Accurate temperature diagnostics of the solar corona are necessary for detecting the heating and cooling processes, and better understanding the conversion of the magnetic energy into thermal energy. A major obstacle in this enterprise is the multi-temperature emission contained in ultraviolet (UV) and extreme UV (EUV) passbands such as those of the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) and the Slit-Jaw Imager (SJI) of the Interface Region Imaging Spectrograph (IRIS). In this work we extend the Response Fitting (RFit) method to disambiguate between cool, warm, and hot emission in the SDO/AIA and IRIS/SJI passbands. We improve previous results for AIA 304 Å and find very good cool/hot decomposition for AIA 94 Å allowing to improve previous empirical disambiguation methods for this passband. The hot temperature coverage of AIA allows RFit to be applied across instruments. This allows to disambiguate the hot flaring emission from Fe xxi contained within the SJI 1330 Å and SJI 1400 Å passbands, supported by IRIS spectrograph (SG) results. We further estimate that the SJI 1330 Å response function lacks ≈ 50% of emission at temperatures above log T=7 . Photospheric abundances help reduce this gap to ≈ 40% . The emission peak at log T=6.2 in the SJI response functions is greatly altered at different densities, which can be used, in principle, for density diagnostics. These results are basically identical to those with the Differential Emission Measure (DEM) method, with the advantage that RFit is instantaneous, unlocking the possibility of real-time measurements. We also provide lower bounds for the hot emission in AIA 211 Å, and the very hot (flaring) emission in AIA 131 Å and AIA 193 Å, which help constrain the overestimated emission from the DEM in the hot temperature range. We apply RFit to an AIA-IRIS co-observation that includes a flare, and calculate the average relative percentage contribution for the cool-hot emission to find 17/83, 96/4, 79/21, 10/90, 65/35, 65/35, respectively for AIA 94 Å, AIA 131 Å, AIA 211 Å, AIA 304 Å, SJI 1330 Å and SJI 1400 Å. We obtain a more coherent picture of the hot temperature evolution in the log T =6.8 – 7.15 temperature range and its spatial localisation during the flare, and similarly for the cooling during the gradual phase. We further accurately detect and quantify the cool plasma from coronal rain, which is observed to increase seven-fold due to the flare-driven cooling.

We present the point-spread function (PSF) of the Extreme Ultraviolet High-Resolution Imager (HRIEUV) onboard Solar Orbiter, which observes the Sun at 174 Angstrom. This PSF provides a quantitative description of light diffracted by the mesh and mounting supporting the entrance filter, light diffracted by the mesh supporting the filter-wheel filter, as well as light that is diffusely scattered by the microroughness of the mirrors. Deconvolution with this PSF corrects the images for instrumental scattered light, substantially improving image quality and photometric accuracy. First, we determine the diffraction component of the PSF from mechanical drawings of the instrument. We find that 26

We report the first detection of a magnetic discontinuity in the upper solar chromosphere associated with a coronal loop brightening. Our findings are based on novel observations obtained by the Chromospheric LAyer SpectroPolarimeter (CLASP2.1) suborbital space experiment. During its short 6 minute flight, CLASP2.1 successfully obtained spectropolarimetric data across the Mg ii h and k lines, which allowed us to map the longitudinal magnetic field at multiple heights in the chromosphere of a solar active region. During our observation, we found a coronal loop brightening that was intermittently and recurrently heated. The temperature of the brightening plasma is above 2.5 MK, which is higher than the ambient temperature, and no corresponding brightening is detected in the images of the photosphere and lower chromosphere. The notable finding of our study is that the coronal loop brightening of interest is observed across a region where the magnetic field polarity changes abruptly in the upper chromosphere. Our results provide observational evidence that the heating mechanism of the coronal loop brightening is consistent with magnetic reconnection in the upper solar chromosphere.

