Bright Points Research Articles

Small-scale dynamo in cool stars

Context. Some of the quiet solar magnetic flux could be attributed to a small-scale dynamo (SSD) operating in the convection zone. An SSD operating in cool main-sequence stars is expected to affect the atmospheric structure, in particular, the convection, and should have observational signatures. Aims. We investigate the distribution of SSD magnetic fields and their effect on bolometric intensity characteristics, vertical velocity, and spatial distribution of the kinetic energy (KE) and magnetic energy (ME) in the lower photosphere of different spectral types. Methods. We analyzed the SSD and purely hydrodynamic simulations of the near surface layers of F3V, G2V, K0V, and M0V stars. We compared the time-averaged distributions and power spectra in SSD setups relative to the hydrodynamic setup. The properties of the individual magnetic fields are also considered. Results. The probability density functions with a field strength at the τ = 1 surface are quite similar for all cases. The M0V star displays the strongest fields, but relative to the gas pressure, the fields on the F3V star reach the highest values. In all stars, the horizontal field is stronger than the vertical field in the middle photosphere, and this excess becomes increasingly prominent toward later spectral types. These fields result in a decrease in the upflow velocities and a slight decrease in granule size, and also lead to formation of bright points in intergranular lanes. The spatial distribution of the KE and ME is also similar for all cases, implying that important scales are proportional to the pressure scale height. Conclusions. The SSD fields have rather similar effects on the photospheres of cool main-sequence stars: a significant reduction in convective velocities, as well as a slight reduction in granule size and a concentration of the field to kilogauss levels in intergranular lanes that is associated with the formation of bright points. The distribution of the field strengths and energies is also rather similar.

Применение зондирующих ФКМ-сигналов с нулевой зоной автокорреляции для улучшения качества измерений в РСА

For SARs, a polyphase (p-phase, where p is a prime number) probing signal with a zero autocorrelation zone has been synthesized, which is a train of p phase-code shift keyed (PCSK) pulses coded by complementary sequences of a p-ary D-code with additional phase-code shift-keying of the sub-pulses (discretes) of pulses by an M-sequences. To assess the quality of radar images of point targets and extended surfaces, the levels of the maximum side lobe and one-way integrated correlation noise of the autocorrelation function (ACF) are used, respectively. For this purpose, the work carried out a comparative analysis of the total ACFs of the synthesized ensemble of signals with ensembles of orthogonal chirp and PCSK-signals used in adjacent SAR sounding cycles. The work also considers the problem of superimposition of SAR echo signals from different ranges at a relatively high repetition rate of probing pulses. To assess the level of suppression of recurrent interference from point targets and from extended surfaces, the levels of the maximum side lobe and one-sided integral correlation noise of the cross-correlation function (CCF) are used, respectively. For this purpose, the work carried out a comparative analysis of the total CCFs of the synthesized ensemble of signals with ensembles of orthogonal chirp and PCSK- signals used in the SAR aperture synthesis modes. The use of orthogonal chirp and PCSK-signals makes it possible to successfully suppress false signals from bright point targets from adjacent repetition periods. However, the high level of integral correlation noise of the CCF of orthogonal signals distorts radar images of weakly reflecting surfaces located next to bright extended objects. The indicators of the total correlation characteristics of the synthesized ensemble of signals exceed the corresponding indicators of the total correlation characteristics of the ensemble of orthogonal PCSK-and chirp signals, both without mismatch and with Doppler frequency mismatch. This makes it possible to successfully use an PCSK-signal with a zero autocorrelation zone to improve the quality of radar images and suppress recurrent range interference in SAR.

