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This study presents observations of a large pseudostreamer solar eruption and, in particular, the post-eruption relaxation phase, as captured by Metis onboard the Solar Orbiter on October 12, 2022, during its perihelion passage. Utilizing total brightness data, we observe the outward propagation of helical features up to 3 solar radii along a radial column that appears to correspond to the stalk of the pseudostreamer. The helical structures persisted for more than 3 hours following a jet-like coronal mass ejection associated with a polar crown prominence eruption. A notable trend is revealed: the inclination of these features decreases as their polar angle and height increase. Additionally, we measured their helix pitch. Despite a 2-minute time cadence limiting direct correspondence among filamentary structures in consecutive frames, we find that the Metis helical structure may be interpreted as a consequence of twist (nonlinear torsional Alfv\'{e}n waves) and plasma liberated by interchange reconnection. A comparison was performed of the helix parameters as outlined by fine-scale outflow features with those obtained from synthetic white-light images derived from the high-resolution magnetohydrodynamics simulation of interchange reconnection in a pseudostreamer topology by Wyper et al. (2022). A remarkable similarity between the simulation-derived images and the observations was found. We conjecture that these Metis observations may represent the upper end in spatial and energy scale of the interchange reconnection process that has been proposed recently as the origin of the Alfv\'{e}nic solar wind.

Metis, the coronagraph on board Solar Orbiter, provides for the first time coronagraphic imaging in the ultraviolet HI Ly-alpha line and, simultaneously, in polarized visible light, thus providing a host of information on the properties of CMEs and solar eruptions like their overall dynamics, time evolution, mass content, and outflow propagation velocity in the expanding corona. We analyzed in this work six CMEs observed by Metis between April and October 2021, which are characterized by a very strong HI Ly-alpha emission. We studied in particular the morphology, kinematics, and the temporal and radial evolution of the emission of such events, focusing on the brightest UV features. The kinematics of the eruptive events under consideration were studied by determining the height-time profiles of the brightest parts on the Metis plane of the sky. Furthermore, the 3D position in the heliosphere of the CMEs were determined by employing co-temporal images from two other coronagraphs: LASCO/C2 onboard SOHO, and COR2 onboard STEREO-A. Finally, the radiometrically calibrated Metis images of the bright UV features were analyzed to provide estimates of their volume and density. From the kinematics and radiometric analyses, we obtained indications of the temperatures of the bright UV cores of these events. The analysis of these strong UV-emitting features associated with coronal mass ejections demonstrates the capabilities of the current constellation of space coronagraphs, Metis, LASCO/C2, and COR2, in providing a complete characterization of the structure and dynamics of eruptive events in their propagation phase from their inception up to several solar radii. Furthermore, we show how the unique capabilities of the Metis instrument to observe these events in both HI Ly-alpha line and polarized VL radiation allow plasma diagnostics on the thermal state of these events., Comment: 26 pages, 26 figures, 2 appendices

Ultraviolet spectra of Comet 96/P Machholz were obtained during its 2002 perihelion with the UVCS instrument aboard the SOHO satellite. Emission from H I, C II, C III, and O I, is detected near the nucleus. The outgassing rate is in line with the value extrapolated from rates at larger distances from the Sun, and abundances of C and O are estimated. Reconstructed images show a nearly spherical cloud in H I Ly$\alpha$ emission and an ion tail seen in C III. Radiation pressure on the hydrogen atoms produces a modest distortion of the shape of the Ly$\alpha$ cloud as seen from SOHO, and it produces Doppler shifts up to 30 km s$^{-1}$ in the outer parts of the cloud. We estimate a ratio of C to H$_2$O similar to what is observed in other comets, so low carbon abundance does not account for the anomalously low C$_2$ and C$_3$ ratios to NH$_2$ observed at optical wavelengths.

This work deals with the analysis of longitudinal ordinal responses. The novelty of the proposed approach is in modeling simultaneously the temporal dynamics of a latent trait of interest, measured via the observed ordinal responses, and the answering behaviors influenced by response styles, through hidden Markov models (HMMs) with two latent components. This approach enables the modeling of (i) the substantive latent trait, controlling for response styles; (ii) the change over time of latent trait and answering behavior, allowing also dependence on individual characteristics. For the proposed HMMs, estimation procedures, methods for standard errors calculation, measures of goodness of fit and classification, and full-conditional residuals are discussed. The proposed model is fitted to ordinal longitudinal data from the Survey on Household Income and Wealth (Bank of Italy) to give insights on the evolution of the Italian households financial capability.