The Solar and Heliospheric Observatory (SOHO) Extreme-ultraviolet Imaging Telescope (EIT) has been taking images of the Solar disk and corona in four narrow EUV bandpasses (171Å, 195Å, 284Å, and 304Å) at a minimum cadence of once per day since early 1996. The time series of fully-calibrated EIT images now spans approximately 28 years, from early 1996 to early 2024, covering solar cycles 23, 24, and the beginning of cycle 25. We convert this extensive EIT image archive into a time series of `Sun-as-a-star' light curves in EIT's four bandpasses, providing a long-term record of solar EUV variability. These Sun-as-a-star light curves, available for download from https://doi.org/10.5281/zenodo.15474179, trace the Sun as if it were a distant point source, viewed from a fixed perspective. We find that our EUV light curves trace the $\sim$ 11-year solar activity cycle and the $\sim$ 27-day rotation period much better than comparable optical observations. In particular, we can accurately recover the solar rotation period from our 284Ålight curve for 26 out of 28 calendar years of EIT observations (93% of the time), compared to only 3 out of 29 calendar years (10% of the time) of the VIRGO total solar irradiance time series, which is dominated by optical light. Our EIT light curves, in conjunction with Sun-as-a-star light curves at optical wavelengths, will be valuable to those interested in inferring the EUV/UV character of stars with long optical light curves but no intensive UV observations, as well as to those interested in long-term records of solar and space weather.

We determine magnetic fields from the photosphere to the upper chromosphere combining data from the Hinode satellite and the CLASP2.1 sounding rocket experiment. CLASP2.1 provided polarization profiles of the Mg |sc ii h and k lines, as well as of the Mn |sc i lines around 2800 |AA, across various magnetic structures in an active region, containing a plage, a pore, and the edges of a sunspot penumbra. By applying the Weak-Field Approximation (WFA) to the circular polarization profiles of these spectral lines, we obtain a longitudinal magnetic field map at three different heights in the chromosphere (lower, middle, and upper). This is complemented by data from Hinode (photospheric magnetic field), IRIS, and SDO (high-spatial-resolution observations of the chromosphere and corona). We quantify the height expansion of the plage magnetic fields and find that the magnetic fields expand significantly in the middle chromosphere, shaping the moss observed above in the transition region and corona. We identified an area with polarity reversal at the upper chromosphere around the edge of the pore, suggesting the presence of a magnetic discontinuity in the upper chromosphere. Transient and recurrent jet-like events are observed in this region, likely driven by magnetic reconnection. Around the penumbral edge, we find large-scale magnetic fields corresponding to the superpenumbral fibrils seen in the upper chromosphere. In the superpenumbral fibrils, we find Zeeman-induced linear polarization signals, suggesting the presence of a significantly inclined magnetic field, as strong as 1000 G in the upper chromosphere.

