Context. We present the results for the in-flight radiometric calibration performed for the Visible Light (VL) channel of the Metis coronagraph on board Solar Orbiter. Aims. The radiometric calibration is a fundamental step in building the official pipeline of the instrument, devoted to producing the calibrated data in physical units (L2 data). Methods. To obtain the radiometric calibration factor ( ϵ VL ), we used stellar targets transiting the Metis field of view. We derived ϵ VL by determining the signal of each calibration star by means of the aperture photometry and calculating its expected flux in the Metis band pass. The analyzed data set covers the time range from the beginning of the Cruise Phase of the mission (June 2020) until March 2021. Results. Considering the uncertainties, the estimated factor ϵ VL is in a good agreement with that obtained during the on-ground calibration campaign. This implies that up to March 2021 there was no measurable reduction in the VL channel throughput. Finally, we compared the total and polarized brightness visible light images of the solar corona acquired with Metis and STEREO-A/COR2 during the November 2020 superior conjunction of these instruments. A general good agreement was obtained between the images of these instruments for both the total and polarized brightness.

On-board the Solar Orbiter ESA/NASA mission there is Metis, a coronagraph designed to study the solar corona by providing an artificial solar eclipse.Metis features two channels working at the ultraviolet Lyman-α (121.6 nm) and in the visible light (580-640 nm).On-ground, the Metis radiometric performance has been tested using a flat-field panel (uniform illumination); the stability of the performance can be verified in-flight through the analysis of the stars passing in the Metis Field of View.Care must be taken to ensure the quality of the calibration, both before launch and for the long period associated with the space mission lifetime.For this reason, we are carrying out long period research of stars that cross the Field of View of Metis.In this paper, we describe the vignetting function acquired: on-ground, simulated via a raytracing code and in-flight derived from on-ground measurements (performing some adjustments to account for the real Metis flight configuration).These vignetting functions are then compared with the vignetting data derived from the passage of the star Theta Ophiuchi in

Metis is the coronagraph on board the Solar Orbiter ESA/NASA mission, it is designed to study the solar corona by providing an artificial solar eclipse. Metis features two channels: the ultraviolet H I (121.6 nm) and the visible light (580-640 nm). This work is focalised on the latter. Radiometric performances have been tested on-ground using a flatfield panel (uniform illumination), and the in-flight stability can be verified through the light reflected from the instrument door. When the Sun light impacts on the spacecraft shield, a fraction is reflected in the direction of the door, which then partly reflects it inside Metis. The analysis of the door images confirms its integrity and that of its subsequent optical components, since the reflected intensity follows as expected a 1/r2 law, r being the Sun-spacecraft distance. Further analysis is being performed on such images to verify the operating status of various elements of Metis. Complementary ray-tracing simulation studies on the door retro-reflectivity properties are also in progress.

The Metis coronagraph is one of the remote sensing instruments hosted on board the ESA/NASA Solar Orbiter mission. Metis is devoted to carry out the first simultaneous imaging of the solar corona in both visible light (VL) and ultraviolet (UV). High-energy particles penetrate spacecraft materials and may limit the performance of on-board instruments. A study of galactic cosmic-ray (GCR) tracks observed in the first VL images gathered by Metis during the commissioning phase for a total of 60 seconds of exposure time is presented here. A similar analysis is planned for the UV channel. A prediction of the GCR flux up to hundreds of GeV is made here for the first part of the Solar Orbiter mission to study the Metis coronagraph performance. GCR model predictions are compared to observations gathered on board Solar Orbiter by the EPD/HET experiment in the range 10 MeV-100 MeV in the summer 2020 and with previous measurements. Estimated cosmic-ray fluxes above 70 MeV n^-1 have been also parameterized and used for Monte Carlo simulations aiming at reproducing the cosmic-ray track observations in the Metis coronagraph VL images. The same parameterizations can also be used to study the performance of other detectors. By comparing observations of cosmic-ray tracks in the Metis VL images with FLUKA Monte Carlo simulations of cosmic-ray interactions in the VL detector, it is found that cosmic rays fire a fraction of the order of 10^-4 of the whole image pixel sample. Therefore, cosmic rays do not affect sensibly the quality of Metis VL images. It is also found that the overall efficiency for cosmic-ray identification in the Metis VL images is approximately equal to the contribution of Z>2 particles. As a result, the Metis coronagraph may play the role of a proton monitor for long-term GCR variations during the overall mission duration.