Client and Therapists’ Subjective Understanding of an Ideal Therapy Room: A Divergent Reflection of Experience

An abundance of studies showed that the room/space where therapy takes place could significantly impact the engagement, process, and how people experience therapy. The need to balance the comfort of the room with its fundamental functionality to clients is essential. Nevertheless, studies that report on the perception of therapists and clients about an ideal therapy room are scarce. This study, therefore, aimed to explore the subjective understanding of what makes an ideal therapy room from the perspective of clients and therapists. The study utilised a qualitative descriptive research design and adopted a grounded theory method. Eight participants (three therapists and five clients) volunteered to participate in the study. The participants were purposively recruited for the study and participated in individual semi-structured interviews. Data obtained were transcribed verbatim and subjected to thematic analysis. Results showed divergent views among the participants about what constitutes an ideal therapy room. Confidentiality, spatial environment, contextual awareness, and privacy were the key emergent themes. Several subthemes pointed to comfortability, brightness, colour, nice viewing, and focus points as recurrent issues determining how ideal the participants perceive a therapy room. Conclusion The results align with Rapoport’s (1992) meaning of the built environment, which emphasises the variability of peoples’ reactions to the environment in terms of its meanings. Implication The study implicates the need for therapists working with clients in therapy rooms to consider what the room means to their clients and tailor the environment to suit their clients’ preferences as much as possible or make this an object of exploration at the start of the session. The built environment designers will also benefit from considering these points perceived as significant.

KONTRIBUSI FAKTOR FISIKA KELAUTAN TERHADAP PEMBUDIDAYAAN RUMPUT LAUT (EUCHEUMA COTTONII) DI DESA RIA BAO KECAMATAN NAGAWUTUNG KABUPATEN LEMBATA

Research Objectives To determine the contribution of marine physics factors to the cultivation of seaweed (Eucheuma cottonii) in Ria Bao Village, Nagawutung District, Lembata Regency.This type of research uses quantitative research. The population in this study is the coastal area of ​​Ria Bao Village, Nagawutung District, Lembata Regency. The sample in the study was taken from the entire population, namely there are three points for determining the location of seaweed cultivation in the coastal area of Ria Bao Village, Nagawutung District, Lembata Regency. The three points were chosen intentionally (purposive sampling). It is planned to measure marine physical factors with a distance of 0.5 to 1 km from the shoreline to the sea, or a depth limit that is still possible for the development of seaweed cultivation.Data sources consist of primary data and secondary data. Data collection techniques are observation, and documentation. The analysis technique is using matrix of land suitability for seaweed cultivation. Research Results (1) The Contribution of Marine Physics Factors to Seaweed Cultivation is the Current Speed Factor (point 1=0.18m/s, point 2=0.30m/s, point 3=0.21m/s), Sea Depth (point 1=3.81 m, point 2=1.93 m, point 3=3.57 m), Brightness (point 1=2.80 m, point 2=1.20 m, point 3=1.60 m) , Temperature (point 1=290C, point 2=300C, point 3=300C), and tides (0.30 m) .

Deciphering Solar Coronal Heating: Energizing Small-scale Loops through Surface Convection

The solar atmosphere is filled with clusters of hot small-scale loops commonly known as coronal bright points (CBPs). These ubiquitous structures stand out in the Sun by their strong X-ray and/or extreme-ultraviolet (EUV) emission for hours to days, which makes them a crucial piece when solving the solar coronal heating puzzle. In addition, they can be the source of coronal jets and small-scale filament eruptions. Here we present a novel 3D numerical model using the Bifrost code that explains the sustained CBP heating for several hours. We find that stochastic photospheric convective motions alone significantly stress the CBP magnetic field topology, leading to important Joule and viscous heating concentrated around the CBP’s inner spine at a few megameters above the solar surface. We also detect continuous upflows with faint EUV signals resembling observational dark coronal jets and small-scale eruptions when Hα fibrils interact with the reconnection site. We validate our model by comparing simultaneous CBP observations from the Solar Dynamics Observatory (SDO) and the Swedish 1‐m Solar Telescope (SST) with observable diagnostics calculated from the numerical results for EUV wavelengths as well as for the Hα line using the Multi3D synthesis code. Additionally, we provide synthetic observables to be compared with Hinode, Solar Orbiter, and the Interface Region Imaging Spectrograph (IRIS). Our results constitute a step forward in the understanding of the many different facets of the solar coronal heating problem.

