Exploiting solar visible-range observations by inversion techniques: from flows in the solar subsurface to a flaring atmosphere

Observations of the Sun in the visible spectral range belong to standard measurements obtained by instruments both on the ground and in the space. Nowadays, both nearly continuous full-disc observations with medium resolution and dedicated campaigns of high spatial, spectral and/or temporal resolution constitute a holy grail for studies that can capture (both) the long- and short-term changes in the dynamics and energetics of the solar atmosphere. Observations of photospheric spectral lines allow us to estimate not only the intensity at small regions, but also various derived data products, such as the Doppler velocity and/or the components of the magnetic field vector. We show that these measurements contain not only direct information about the dynamics of solar plasmas at the surface of the Sun but also imprints of regions below and above it. Here, we discuss two examples: First, the local time-distance helioseismology as a tool for plasma dynamic diagnostics in the near subsurface and second, the determination of the solar atmosphere structure during flares. The methodology in both cases involves the technique of inverse modelling.Comment: 29 pages, 15 figures. Accepted for publication in the book "Reviews in Frontiers of Modern Astrophysics: From Space Debris to Cosmology" (eds Kabath, Jones and Skarka; publisher Springer Nature) funded by the European Union Erasmus+ Strategic Partnership grant "Per Aspera Ad Astra Simul" 2017-1-CZ01-KA203-03556

The European Solar Telescope

The European Solar Telescope (EST) is a project aimed at studying the magnetic connectivity of the solar atmosphere, from the deep photosphere to the upper chromosphere. Its design combines the knowledge and expertise gathered by the European solar physics community during the construction and operation of state-of-the-art solar telescopes operating in visible and near-infrared wavelengths: the Swedish 1m Solar Telescope, the German Vacuum Tower Telescope and GREGOR, the French Télescope Héliographique pour l’Étude du Magnétisme et des Instabilités Solaires, and the Dutch Open Telescope. With its 4.2 m primary mirror and an open configuration, EST will become the most powerful European ground-based facility to study the Sun in the coming decades in the visible and near-infrared bands. EST uses the most innovative technological advances: the first adaptive secondary mirror ever used in a solar telescope, a complex multi-conjugate adaptive optics with deformable mirrors that form part of the optical design in a natural way, a polarimetrically compensated telescope design that eliminates the complex temporal variation and wavelength dependence of the telescope Mueller matrix, and an instrument suite containing several (etalon-based) tunable imaging spectropolarimeters and several integral field unit spectropolarimeters. This publication summarises some fundamental science questions that can be addressed with the telescope, together with a complete description of its major subsystems

Effect of organic amendment on soil fertility and plant nutrients in a post-fire Mediterranean ecosystem

International audienceBackgrounds and aims In Mediterranean frequentlyburnt areas, the decrease of soil fertility leads to regressivevegetation dynamics. Organic amendments couldhelp to accelerate post-fire ecosystem resilience, byimproving soil properties and plant nutrition. This studywas conducted to assess the potential of a compostedbiosolid to restore an early post-fire shrubland.Methods About 50Mg.ha−1 of fresh co-composted sewagesludge and green wastes were surface applied7 months after fire on a silty-clayey soil. We monitoredover a 2-year period organic matter and nutrient transfersto soil, nutrient responses of dominant plant species,and ecosystem contamination by potentially toxic traceelements.Results Over the experimental survey, compost rapidlyand durably improved soil P2O5,MgO and K2O content,and temporarily increased N-(NO3− + NO2−) content.Plant nutrition was improved more or less durably dependingspecies. The most positive compost effect wason plant and soil phosphorus content. Plant nutrientstorage was not improved 2 years after amendment,suggesting luxury consumption. No contamination bytrace elements was detected in soil and plant.Conclusions The use of compost after fire could helpfor rapidly restoring soil fertility and improving plantnutrition. The increase of soil nutrient pools afteramendment emphazised the diversity of plant nutritionaltraits. Eutrophication risk could occur from high compostand soil P2O5 content