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NLTE calculations of the Solar Spectrum with Cross-Influence of Solar Atmospheric Structures. II Validation and Application

English title NLTE calculations of the Solar Spectrum with Cross-Influence of Solar Atmospheric Structures. II Validation and Application
Applicant Schmutz Werner
Number 169647
Funding scheme Project funding (Div. I-III)
Research institution Physikalisch-Meteorologisches Observatorium Davos und Weltstrahlungszentrum
Institution of higher education Physikal.-Meteorolog. Observatorium Davos - PMOD
Main discipline Astronomy, Astrophysics and Space Sciences
Start/End 01.01.2017 - 30.09.2018
Approved amount 203'065.00
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Keywords (6)

space weather; sun-climate connection; solar physics; astrophysics; solar irradiance; solar chromospere

Lay Summary (French)

Lead
Les différentes couches de l'atmosphère solaire sont hautement inhomogènes et présentent un grand nombre de structures ayant différentes intensités émergentes. Le spectre du Soleil non magnétisé est généralement calculé en utilisant une structure simplifiée visant à reproduire les propriétés moyennes de l'atmosphère. Bien que cette approximation donne d'excellents résultats, certains aspects demeurent problématiques. Parmi les problèmes rencontrés, on retrouve 1) l'impossibilité de reproduire adéquatement le spectre solaire observé pour toutes les longueurs d'ondes en utilisant une structure atmosphérique moyenne et 2) le désaccord entre les abondances d'oxygène solaire dérivées avec les calculs unidimensionnel et tridimensionnel.
Lay summary
La solution à ces problèmes serait potentiellement atteinte en utilisant un modèle de transfert radiatif combiné aux calculs de magnétohydrodynamique, tout en considérant le régime hors équilibre thermodynamique local (hors ETL). Toutefois, ces calculs sont trop exigents en temps de calcul pour être effectués sur tout le spectre solaire. Le présent projet a pour but de contourner la difficulté des calculs tridimensionnels hors ETL en utilisant des calculs unidimensionnels hors ETL pour différentes structures, représentant la distribution statistique des diverses régions en utilisant un petit nombre de structures représentatives du Soleil non magnétisé. Pour ce projet, la géométrie est simplifiée en supposant une distribution homogène des structures sur la surface solaire. Ces dernières interagissent via l'introduction d'une fonction de distribution des structures. Ainsi, les calculs en régime hors ETL peuvent être effectués en un temps raisonnable tout en approximant les variations spatiales et temporelles de la distribution des caractéristiques de surface du Soleil non magnétisé. Ceci peut être effectué avec le code SOCRAT.
Direct link to Lay Summary Last update: 23.01.2017

Responsible applicant and co-applicants

Employees

Publications

Publication
NLTE Calculations of the Solar Spectrum Using Cross-Influence of Solar Atmosphere Structures
GuerreiroNuno, SchmutzWerner (2018), NLTE Calculations of the Solar Spectrum Using Cross-Influence of Solar Atmosphere Structures, PMOD/WRC, Davos, Switzerland.

Collaboration

Group / person Country
Types of collaboration
Max-Planck-Institut für Sonnensystemforschung in Göttingen Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication

Associated projects

Number Title Start Funding scheme
153302 Variability of Solar Irradiance and its implications on the terrestrial middle atmosphere 01.04.2014 Project funding (Div. I-III)
157099 NLTE calculations of the Solar Spectrum with Cross-Influence of Solar Atmospheric Structures 01.01.2015 Project funding (Div. I-III)
153301 Physical understaning of the solar irradiance at radio frequencies 01.04.2014 Project funding (Div. I-III)
147659 Future and Past Solar Influence on the Terrestrial Climate II 01.01.2014 Sinergia

Abstract

The solar atmosphere is highly inhomogeneous and shows a great variety of structures with different intensities, independently of the phase of the solar magnetic cycle. Typically, the calculation of the quiet solar spectrum is performed using a simplified structure supposedly representing the average properties of the atmosphere. Recent studies using 3D hydrodynamical simulations coupled with NLTE radiative transfer suggest that the 1D assumption is responsible for important shortcomings in determining solar properties. One such shortcoming is the disagreement in the solar oxygen abundance between the one obtained through 1D and 3D modeling. It is also well known that a specific average atmospheric structure do not allow to reproduce the entire solar spectrum equally well at all wavelengths. However, calculations in 3D and in NLTE are still computationally too expensive to be performed for the entire solar spectrum. The proposed project aims to compute a realistic simulation of the quiet Sun in NLTE with a simplified approach for accounting for the inhomogeneity: Instead of modeling the real distribution of structures we introduce a Solar Structure Distribution function, which will allow us to account for the simultaneous influence of different structures in a 1D radiation transport computation. We simplify the geometry by having a (relatively small) number of structures representing the observed distribution function of solar features and allowing each of them to interact with the others by taking into account the intensity coming from neighboring structures in the statistical population equations in each structure. The idea is that their distribution is not only representative of the spatial 3D configuration but also representing their temporal variations, hence approximating the spatial and temporal variation (of the order of a granule's lifetime) of the quiet Sun features distribution. With a Solar Structure Distribution function, the NLTE computations can be performed in a very reasonable amount of time. We expect to have a working code at our disposition from the currently ongoing precursor project at the beginning of the project and we will in the first year compare the results from our xD approach to 1.5D and 3D simulations done at Max Planck institute for Solar System research. The focus of the second year will then be on applying our code to sensitivity analyses to assess the effect of cross-influence on still unresolved solar problems, such as the missing UV opacity and most interestingly, on the determination of the oxygen abundance.
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