Coherent deflection pattern and associated temperature enhancements in the near-Sun solar wind

ABSTRACT Measurements of transverse magnetic field and velocity components from Parker Solar Probe have revealed a coherent quasi-periodic pattern in the near-Sun solar wind. As well as being Alfvénic and arc-polarized, these deflections were characterized by a consistent orientation and an increased proton core temperature, which was greater parallel to the magnetic field. We show that switchbacks represent the largest deflections within this underlying structure, which is itself consistent with the expected outflow from interchange reconnection simulations. Additionally, the spatial scale of the deflections was estimated to be around 1 Mm on the Sun, comparable to the jetting activity observed at coronal bright points within the base of coronal plumes. Therefore, our results could represent the in situ signature of interchange reconnection from coronal bright points within plumes, complementing recent numerical and observational studies. We also found a consistent relationship between the proton core temperature and magnetic field angle across the Parker Solar Probe encounters and discussed how such a persistent signature could be more indicative of an in situ mechanism creating a local increase in temperature. In future, observations of minor ions, radio bursts, and remote sensing images could help further establish the connection between reconnection events on the Sun and signatures in the solar wind.

Small-Scale Upflows in a Coronal Hole – Tracked from the Photosphere to the Corona

Coronal transients are known as sources of coronal upflows. With the commissioning of Solar Orbiter, it became apparent that coronal small-scale features are even more frequent than previously estimated. It was found that even small coronal features seen by Solar Orbiter can produce visible upflows. Therefore, it is important to study the plasma flows on small scales better and understand their atmospheric driving mechanisms.In this article, we present the results from a two-week coordinated multi-spacecraft observation campaign with Hinode, IRIS, and the GREGOR telescope. We identify a small region of coronal upflows with Doppler velocities of up to 16.5 km s−1. The upflows are located north of a coronal bright point in a coronal hole. We study the corona, the transition region, the chromosphere and the photospheric magnetic field to find evidence of underlying mechanisms for the coronal upflow. We find a complex photospheric magnetic field with several small mixed polarities that are the footpoints of different loops. Flux emergence and cancellation are observed at the constantly changing footpoints of the coronal loops. Reconnection of loops can be identified as the driver of the coronal upflow. Furthermore, the impact of the coronal activity triggers plasma flows in the underlying layers. This work highlights that frequent small coronal features can cause considerable atmospheric response and ubiquitously produce plasma upflows that potentially feed into the solar wind.

Automated analysis of oscillations in coronal bright points

Context. Coronal bright points (BPs) are numerous, bright, small-scale dynamical features found in the solar corona. Bright points have been observed to exhibit intensity oscillations across a wide range of periodicities and are likely an important signature of plasma heating and/or transport mechanisms. Aims. We present a novel and efficient wavelet-based method that automatically detects and tracks the intensity evolution of BPs using images from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) in the 193 Å bandpass. Through the study of a large, statistically significant set of BPs, we attempt to place constraints on the underlying physical mechanisms. Methods. We used a continuous wavelet transform (CWT) in 2D to detect the BPs within images. One-dimensional CWTs were used to analyse the individual BP time series to detect significant periodicities. Results. We find significant periodicity at 4, 8–10, 17, 28, and 65 min. Bright point lifetimes are shown to follow a power law with exponent −1.13 ± 0.07. The relationship between the BP lifetime and maximum diameter similarly follows a power law with exponent 0.129 ± 0.011. Conclusions. Our wavelet-based method successfully detects and extracts BPs and analyses their intensity oscillations. Future work will expand upon these methods, using larger datasets and simultaneous multi-instrument observations.

Orientation and distribution relative to the polarity dividing line of two types of coronal bright points

Based on synoptic maps, the orientation and localization (distribution) of coronal bright points (CBP) relative to the polarity line (PL) on the Sun is studied. Preliminary results show that the slope of the CBP angles of the quiet Sun is oriented, in most cases, parallel to the solar equator, while for the CBP of the active Sun it is more randomly distributed. The question of the localization of both types of CBP with respect to active formations and PL is not so clear and requires a more detailed study.