Context. The Solar and Heliospheric Observatory (SOHO) Extreme-ultraviolet Imaging Telescope (EIT) has been taking images of the solar disk and corona in four narrow extreme ultraviolet (EUV) bandpasses (171 angstrom, 195 angstrom, 284 angstrom, and 304 angstrom) at a minimum cadence of once per day since early 1996. The time series of fully calibrated EIT images now spans approximately 28 years, from early 1996 to early 2024, covering solar cycles 23 and 24 in their entirety, as well as the beginning of cycle 25. Aims. We aim to convert this extensive EIT image archive into a set of "Sun-as-a-star" light curves in EIT's four bandpasses, observing the Sun as if it were a distant point source viewed from a fixed perspective. Methods. To construct the light curves, we summed the flux in each EIT image into one flux value, with an uncertainty accounting for both the background noise in the image and the potential spillover of flux beyond the bounds of the image (which is especially important for the bands with significant coronal emission). We corrected for long-term instrumental systematic trends in the light curves by comparing our 304 angstrom light curve to the ultraviolet light curve taken by SOHO's CELIAS/SEM solar wind monitoring experiment, which has a very similar bandpass to the EIT 304 angstrom channel. We corrected for SOHO's viewing angle by fitting a trend to the flux values with respect to SOHO's heliocentric latitude at the time of each observation. Results. We produced two sets of Sun-as-a-star light curves with different uncertainty characteristics, available for download from Zenodo, either of which might be preferred for different types of future analyses. In version (1), we treated the EIT instrumental systematics consistently across the entire SOHO mission lifetime, producing a light curve with approximately homoscedastic uncertainties. In version (2), we only divided out the EIT instrumental systematics from November 12, 2008, onward; this is the point at which these systematics start to have a noticeable deleterious effect on the data. Therefore, version (2) has heteroscedastic uncertainties, but these uncertainties are much smaller than the version (1) uncertainties over the first half of the mission. Conclusions. We find that our EUV light curves trace the Sun's similar to 11-year solar activity cycle and similar to 27-day rotation period much better than comparable optical observations. In particular, we can accurately recover the solar rotation period from our 284 angstrom light curve for 26 out of 28 calendar years of EIT observations (93% of the time), compared to only 3 out of 29 calendar years (10% of the time) for the VIRGO total solar irradiance time series, which is dominated by optical light. Our EIT light curves, in conjunction with Sun-as-a-star light curves at optical wavelengths, will be valuable to those interested in inferring the EUV/UV character of stars with long optical light curves, but no intensive UV observations, as well as to those interested in long-term records of solar and space weather.

Context. Plasma upflows with a Doppler shift exceeding -10 km s(-1) at active region (AR) boundaries are considered potential sources of the nascent slow solar wind. These upflows are often located at the footpoints of large-scale fan-like loops and show temperature-dependent Doppler shifts with redshifts in the transition region and blueshifts in the lower corona. Aims. We investigate the driving mechanisms of a pair of coronal upflow regions on the western and eastern peripheries of an AR, which have different magnetic topologies and surroundings. It is aimed to explore how these upflows couple to the lower atmosphere. Methods. Using observations of the Fe XII 19.51 nm line from Hinode, we identified two upflow regions at the western and eastern boundaries of a decaying AR. Context images for the two regions were obtained by the High Resolution Imager (HRI) telescope of the Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter mission. Other instruments on Solar Orbiter and other observatories provide diagnostics to the lower atmosphere. Potential Field Source Surface (PFSS) extrapolations were used to examine the magnetic field configuration associated with the AR upflows. Results. The eastern upflow region, located over the AR moss, displays small-scale dynamic fibril structures, whereas the western region hosts fan-like loops. We found blueshifted Ne VIII emission at the eastern site, in contrast to redshifted Ne VIII profiles in the west. Magnetic field extrapolations reveal a pseudostreamer topology connecting both these regions. Moreover, low transition-region lines show systematically reduced redshift below the eastern footpoint. Conclusions. The observations support the scenario in which both upflows are driven by pressure imbalances created by coronal reconnection, leading to a continuous upflow above approximately 0.6 MK (i.e., Ne VIII line formation temperature). Meanwhile, mass flows in the lower transition region beneath the eastern upflow region appear to respond passively to the pressure-driven coronal upflows.