The determination of solar wind outflow velocity is fundamental in order to probe the mechanisms of wind acceleration in the corona. We aim to study, via the Doppler dimming technique, the effects that the chromospheric Ly{\alpha} line profile shape causes on the determination of the outflow speed of coronal HI atoms. The Doppler dimming technique takes into account the decrease of coronal Ly{\alpha} radiation in regions where HI atoms flow out in the solar wind. Starting from UV observations (UVCS/SOHO) of the coronal Ly{\alpha} line and simultaneous measurements of pB (LASCO/SOHO and Mk3/MLSO), we studied the effect of the pumping chromospheric Ly{\alpha} line profile through measurements from SOHO/SUMER, UVSP/SMM and LPSP/OSO-8, taken from representative on-disk regions and as a function of time during the solar activity cycle. In particular, we considered the effect of four chromospheric line parameters: line width, depth of the central reversal, asymmetry and distance of the peaks. We find that the range of variability of these parameters is of about 50% for the width, 69% for the depth of the central reversal, 35% for the asymmetry, and 50% for the distance of the peaks. Then, we find that the variability of the pumping Ly{\alpha} profile affects the estimates of the coronal HI velocity by about 9-12%. Therefore, this uncertainty is smaller than other physical quantities uncertainties, and a constant in time and unique shape of the Ly{\alpha} profile over the solar disk can be adopted in order to estimate the solar wind outflow velocity., Comment: 12 pages, 10 figures, 1 table, it will appear in "Astronomy & Astrophysics", accepted for "ESPM-16" and "SWICo 2021", the uploaded abstract is abridged

We report the first unambiguous observational evidence in the radio range of the reflection of a coronal shock wave at the boundary of a coronal hole. The event occurred above an active region located at the northwest limb of the Sun and was characterized by an eruptive prominence and an extreme-ultraviolet (EUV) wave steepening into a shock. The EUV observations acquired by the Atmospheric Imaging Assembly (AIA) instrument on board the Solar Dynamics Observatory(SDO) and the Extreme Ultraviolet Imager (EUVI) instrument on board the Solar TErrestrial RElations Observatory(STEREO-A) were used to track the development of the EUV front in the inner corona. Metric type II radio emission, a distinguishing feature of shock waves propagating in the inner corona, was simultaneously recorded by ground-based radio spectrometers. The radio dynamic spectra displayed an unusual reversal of the type II emission lanes, together with type III-like herringbone emission, indicating shock-accelerated electron beams. Combined analysis of imaging data from the two space-based EUV instruments and the Nancay Radioheliograph (NRH) evidences that the reverse-drifting typeiiemission was produced at the intersection of the shock front, reflected at a coronal hole boundary, with an intervening low-Alfv\'en-speed region characterized by an open field configuration. We also provide an outstanding data-driven reconstruction of the spatiotemporal evolution in the inner corona of the shock-accelerated electron beams produced by the reflected shock., Comment: Accepted by Astronomy & Astrophysics, 6 pages, 7 figures

The investigation of the wind in the solar corona initiated with the observations of the resonantly scattered UV emission of the coronal plasma obtained with UVCS-SOHO, designed to measure the wind outflow speed by applying the Doppler dimming diagnostics. Metis on Solar Orbiter complements the UVCS spectroscopic observations, performed during solar activity cycle 23, by simultaneously imaging the polarized visible light and the HI Ly-alpha corona in order to obtain high-spatial and temporal resolution maps of the outward velocity of the continuously expanding solar atmosphere. The Metis observations, on May 15, 2020, provide the first HI Ly-alpha images of the extended corona and the first instantaneous map of the speed of the coronal plasma outflows during the minimum of solar activity and allow us to identify the layer where the slow wind flow is observed. The polarized visible light (580-640 nm), and the UV HI Ly-alpha (121.6 nm) coronal emissions, obtained with the two Metis channels, are combined in order to measure the dimming of the UV emission relative to a static corona. This effect is caused by the outward motion of the coronal plasma along the direction of incidence of the chromospheric photons on the coronal neutral hydrogen. The plasma outflow velocity is then derived as a function of the measured Doppler dimming. The static corona UV emission is simulated on the basis of the plasma electron density inferred from the polarized visible light. This study leads to the identification, in the velocity maps of the solar corona, of the high-density layer about +/-10 deg wide, centered on the extension of a quiet equatorial streamer present at the East limb where the slowest wind flows at about (160 +/- 18) km/s from 4 Rs to 6 Rs. Beyond the boundaries of the high-density layer, the wind velocity rapidly increases, marking the transition between slow and fast wind in the corona.