Hybrid Detection Algorithm and Study on the Quantity and Brightness Evolution Characteristics of Photospheric Bright Point Groups

Photospheric bright points (BPs), the smallest magnetic elements in the photosphere, are constantly moving and changing. Studying the characteristics of these small-scale strong magnetic fields with kilogauss magnitudes could be of significant importance for investigating the coronal heating problem. Compared to the study of a few specific BPs, investigating the collective features of BP groups can provide us with a better understanding of the overall characteristics of BPs. However, there is still a lack of research on the evolution of BP groups, and the detection algorithm of BPs still has a lot of space for improvement. We propose a hybrid BP detection model (HBD-Model) that combines traditional algorithms and deep learning to improve detection accuracy. Using the HBD-Model, we focus on studying the evolution characteristics of the quantity and brightness of BP groups at different brightness levels and how these characteristics differ between quiet and active regions. Results show that the activity of BP groups is not random or disorderly. In different brightness levels and regions, their quantity and brightness evolution exhibit periodic or complex changes.

Beyond small-scale transients: A closer look at the diffuse quiet solar corona

Aims. Within the quiet Sun corona imaged at 1 MK, much of the field of view consists of diffuse emission that appears to lack the spatial structuring that is so evident in coronal loops or bright points. Our aim is to determine if these diffuse regions are categorically different in terms of their intensity fluctuations and spatial configuration from the better-studied dynamic coronal features. Methods. We analyzed a time series of observations from Solar Orbiter’s High Resolution Imager in the extreme ultraviolet to quantify the characterization of the diffuse corona at high spatial and temporal resolutions. We then compared this to the dynamic features within the field of view, mainly a coronal bright point. Results. We find that the diffuse corona lacks visible structuring, such as small embedded loops, and that this is persistent over the 25 min duration of the observation. The intensity fluctuations of the diffuse corona, which are within ±5%, are significantly smaller in comparison to the coronal bright point; however, the total intensity observed in the diffuse corona is on the same order as the bright point. Conclusions. It seems inconsistent with our data that the diffuse corona is a composition of small loops or jets or that it is driven by discrete small heating events that follow a power-law-like distribution. We speculate that small-scale processes such as magnetohydrodynamic turbulence might be energizing the diffuse regions, but at this point we cannot offer a conclusive explanation for the nature of this feature.

Coronal bright point statistics

Context. The corona of the Sun is the part of the solar atmosphere with temperatures of over one million Kelvin, which needs to be heated internally in order to exist. This heating mechanism remains a mystery; we see large magnetically active regions in the photosphere lead to strong extreme UV (EUV) emission in the corona. On much smaller scales (on the order of tens of Mm), there are bipolar and multipolar regions that can be associated with evenly sized coronal bright points (CBPs). Aims. Our aim was to study the properties of CBPs in a statistical sense and to use continuous data from the SDO spacecraft, which makes it possible to track CBPs over their whole lifetime. Furthermore, we tested various rotation-speed profiles for CBPs in order to find out if the lower corona is co-rotating with the photosphere. Then we compiled a database with about 346 CBPs together with information of their sizes, shapes, appearance and disappearance, and their visibility in the EUV channels of the AIA instrument. We want to verify our methods with similar previous studies. Methods. We used the high-cadence data of the largest continuous SDO observation interval in 2015 to employ an automated tracking algorithm for CBPs. Some of the information (e.g., the total lifetime, the characteristic shape, and the magnetic polarities below the CBPs) still requires human interaction. Results. In this work we present statistics on fundamental properties of CBPs along with some comparison tables that relate, for example, the CBP lifetime with their shape. CBPs that are visible in all AIA channels simultaneously seem to be brighter in total and also have a stronger heating, and hence a higher total radiation flux. We compared the EUV emission visibility in different AIA channels with the CBP’s shape and lifetime. From the tracking algorithm we confirm a strict co-rotation of the CBPs with the photospheric differential rotation. Conclusions. The tracked CBPs have a typical lifetime of about 1–6 h, while the hottest and brightest ones seem to exist for significantly longer time, up to 24 h. Furthermore, the merging of two CBPs seems not to have an influence on the overall size of the persisting CBP. Finally, fainter and cooler CBPs tend to have only weaker magnetic polarities, which clearly supports a coronal bright point heating mechanism based on magnetic energy dissipation.