The magnetic fields and dynamical processes in the solar polar regions play a crucial role in the solar magnetic cycle and in supplying mass and energy to the fast solar wind, ultimately being vital in controlling solar activities and driving space weather. Despite numerous efforts to explore these regions, to date no imaging observations of the Sun's poles have been achieved from vantage points out of the ecliptic plane, leaving their behavior and evolution poorly understood. This observation gap has left three top-level scientific questions unanswered: How does the solar dynamo work and drive the solar magnetic cycle? What drives the fast solar wind? How do space weather processes globally originate from the Sun and propagate throughout the solar system? The Solar Polarorbit Observatory(SPO) mission, a solar polar exploration spacecraft, is proposed to address these three unanswered scientific questions by imaging the Sun's poles from high heliolatitudes. In order to achieve its scientific goals, SPO will carry six remote-sensing and four in-situ instruments to measure the vector magnetic fields and Doppler velocity fields in the photosphere, to observe the Sun in the extreme ultraviolet, X-ray, and radio wavelengths, to image the corona and the heliosphere up to 45 Rs, and to perform in-situ detection of magnetic fields,and low-and high-energy particles in the solar wind. The SPO mission is capable of providing critical vector magnetic fields and Doppler velocities of the polar regions to advance our understanding of the origin of the solar magnetic cycle, providing unprecedented imaging observations of the solar poles alongside in-situ measurements of charged particles and magnetic fields from high heliolatitudes to unveil the mass and energy supply that drive the fast solar wind, and providing observational constraints for improving our ability to model and predict the three-dimensional(3D) structures and propagation of space weather events.

The extreme-ultraviolet (EUV) brightenings identified by Solar Orbiter, commonly known as campfires, are the smallest transient brightenings detected to date outside active regions in the solar corona. We investigate the spatio-temporal distribution of a large ensemble of the finest-scale EUV transient brightenings observed by the Extreme Ultraviolet Imager (EUI) aboard Solar Orbiter. We perform a statistical analysis of the EUV brightenings by using quiet-Sun observations at the highest possible spatial resolution ever obtained by EUI. We use observations in the 17.4 nm passband of the High Resolution EUV Imager (HRIEUV) of EUI acquired during the closest perihelia of Solar Orbiter in 2022 and 2023. Solar Orbiter being at a distance 0.293 AU from the Sun, these observations have an exceptionally high image scale of 105 km, recorded at a fast cadence of 3 seconds. We use a wavelet-based automatic detection algorithm to detect and characterise the events of interest, and study their morphological and photometrical properties. We report the detection of smallest and shortest lived EUV brightenings to date in the quiet-Sun. The size and lifetime of the detected EUV brightenings appear power-law distributed down to a size of 0.01 Mm^2 and a lifetime of 3 seconds. In general their sizes lie in the range of 0.01 Mm^2 to 50 Mm^2 , and their lifetimes vary between 3 seconds and 40 minutes. We find an increasingly high number of EUV brightenings at smaller spatial and temporal scales. We estimate that about 3600 EUV brightenings appear per second on the whole Sun. The HRIEUV brightenings thus represent the most prevalent, localised and finest-scale transient EUV brightenings in the quiet regions of the solar corona.

The quiet Sun corona and coronal holes, as seen in the extreme ultraviolet (EUV), host a variety of phenomena that operate over a range of spatial and temporal scales. Dynamic brightenings and jets of at most a few megameters appear to evolve on minute timescales. Coronal structures larger than tens of Mm evolve on much longer, hour timescales. Understanding the characteristics of the quiet Sun corona and coronal holes along with their disparate phenomena will provide important constraints on models that aim to explain how the plasma is heated and how it further expands to form the solar wind. In 2020, the European Space Agency (ESA) Solar Orbiter mission was launched. It features a comprehensive remote-sensing package, which includes two instruments observing in the Extreme Ultraviolet (EUV) and UV spectrometer data: the Extreme Ultraviolet Imager (EUI) that provides high resolution Extreme Ultraviolet (EUV) images at 174 Å (HRIEUV), and the Spectral Imaging of the Coronal Environment (SPICE) spectrometer that enables plasma diagnostics, and the Polarimetric and Helioseismic Imager (PHI) that measures the photospheric magnetic field. These data, alongside a fleet of instruments on the Solar Dynamics Observatory (SDO), Hinode and the Interface Region Imaging Spectrograph (IRIS), are providing new information on the behaviour and dynamics of the quiet Sun and coronal holes. We will review the latest results and put them in context of describing the physics of coronal heating and solar wind formation.