SWELTO -- Space WEather Laboratory in Turin Observatory is a conceptual framework where new ideas for the analysis of space-based and ground-based data are developed and tested. The input data are (but not limited to) remote sensing observations (EUV images of the solar disk, Visible Light coronagraphic images, radio dynamic spectra, etc...), in situ plasma measurements (interplanetary plasma density, velocity, magnetic field, etc...), as well as measurements acquired by local sensors and detectors (radio antenna, fluxgate magnetometer, full-sky cameras, located in OATo). The output products are automatic identification, tracking, and monitoring of solar stationary and dynamic features near the Sun (coronal holes, active regions, coronal mass ejections, etc...), and in the interplanetary medium (shocks, plasmoids, corotating interaction regions, etc...), as well as reconstructions of the interplanetary medium where solar disturbances may propagate from the Sun to the Earth and beyond. These are based both on empirical models and numerical MHD simulations. The aim of SWELTO is not only to test new data analysis methods for future application for Space Weather monitoring and prediction purposes, but also to procure, test and deploy new ground-based instrumentation to monitor the ionospheric and geomagnetic responses to solar activity. Moreover, people involved in SWELTO are active in outreach to disseminate the topics related with Space Weather to students and the general public.

For the purpose of investigating the differential rotation of the solar corona, we analyzed ultraviolet (UV) spectral line observations acquired on both the east and west limbs at 1.7 $R_{\odot}$ by SOHO/UVCS during the solar minimum preceding solar cycle 23. To obtain a reliable and statistically robust picture of the rotational profile, we used a set of simultaneous 400-day long spectral line intensities of five different spectral lines: O VI 1032 A, O VI 1037 A, Si XII 499 A, Si XII 521 A, and H I 1216 A, which are routinely observed by UVCS. The data were analyzed by means of two different techniques: the generalized Lomb-Scargle periodogram (GLS) and a multivariate data-adaptive technique called multichannel singular spectrum analysis (MSSA). Among many other positive outcomes, this latter method is unique in its ability to recognize common oscillatory modes between the five time series observed at both limbs. The latitudinal rotation profile obtained in this work emphasizes that the low-latitude region of the UV corona (about $\pm 20^{\circ}$ from the solar equator) exhibits differential rotation, while the higher-latitude structures do rotate quasi-rigidly. The differential rotation rate of the solar corona as evinced at low-latitudes is consistent with the rotational profile of the near-surface convective zone of the Sun, suggesting that the rotation of the corona at 1.7 $R_{\odot}$ is linked to intermediate-scale magnetic bipole structures anchored near 0.99 $R_{\odot}$. The quasi-rigid rotation rate found at mid and high latitudes is instead attributed to the influence of large-scale coronal structures linked to the rigidly rotating coronal holes. We further suggest that the methodology presented in this paper could represent a milestone for future investigations on differential rotation rates when dealing with simultaneous multiwavelength data., Comment: A&A, in press (12 pages, 8 figures)

Context. Several physical properties of solar polar plumes have been identified by different published studies, however such studies are rare and sometimes in disagreement. Aims. The purpose of the present work is to analyze a set of SOHO/UVCS data dedicated to the observation of plumes and to obtain a picture of the physical properties of plumes in the intermediate solar corona through a self-consistent analysis. Methods. We applied the Doppler Dimming technique to data acquired by SOHO/UVCS in April 1996, which was during the very early phases of the mission. From this we derived outflow speeds and electron densities. We used SOHO/LASCO images as context data in order to better identify plume and interplume regions in the UVCS field of view. Results. The results we obtain demonstrate that in three cases out of four plumes expand with outflow speeds comparable to those of interplumes, and in a single case with lower speeds. We estimate that the contribution of plumes to the wind coming from the solar poles is about 20%, and that different plumes provide a different contribution, possibly according to different stages of their evolution. Conclusions. We conclude that plumes are not static structures, and that they contribute significantly to the wind coming from the solar poles., Comment: Astronomy & Astrophysics in press