Solar Orbiter, launched on February 9th 2020, is an ESA/NASA mission conceived to study the Sun. This work presents the embedded Metis coronagraph and its on-ground calibration in the 580-640 nm wavelength range using a flat field panel. It provides a uniform illumination to evaluate the response of each pixel of the detector; and to characterize the Field of View (FoV) of the coronagraph. Different images with different exposure times were acquired during the on-ground calibration campaign. They were analyzed to verify the linearity response of the instrument and the requirements for the FoV: the maximum area of the sky that Metis can acquire.

In this work, we present an investigation of the wind in the solar corona that has been initiated by observations of the resonantly scattered ultraviolet emission of the coronal plasma obtained with UVCS-SOHO, designed to measure the wind outflow speed by applying Doppler dimming diagnostics. Metis on Solar Orbiter complements the UVCS spectroscopic observations that were performed during solar activity cycle 23 by simultaneously imaging the polarized visible light and the H I Lyman- α corona in order to obtain high spatial and temporal resolution maps of the outward velocity of the continuously expanding solar atmosphere. The Metis observations, taken on May 15, 2020, provide the first H I Lyman- α 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 ultraviolet H I Ly α (121.6 nm) coronal emissions, obtained with the two Metis channels, were 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 was then derived as a function of the measured Doppler dimming. The static corona UV emission was 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° wide, centered on the extension of a quiet equatorial streamer present at the east limb – the coronal origin of the heliospheric current sheet – where the slowest wind flows at about 160 ± 18 km s −1 from 4 R ⊙ to 6 R ⊙ . Beyond the boundaries of the high-density layer, the wind velocity rapidly increases, marking the transition between slow and fast wind in the corona.

Context. The Solar Orbiter spacecraft will be equipped with a wide range of remote-sensing (RS) and in situ (IS) instruments to record novel and unprecedented measurements of the solar atmosphere and the inner heliosphere. To take full advantage of these new datasets, tools and techniques must be developed to ease multi-instrument and multi-spacecraft studies. In particular the currently inaccessible low solar corona below two solar radii can only be observed remotely. Furthermore techniques must be used to retrieve coronal plasma properties in time and in three dimensional (3D) space. Solar Orbiter will run complex observation campaigns that provide interesting opportunities to maximise the likelihood of linking IS data to their source region near the Sun. Several RS instruments can be directed to specific targets situated on the solar disk just days before data acquisition. To compare IS and RS, data we must improve our understanding of how heliospheric probes magnetically connect to the solar disk.Aims. The aim of the present paper is to briefly review how the current modelling of the Sun and its atmosphere can support Solar Orbiter science. We describe the results of a community-led effort by European Space Agency's Modelling and Data Analysis Working Group (MADAWG) to develop different models, tools, and techniques deemed necessary to test different theories for the physical processes that may occur in the solar plasma. The focus here is on the large scales and little is described with regards to kinetic processes. To exploit future IS and RS data fully, many techniques have been adapted to model the evolving 3D solar magneto-plasma from the solar interior to the solar wind. A particular focus in the paper is placed on techniques that can estimate how Solar Orbiter will connect magnetically through the complex coronal magnetic fields to various photospheric and coronal features in support of spacecraft operations and future scientific studies.Methods. Recent missions such as STEREO, provided great opportunities for RS, IS, and multi-spacecraft studies. We summarise the achievements and highlight the challenges faced during these investigations, many of which motivated the Solar Orbiter mission. We present the new tools and techniques developed by the MADAWG to support the science operations and the analysis of the data from the many instruments on Solar Orbiter.Results. This article reviews current modelling and tool developments that ease the comparison of model results with RS and IS data made available by current and upcoming missions. It also describes the modelling strategy to support the science operations and subsequent exploitation of Solar Orbiter data in order to maximise the scientific output of the mission.Conclusions. The on-going community effort presented in this paper has provided new models and tools necessary to support mission operations as well as the science exploitation of the Solar Orbiter data. The tools and techniques will no doubt evolve significantly as we refine our procedure and methodology during the first year of operations of this highly promising mission.