The Chromospheric LAyer SpectroPolarimeter missions, CLASP2 and CLASP2.1, demonstrated that the near-UV spectral region between 279.30 and 280.68 nm is suitable for studying the magnetism of the solar chromosphere. In particular, the spectropolarimetric observations in the Mg ii h and k resonant doublet, Mn i 279.91 and 280.19 nm resonant lines, and Fe ii 279.79 and 280.66 nm lines acquired by these suborbital space experiments have been proven useful for inferring the magnetic field stratification in the solar chromosphere. However, several lines of the CLASP2/2.1 spectral region with significant circular polarization signals had remained unexplored. After identifying two Ni i (279.95 and 280.59 nm) lines, one Mn ii (280.62 nm) line, and one Fe i (280.53 nm) line, here we apply the weak-field approximation to the spectropolarimetric observations of active region plages by CLASP2 and CLASP2.1. By comparing the results with previous studies, we are able to estimate the formation heights of these CLASP2/2.1 additional spectral lines and to demonstrate their suitability to determine the magnetic field stratification from the photosphere to the upper chromosphere.

Context. The identification of large numbers of localised transient extreme ultraviolet (EUV) brightenings, on very small spatial scales, in the quiet Sun corona has been one of the key early results from Solar Orbiter. However, there are still a great deal of unknowns about these events. Aims. In this work, we aim to better understand EUV brightenings by investigating their spatial distributions. Specifically, we have investigated whether they occur co-spatially with specific line-of-sight (LoS) magnetic field topologies in the photospheric network. Methods. We detected the EUV brightenings in this work using an automated algorithm applied to a high-cadence (3 s) dataset sampled over similar to 30 minutes on 8 March 2022 by the Extreme Ultraviolet Imager's 17.4 nm EUV High Resolution Imager (HRIEUV). Data from the Solar Dynamics Observatory's Helioseismic and Magnetic Imager (SDO/HMI) and Atmospheric Imaging Assembly (SDO/AIA) were used to provide context on the LoS magnetic field and for alignment purposes, respectively. Results. We found a total of 5064 EUV brightenings within this dataset that are directly comparable to events reported previously in the literature. These events occurred within around 0.015-0.020% of pixels for any given frame. We compared eight different thresholds to split the EUV brightenings into four different categories related to the LoS magnetic field. Using our preferred threshold, we found that 627 EUV brightenings (12.4%) occurred co-spatially with strong bipolar configurations and 967 EUV brightenings (19.1%) occurred in weak field regions. Fewer than 10% of EUV brightenings occurred co-spatially with the unipolar LoS magnetic field, no matter what threshold was used. Of the 627 strong bipolar EUV Brightenings, 54 were found to occur co-spatially with cancellation, whilst 57 occurred co-spatially with emergence. Conclusions. EUV brightenings are primarily found to occur co-spatially with the strong LoS magnetic field in the photospheric network. However, they do not predominantly occur co-spatially with (cancelling) bi-poles.

The identification of large numbers of localised transient EUV brightenings, with small spatial scales, in the quiet-Sun corona has been one of the key early results from Solar Orbiter. However, much is still unknown about these events. Here, we aim to better understand EUV brightenings by investigating their spatial distributions, specifically whether they occur co-spatial with specific line-of-sight magnetic field topologies in the photospheric network. EUV brightenings are detected using an automated algorithm applied to a high-cadence (3 s) dataset sampled over 30 min on 8 March 2022 by the Extreme Ultraviolet Imager's 17.4 nm EUV High Resolution Imager. Data from the Solar Dynamics Observatory's Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly are used to provide context about the line-of-sight magnetic field and for alignment purposes. We found a total of 5064 EUV brightenings within this dataset that are directly comparable to events reported previously in the literature. These events occurred within around 0.015-0.020 given frame. We compared eight different thresholds to split the EUV brightenings into four different categories related to the line-of-sight magnetic field. Using our preferred threshold, we found that 627 EUV brightenings (12.4 and 967 EUV brightenings (19.1 field no matter what threshold was used. Of the 627 Strong Bipolar EUV Brightenings, 54 were found to occur co-spatial with cancellation whilst 57 occurred co-spatial with emergence. EUV brightenings preferentially occur co-spatial with the strong line-of-sight magnetic field in the photospheric network. They do not, though, predominantly occur co-spatial with (cancelling) bi-poles.