The measurement of the lattice-parameter of silicon by x-ray interferometry assumes the use of strain-free crystals. This might not be the case because surface relaxation, reconstruction, and oxidation cause strains without the application of any external force. In a previous work, this intrinsic strain was estimated by a finite element analysis, where the surface stress was modeled by an elastic membrane having a 1 N/m tensile strength. The present paper quantities the surface stress by a density functional theory calculation. We found a value exceeding the nominal value used, which potentially affects the measurement accuracy.

Current sheets are important signatures of magnetic reconnection in the eruption of confined solar magnetic structures. Models of Coronal Mass Ejections (CMEs) involve formation of a current sheet connecting the ejected flux rope with the post eruption magnetic loops. Current sheets have been identified in white light images of CMEs as narrow rays trailing the outward moving CME core, and in ultraviolet spectra as narrow bright features emitting the Fe XVIII line. In this work samples of rays detected in white light images or in ultraviolet spectra have been analyzed. Temperatures, widths, and line intensities of the rays have been measured, and their correlation to the CME properties has been studied. The samples show a wide range of temperatures with hot, coronal and cool rays. In some cases, the UV spectra support the identification of rays as current sheets, but they show that some white light rays are cool material from the CME core. In many cases, both hot and cool material are present, but offset from each other along the UltraViolet Coronagraph Spectrometer (UVCS) slit. We find that about 18% of the white light rays show very hot gas consistent with the current sheet interpretation, while about 23% show cold gas that we attribute to cool prominence material draining back from the CME core. The remaining events have ordinary coronal temperatures, perhaps because they have relaxed back to a quiescent state., Comment: 15 pages, 11 figures, 2 tables. Accepted for publication in ApJ

The Sun is a non-equilibrium dissipative system subjected to an energy flow which originates in its core. Convective overshooting motions create temperature and velocity structures which show a temporal and spatial evolution. As a result, photospheric structures are generally considered to be the direct manifestation of convective plasma motions. The plasma flows on the photosphere govern the motion of single magnetic elements. These elements are arranged in typical patterns which are observed as a variety of multiscale magnetic patterns. High resolution magnetograms of quiet solar surface revealed the presence of magnetic underdense regions in the solar photosphere, commonly called voids, which may be considered a signature of the underlying convective structure. The analysis of such patterns paves the way for the investigation of all turbulent convective scales from granular to global. In order to address the question of magnetic structures driven by turbulent convection at granular and mesogranular scales we used a "voids" detection method. The computed voids distribution shows an exponential behavior at scales between 2 and 10 Mm and the absence of features at 5-10 Mm mesogranular scales. The absence of preferred scales of organization in the 2-10 Mm range supports the multiscale nature of flows on the solar surface and the absence of a mesogranular convective scale.

There are relatively few observations of UV emission during the impulsive phases of solar flares, so the nature of that emission is poorly known. Photons produced by solar flares can resonantly scatter off atoms and ions in the corona. Based on off-limb measurements by SOHO/UVCS, we derive the O VI $\lambda$1032 luminosities for 29 flares during the impulsive phase and the Ly$\alpha$ luminosities of 5 flares, and we compare them with X-ray luminosities from GOES measurements. The upper transition region and lower transition region luminosities of the events observed are comparable. They are also comparable to the luminosity of the X-ray emitting gas at the beginning of the flare, but after 10-15 minutes the X-ray luminosity usually dominates. In some cases we can use Doppler dimming to estimate flow speeds of the O VI emitting gas, and 5 events show speeds in the 40 to 80 $\rm km s^{-1}$ range. The O VI emission could originate in gas evaporating to fill the X-ray flare loops, in heated chromospheric gas at the footpoints, or in heated prominence material in the coronal mass ejection. All three sources may contribute in different events or even in a single event, and the relative timing of UV and X-ray brightness peaks, the flow speeds, and the total O VI luminosity favor each source in one or more events., Comment: 18 pages, 8 figures, 3 tables