Context. To meet the scientific objectives of the mission, the Solar Orbiter spacecraft carries a suite of in-situ (IS) and remote sensing (RS) instruments designed for joint operations with inter-instrument communication capabilities. Indeed, previous missions have shown that the Sun (imaged by the RS instruments) and the heliosphere (mainly sampled by the IS instruments) should be considered as an integrated system rather than separate entities. Many of the advances expected from Solar Orbiter rely on this synergistic approach between IS and RS measurements. Aims. Many aspects of hardware development, integration, testing, and operations are common to two or more RS instruments. In this paper, we describe the coordination effort initiated from the early mission phases by the Remote Sensing Working Group. We review the scientific goals and challenges, and give an overview of the technical solutions devised to successfully operate these instruments together. Methods. A major constraint for the RS instruments is the limited telemetry (TM) bandwidth of the Solar Orbiter deep-space mission compared to missions in Earth orbit. Hence, many of the strategies developed to maximise the scientific return from these instruments revolve around the optimisation of TM usage, relying for example on onboard autonomy for data processing, compression, and selection for downlink. The planning process itself has been optimised to alleviate the dynamic nature of the targets, and an inter-instrument communication scheme has been implemented which can be used to autonomously alter the observing modes. We also outline the plans for in-flight cross-calibration, which will be essential to the joint data reduction and analysis. Results. The RS instrument package on Solar Orbiter will carry out comprehensive measurements from the solar interior to the inner heliosphere. Thanks to the close coordination between the instrument teams and the European Space Agency, several challenges specific to the RS suite were identified and addressed in a timely manner.

Metis is the coronagraph on board Solar Orbiter, the ESA mission devoted to the study of the Sun that will be launched in October 2018. Metis is designed to perform imaging of the solar corona in the UV at 121.6 nm and in the visible range where it will accomplish polarimetry studies thanks to a variable retarder plate. Due to mission constraints, the telemetry downlink on the spacecraft will be limited and data will be downloaded with delays that could reach, in the worst case, several months. In order to have a quick overview on the ongoing operations and to check the safety of the 10 instruments on board, a high-priority downlink channel has been foreseen to download a restricted amount of data. These so-called Low Latency Data will be downloaded daily and, since they could trigger possible actions, they have to be quickly processed on ground as soon as they are delivered. To do so, a proper processing pipeline has to be developed by each instrument. This tool will then be integrated in a single system at the ESA Science Operation Center that will receive the downloaded data by the Mission Operation Center. This paper will provide a brief overview of the on board processing and data produced by Metis and it will describe the proxy-pipeline currently under development to deal with the Metis low-latency data.

There are three major issues in modeling solar evanescent oscillations: the variation of the intensity [I]–velocity [V] phase difference of p-modes close to the base of photosphere; the existence of a plateau of negative I–V phase differences below and between the ridges of the low-frequency p-modes; the explanation of the I–V cross-spectra of the evanescent oscillations. We present new interpretations for the first two issues, based on modeling intensity fluctuations taking steep temperature gradients, opacity, and non-adiabatic cooling into account.

The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) is designed to study oscillations and the mag- netic field in the solar photosphere. It observes the full solar disk in the Fe I absorption line at 6173\AA . We use the output of a high-resolution 3D, time- dependent, radiation-hydrodynamic simulation based on the CO5BOLD code to calculate profiles F({\lambda},x,y,t) for the Fe I 6173{\AA} line. The emerging profiles F({\lambda},x,y,t) are multiplied by a representative set of HMI filter transmission profiles R_i({\lambda},1 \leq i \leq 6) and filtergrams I_i(x,y,t;1 \leq i \leq 6) are constructed for six wavelengths. Doppler velocities V_HMI(x,y,t) are determined from these filtergrams using a simplified version of the HMI pipeline. The Doppler velocities are correlated with the original velocities in the simulated atmosphere. The cross- correlation peaks near 100 km, suggesting that the HMI Doppler velocity signal is formed rather low in the solar atmosphere. The same analysis is performed for the SOHO/MDI Ni I line at 6768\AA . The MDI Doppler signal is formed slightly higher at around 125 km. Taking into account the limited spatial resolution of the instruments, the apparent formation height of both the HMI and MDI Doppler signal increases by 40 to 50 km. We also study how uncertainties in the HMI filter-transmission profiles affect the calculated velocities.

In our studies of the dynamics and energetics of the solar atmosphere, we have detected, in high-quality observations from Hinode SOT/NFI, ubiquitous small-scale upflows which move horizontally with supersonic velocities in the quiet Sun. We present the properties of these fast moving upflows (FMUs) and discuss different interpretations.