Photospheric magnetic flux and coronal emission properties of small-scale bright and faint loops in the quiet Sun

Context. The study explores the photospheric magnetic properties of bright and faint small-scale loop systems in the solar atmosphere of the quiet Sun, also known as X-ray or coronal bright points. Aims. To understand how plasma confined in small-scale loops is heated to million degrees, the loop-associated photospheric and coronal magnetic flux properties should be known because the magnetic field is generally assumed to be the main energy source or waveguide. This and follow-up studies aim to provide a qualitative and quantitative investigation of these magnetic properties and their impact on the heating of plasma to million degrees. Methods. We used quasi-temporal imaging observations taken in the 193 Å channel of the Atmospheric Imaging Assembly (AIA) and line-of-sight magnetograms from the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory. The observations cover 48 h of data at a 6 min cadence with a field of view of 400″ × 400″, from which 90 loop systems (of which 83 are CBPs) were extracted and analysed in full detail. Results. We obtain the evolution properties of both faint and bright small-scale loop systems (SSLSs) related to either magnetic flux emergence or magnetic flux coalescence and a chance encounter of magnetic fluxes. We estimate the lifetimes of the two loop systems and the impact of the magnetic flux evolution on their life span. The photospheric magnetic flux associated with SSLSs confining plasma heated to coronal temperatures is found to cover at least two orders of magnitude from 3.0 × 1018 Mx to 1.8 × 1020 Mx. The analysis of the maximum intensity of SSLSs during their lifetime shows numerous spikes of intensity that are identified as small (a few AIA pixels) compact brightenings associated with cancelling magnetic fluxes. Most of them are identified as microflares. The intensity flux range of these spikes is reported. The coronal intensity flux evolution of SSLSs is strongly correlated with the total unsigned photospheric magnetic flux evolution when there is little or no contamination in the selected field of view of the SSLSs by unrelated magnetic fluxes or intensity features. We report on the footpoint separation and change during the lifetime of the faint and bright SSLSs. The magnetic flux emergence and decay rates of some of the SSLSs are also provided in this study. Conclusions. The power-law index α of the logarithm of the total unsigned magnetic flux and the total intensity for the full lifetime of SSLSs is 1.10 ± 0.02, compared with 1.14 ± 0.03 for a previous study of the whole disc in the same intensity range (Fe XII 193–195 Å). This indicates that the emission of the corona of the quiet Sun at ∼1.25 MK is mostly confined to small-scale loops (some brighter, others fainter). Therefore, it is imperative to understand the mechanism that heats the plasma in these loops.

The motions of photospheric bright points

Photospheric magnetic bright points (PBPs) are considered reliable tracers of footpoints of magnetic flux tubes. Their evolution could demonstrate the behaviors of magnetic flux tube footpoints. In this work we firstly analyzed a PBP case in detail and found the magnetic flux inside the PBP moved fast in a short time with horizontal velocity of 8 km/s which is even faster than the footpoint traced by the PBP observed by imaging data at 388 nm wavelength. In this short moment, 60% of the magnetic flux move fast ahead, a few stood still. Continually, we identified another 35 isolated BPs and analyzed the instantaneous velocities calculated by vertical flux and by intensity. We obtained a total of 313 instantaneous velocities, and found that about 7% of measurements derived by vertical flux had values at least 1 km/s larger than those derived by intensity, and another 7% derived by intensity had speeds at least 1 km/s faster than calculated by magnetic flux for the same flux tubes. Whether this difference can excite MHD waves is still unclear and need more analysis in future.