Coronal plumes, which extend from solar coronal holes (CH) into the high corona and - possibly - into the solar wind (SW), can now continuously be studied with modern telescopes and spectrometers on spacecraft, in addition to investigations from the ground, in particular, during total eclipses. Despite the large amount of data available on these prominent features and related phenomena, many questions remained unanswered as to their generation and relative contributions to the high-speed streams emanating from CHs. An understanding of the processes of plume formation and evolution requires a better knowledge of the physical conditions at the base of CHs, in plumes and in the surrounding inter-plume regions (IPR). More specifically, information is needed on the magnetic field configuration, the electron densities and temperatures, effective ion temperatures, non-thermal motions, plume cross-sections relative to the size of a CH, the plasma bulk speeds, as well as any plume signatures in the SW. In spring 2007, the authors proposed a study on "Structure and dynamics of coronal plumes and inter-plume regions in solar coronal holes" to the International Space Science Institute (ISSI) in Bern to clarify some of these aspects by considering relevant observations and the extensive literature. This review summarizes the results and conclusions of the study. Stereoscopic observations allowed us to include three-dimensional reconstructions of plumes. Multi-instrument investigations carried out during several campaigns led to progress in some areas, such as plasma densities, temperatures, plume structure and the relation to other solar phenomena, but not all questions could be answered concerning the details of plume generation process(es) and interaction with the SW., Comment: To appear on: The Astronomy and Astrophysics Review. 72 pages, 30 figures

Pores are one of the various features forming in the photosphere by the emergence of magnetic field onto the solar surface. They lie at the border between tiny magnetic elements and larger sunspots. Light bridges, in such structures, are bright features separating umbral areas in two or more irregular regions. Commonly, light bridges indicate that a the merging of magnetic regions or, conversely, the breakup of the area is underway. We investigate the velocity structure of a solar pore (AR10812) with light bridge, and of the quiet solar photosphere nearby, analyzing high spatial and spectral resolution images. The pore area has been observed with the Interferometric BI-dimensional Spectrometer (IBIS) at the Dunn Solar Telescope, acquiring monochromatic images in the Ca II 854.2 nm line and in the Fe I 709.0 nm line as well as G-band and broad-band images. We also computed the Line of Sight (LoS) velocity field associated to the Fe I and Fe II photospheric lines. The amplitude of the LoS velocity fluctuations, inside the pore, is smaller than that observed in the quiet granulation near the active region. We computed the azimuthal average LoS velocity and derived its radial profile. The whole pore is characterized by a downward velocity -200 m/s and by an annular downflow structure with an average velocity of -350 m/s with respect to the nearby quiet sun. The light bridge inside the pore, when observed in the broad-band channel of IBIS and in the red wing of Ca II 854.2 nm line, shows an elongated dark structure running along its axis, that we explain with a semi-analytical model. In the highest resolution LoS velocity images the light bridge shows a profile consistent with a convective roll: a weak upflow, 50-100m/s, in correspondence of the dark lane, flanked by a downflow, -(200-300) m/s., Comment: 7 pages, 10 figures

The present spectroscopic study of the ultraviolet coronal emission in a polar hole, detected on April 6-9, 1996 with the Ultraviolet Coronagraph Spectrometer aboard the SOHO spacecraft, identifies the inter-plume lanes and background coronal hole regions as the channels where the fast solar wind is preferentially accelerated. In inter-plume lanes, at heliocentric distance 1.7 \rsun, the corona expands at a rate between 105 km/s and 150 km/s, that is, much faster than in plumes where the outflow velocity is between 0 km/s and 65 km/s. The wind velocity is inferred from the Doppler dimming of the O VI $\lambda\lambda$ 1032, 1037 \AA lines, within a range of values, whose lower and upper limit corresponds to anisotropic and isotropic velocity distribution of the oxygen coronal ions, respectively., Comment: 14 pages, 4 figures, 3 tables, Accepted by ApJ Letters

We have developed a detector, consisting of a cryogenic calorimeter with a scintillating crystal as absorber, and a second calorimeter for the detection of the scintillation light, both operated at 12 mK. Using a CaWO4 crystal with a mass of 6g as scintillating absorber, we have achieved a discrimination of nuclear recoils against electron recoils with a suppression factor of 99.7% at energies above 15 keV. This novel method will be applied for background rejection in the CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) experiment looking for dark matter Weakly Interacting Massive Particles (WIMPs)., Comment: 10 pages, 4 zipped figures (not good res.)