We apply the HanleRT Tenerife Inversion Code to the spectro-polarimetric observations obtained by the Chromospheric LAyer SpectroPolarimeter. This suborbital space experiment measured the variation with wavelength of the four Stokes parameters in the near-ultraviolet spectral region of the Mg II h & k lines over a solar disk area containing part of an active region plage and the edge of a sunspot penumbra. We infer the stratification of the temperature, the electron density, the line of-sight velocity, the micro-turbulent velocity, and the longitudinal component of the magnetic field from the observed intensity and circular polarization profiles. The inferred model atmosphere shows larger temperature and electron density in the plage and the superpenumbra regions than in the quiet regions. The shape of the plage region in terms of its brightness is similar to the pattern of the inferred longitudinal component of the magnetic field in the chromosphere, as well as to that of the overlying moss observed by AIA in the 171 A band, which suggests a similar magnetic origin for the heating in both the plage and the moss region. Moreover, this heating is particularly significant in the regions with larger inferred magnetic flux. In contrast, in the superpenumbra, the regions with larger electron density and temperature are usually found in between these regions with larger magnetic flux, suggesting that the details of the heating mechanism in the chromosphere of the superpenumbra may be different to those in the plage, but with the magnetic field still playing a key role.

The AIA~304 channel on board the \textit{Solar Dynamics Observatory} (SDO) offers a unique view of low transition region (TR) plasma emitting in the He II 304 ˚A line. However, when observing off-limb, the emission of the (small) cool structures in the solar atmosphere (such as spicules, coronal rain and prominence material) can be of the same order as the surrounding hot coronal emission from other spectral lines included in the 304 passband, particularly over active regions. In this paper we investigate three methods based on temperature and morphology that are able to distinguish the cool and hot emission within the 304 passband. The methods are based on the Differential Emission Measure (DEM), a linear decomposition of the AIA response functions (RFit) and the Blind Source Separation (BSS) technique. All three methods are found to produce satisfactory results in both quiescent and flaring conditions, largely removing the diffuse corona and leading to images with cool material off-limb in sharp contrast with the background. We compare our results with co-aligned IRIS data in the SJI 1400 and 2796 channels, and find the RFit method to best match the quantity and evolution of the cool material detected with \textit{IRIS}. Some differences can appear due to plasma emitting in the log T = 5.1 − 5.5 temperature range, particularly during the catastrophic cooling stage prior to rain appearance during flares. These methods are in principle applicable to any passband from any instrument suffering from similar cool and hot emission ambiguity as long as there is good coverage of the hot temperature range.

Particle acceleration, and the thermalisation of energetic particles, are fundamental processes across the universe. Whilst the Sun is an excellent object to study this phenomenon, since it is the most energetic particle accelerator in the Solar System, this phenomenon arises in many other astrophysical objects, such as active galactic nuclei, black holes, neutron stars, gamma ray bursts, solar and stellar coronae, accretion disks and planetary magnetospheres. Observations in the Extreme Ultraviolet (EUV) are essential for these studies but can only be made from space. Current spectrographs operating in the EUV use an entrance slit and cover the required field of view using a scanning mechanism. This results in a relatively slow image cadence in the order of minutes to capture inherently rapid and transient processes, and/or in the spectrograph slit ‘missing the action’. The application of image slicers for EUV integral field spectrographs is therefore revolutionary. The development of this technology will enable the observations of EUV spectra from an entire 2D field of view in seconds, over two orders of magnitude faster than what is currently possible. The Spectral Imaging of the Solar Atmosphere (SISA) instrument is the first integral field spectrograph proposed for observations at ∼180 Å combining the image slicer technology and curved diffraction gratings in a highly efficient and compact layout, while providing important spectroscopic diagnostics for the characterisation of solar coronal and flare plasmas. SISA’s characteristics, main challenges, and the on-going activities to enable the image slicer technology for EUV applications are presented in this paper.