A deep learning approach for automated segmentation of magnetic bright points in the solar photosphere

Context. Magnetic bright points (MBPs) are small, bright, and conspicuous magnetic structures observed in the solar photosphere and are widely recognized as tracers of magnetic flux tubes. Previous studies have underscored the significance of MBPs in elucidating the mechanisms of coronal heating. The continuous advancement of solar telescopes and observation techniques has significantly enhanced the resolution of solar images, enabling a more detailed examination of MBP structures. In light of the growing availability of MBP observation images, the implementation of large-scale automated and precise MBP segmentation methods holds tremendous potential to facilitate significant progress in solar physics research. Aims. The objective of this study is to propose a deep learning network called MBP-TransCNN that enables the automatic and precise pixel-level segmentation of MBPs in large quantities, even with limited annotated data. This network is designed to effectively handle MBPs of various shapes and backgrounds, including those with complex features. Methods. First, we normalized our sample of MBP images. We then followed this with elastic deformation and rotation translation to enhance the images and expand the dataset. Next, a dual-branch encoder was used to extract the features of the MBPs, and a Transformer-based global attention mechanism was used to extract global contextual information, while a convolutional neural network (CNN) was used to extract detailed local information. Afterwards, an edge aware module was proposed to extract detailed edge features of MBPs, which were used to optimize the segmentation results. Focal loss was used during the training process to address the problem of the small number of MBP samples. Results. The average values of precision, recall, F1, pixel accuracy, and intersection over union of the MBP-TransCNN are 0.976, 0.827, 0.893, 0.999, and 0.808, respectively. Experimental results show that the proposed MBP-TransCNN deep learning network can quickly and accurately segment the fine structure of MBPs.

Similarity measurement tracking and properties evolution of photospheric bright point groups in the quiet Sun and active region

ABSTRACT Photospheric bright points (BPs) fast movement is more effective than the slow movement that occurs most of the time in transmitting energy to the corona. The splitting and merging BPs tend to produce relatively large velocities. Therefore, our aim is to detect and track BP groups. After that, the attribute distribution of BP groups and the attribute evolution under possible high-speed movement are studied and analysed. We use a new BPs detection model (HBD-model) that can effectively detect weak BPs and layered BPs and then use similarity measures to judge the splitting and merging of BPs for tracking. The average accuracy of the BPs detection algorithm is 0.74, and the average accuracy of tracking is more than 85 per cent. For the BPs in the quiet Sun (QS) and active region (AR), a total of 62 388 evolutionary BPs were identified and tracked. The average velocities are more than 2 km s−1 in the QS and ARs. For the QS and ARs, the evolution process of splitting or merging BPs is basically the same. The results show that for the merged BPs, the area and velocity of the BPs are tiny in the initial stage, reach a peak in the middle stage, and then become smaller and disappear. The area, intensity contrast, and velocity of the BPs with splitting are relatively tiny at the beginning, become larger at the middle stage, reach the peak after splitting, and then become smaller and disappear rapidly.

High-resolution Observations of Plume Footpoints in a Solar Coronal Hole

Plumes are bright structures in coronal holes extending from the solar surface into the corona and are considered as a possible source of the solar wind. Plumes are thought to be rooted in strong unipolar photospheric flux patches (network/plage region). The magnetic activities at the base of plumes may play a crucial role in producing outflows and propagating disturbances (PDs). However, the role of photospheric/chromospheric activities (e.g., jets/spicules) at the base of plumes and their connection to PDs is poorly understood. Using high-resolution observations of a plume taken on 2020 July 23 with the 1.6 m Goode Solar Telescope (GST), Interface Region Imaging Spectrograph (IRIS), and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory, we analyzed chromospheric/transition region activities at the base of the plume and their connection to outflows/PDs in the plume. The GST Visible Imaging Spectrometer images reveal repetitive spicules with blueshifted emission (pseudo-Doppler maps) at the plume’s footpoint. In addition, the photospheric magnetograms provide evidence of mixed polarities at the base of the plume. The IRIS Mg ii k Dopplergrams show strong blueshifted emission (∼50 km s−1) and a high brightness temperature (Mg ii k2 line) at the footpoint of the plume. The long-period PDs (P ≈ 20–25 minutes) along the plume (AIA 171 Å) match the periodicity of spicules in the chromospheric images, suggesting a close connection between the spicules and the PDs. We suggest that the interchange reconnection between the closed and open flux of the coronal bright point at the plume’s footpoint is the most likely candidate to produce upflows and associated PDs along the plume.