We present an analysis of the first connection mosaic made by the SPICE instrument on board the ESA / NASA Solar Orbiter mission on March 2, 2022. The data will be used to map coronal composition that will be compared with in-situ measurements taken by SWA/HIS to establish the coronal origin of the solar wind plasma observed at Solar Orbiter. The SPICE spectral lines were chosen to have varying sensitivity to the first ionization potential (FIP) effect, and therefore the radiances of the spectral lines will vary significantly depending on whether the elemental composition is coronal or photospheric. We investigate the link between the behavior of sulfur and the hypothesis that Alfvén waves drive FIP fractionation above the chromosphere. We performed temperature diagnostics using line ratios and emission measure (EM) loci, and computed relative FIP biases using three different approaches (two-line ratio (2LR), ratios of linear combinations of spectral lines (LCR), and differential emission measure (DEM) inversion) in order to perform composition diagnostics in the corona. We then compared the SPICE composition analysis and EUI data of the potential solar wind source regions to the SWA / HIS data products. Radiance maps were extracted from SPICE spectral data cubes, with values matching previous observations. We find isothermal plasma of around $LogT=5.8$ for the AR loops targeted, and that higher FIP-bias values are present at the footpoints of the coronal loops associated with two ARs. Comparing the results with the SWA/HIS data products encourages us to think that Solar Orbiter was connected to a source of slow solar wind during this observation campaign. black We demonstrate FIP fractionation in observations of the upper chromosphere and transition region emphasized by the behavior of the intermediate-FIP element sulfur.

This Letter reports the first observation of the onset of fully developed turbulence in the solar corona. Long time series of white-light coronal images, acquired by Metis aboard Solar Orbiter at 2 minutes cadence and spanning about 10 hr, were studied to gain insight into the statistical properties of fluctuations in the density of the coronal plasma in the time domain. From pixel-by-pixel spectral frequency analysis in the whole Metis field of view, the scaling exponents of plasma fluctuations were derived. The results show that, over timescales ranging from 1 to 10 hr and corresponding to the photospheric mesogranulation-driven dynamics, the density spectra become shallower moving away from the Sun, resembling a Kolmogorov-like spectrum at 3 R circle dot. According to the latest observation and interpretive work, the observed 5/3 scaling law for density fluctuations is indicative of the onset of fully developed turbulence in the corona. Metis observation-based evidence for a Kolmogorov turbulent form of the fluctuating density spectrum casts light on the evolution of 2D turbulence in the early stages of its upward transport from the low corona.

Coronal loops are the fundamental building blocks of the solar corona. Therefore, comprehending their properties is essential in unraveling the dynamics of the upper solar atmosphere. In this study, we conduct a comparative analysis of the morphology and dynamics of a coronal loop observed from two different spacecraft: the High Resolution Imager (HRIEUV) of the Extreme Ultraviolet Imager on board the Solar Orbiter, and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory. These spacecraft were separated by 43° during this observation. The main findings of this study are that (1) the observed loop exhibits similar widths in both the HRIEUV and AIA data, suggesting that the cross-sectional shape of the loop is circular; (2) the loop maintains a uniform width along its entire length, supporting the notion that coronal loops do not exhibit expansion; and (3) notably, the loop undergoes unconventional dynamics, including thread separation and abrupt downward movement. Intriguingly, these dynamic features also appear similar in data from both spacecraft. Although based on observation of a single loop, these results raise questions about the validity of the coronal-veil hypothesis and underscore the intricate and diverse nature of the complexity within coronal loops.