New Evidence on the Origin of Solar Wind Microstreams/Switchbacks

Microstreams are fluctuations in the solar wind speed and density associated with polarity-reversing folds in the magnetic field (also denoted switchbacks). Despite their long heritage, the origin of these microstreams/switchbacks remains poorly understood. For the first time, we investigated periodicities in microstreams during Parker Solar Probe (PSP) Encounter 10 to understand their origin. Our analysis was focused on the inbound corotation interval on 2021 November 19–21, while the spacecraft dove toward a small area within a coronal hole (CH). Solar Dynamics Observatory remote-sensing observations provide rich context for understanding the PSP in situ data. Extreme ultraviolet images from the Atmospheric Imaging Assembly reveal numerous recurrent jets occurring within the region that was magnetically connected to PSP during intervals that contained microstreams. The periods derived from the fluctuating radial velocities in the microstreams (approximately 3, 5, 10, and 20 minutes) are consistent with the periods measured in the emission intensity of the jetlets at the base of the CH plumes, as well as in larger coronal jets and in the plume fine structures. Helioseismic and Magnetic Imager magnetograms reveal the presence of myriad embedded bipoles, which are known sources of reconnection-driven jets on all scales. Simultaneous enhancements in the PSP proton flux and ionic (3He, 4He, Fe, O) composition during the microstreams further support the connection with jetlets and jets. In keeping with prior observational and numerical studies of impulsive coronal activity, we conclude that quasiperiodic jets generated by interchange/breakout reconnection at CH bright points and plume bases are the most likely sources of the microstreams/switchbacks observed in the solar wind.

Topologically protected optical polarization singularities in four-dimensional space.

Optical singularities play a major role in modern optics and are frequently deployed in structured light, super-resolution microscopy, and holography. While phase singularities are uniquely defined as locations of undefined phase, polarization singularities studied thus far are either partial, i.e., bright points of well-defined polarization, or are unstable for small field perturbations. We demonstrate a complete, topologically protected polarization singularity; it is located in the four-dimensional space spanned by the three spatial dimensions and the wavelength and is created in the focus of a cascaded metasurface-lens system. The field Jacobian plays a key role in the design of such higher-dimensional singularities, which can be extended to multidimensional wave phenomena, and pave the way for unconventional applications in topological photonics and precision sensing.

The Merging of a Coronal Dimming and the Southern Polar Coronal Hole

We report on the merging between the southern polar coronal hole and an adjacent coronal dimming induced by a coronal mass ejection on 2022 March 18, resulting in the merged region persisting for at least 72 hr. We use remote sensing data from multiple co-observing spacecraft to understand the physical processes during this merging event. The evolution of the merger is examined using Extreme-UltraViolet (EUV) images obtained from the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory and Extreme Ultraviolet Imager, which is on board the Solar Orbiter spacecraft. The plasma dynamics are quantified using spectroscopic data obtained from the EUV Imaging Spectrometer on board Hinode. The photospheric magnetograms from the Helioseismic and Magnetic Imager are used to derive the magnetic field properties. To our knowledge, this work is the first spectroscopical analysis of the merging of two open-field structures. We find that the coronal hole and the coronal dimming become indistinguishable after the merging. The upflow speeds inside the coronal dimming become more similar to that of a coronal hole, with a mixture of plasma upflows and downflows observable after the merging. The brightening of the bright points and the appearance of coronal jets inside the merged region further imply ongoing reconnection processes. We propose that component reconnection between the coronal hole and coronal dimming fields plays an important role during this merging event because the footpoint switching resulting from the reconnection allows the coronal dimming to intrude onto the boundary of the southern polar coronal hole.