Project

Back to overview

NLTE calculations of the Solar Spectrum with Cross-Influence of Solar Atmospheric Structures

English title NLTE calculations of the Solar Spectrum with Cross-Influence of Solar Atmospheric Structures
Applicant Schmutz Werner
Number 157099
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 01.01.2015 - 31.12.2016
Approved amount 221'600.00
Show all

Keywords (5)

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

Lay Summary (French)

Lead
Le projet a pour but de calculer le spectre solaire de façon théorique en incluant les interactions entre les différentes structures présentes à sa surface. La température en fonction de la hauteur dans l'atmosphère diffère d'une région à l'autre, par exemple dans les taches solaires, les facules ou les régions non-magnétisées. Le transfert de radiation est généralement calculé pour ces régions de façon indépendante en considérant seulement leur profil de température respectif; le projet a pour but de modéliser la situation où des photons peuvent être transférés d'une structure à une autre, influençant ainsi le transfert de radiation à un endroit donné ainsi que les populations statistiques des divers niveaux atomiques.
Lay summary
Il a été démontré que les calculs du spectre solaire doivent tenir compte de la nature tri-dimensionnelle de la surface du Soleil. Les simulations complètes en trois dimensions incluant les effets magnétiques et hydrodynamiques sont trop exigeantes en termes numériques. Le but du projet est de développer une méthode hybride, peu coûteuse en temps de calcul, qui permettra de simuler les effets tri-dimensionnels dans le transfert de radiation, et donc de produire des spectres solaires plus réalistes que ceux présentement disponibles. Ils permettront de mieux comprendre la physique de son atmosphère, et possiblement de résoudre des questions reliées à sa composition.

Ces calculs sont nécessaires pour comprendre l'influence de la variabilité solaire sur le climat. En effet, l'irradiance solaire varie en fonction de son niveau d'activité magnétique, ce qui a un impact sur la haute atmosphère terrestre et possiblement, indirectement, à la surface. La modélisation climatique nécessite donc une excellente connaissance du spectre solaire et de sa variabilité.
Direct link to Lay Summary Last update: 07.01.2015

Responsible applicant and co-applicants

Employees

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
147659 Future and Past Solar Influence on the Terrestrial Climate II 01.01.2014 Sinergia
169647 NLTE calculations of the Solar Spectrum with Cross-Influence of Solar Atmospheric Structures. II Validation and Application 01.01.2017 Project funding (Div. I-III)
153301 Physical understaning of the solar irradiance at radio frequencies 01.04.2014 Project funding (Div. I-III)
153302 Variability of Solar Irradiance and its implications on the terrestrial middle atmosphere 01.04.2014 Project funding (Div. I-III)

Abstract

Even in its most quiet spot less state the Sun realizes its emergent flux with a distribution of solar atmospheric structures in millions of individual regions. Several investigations have demonstrated that an average 1-dimensional atmosphere cannot represent such a distribution - an adequate 1D atmosphere can only be defined for representing a restricted spectral range. Nevertheless, 1D solar atmospheres are widely used for the interpretation of stellar and solar spectra and for the interpretation of the solar spectral-irradiance variability 1D-atmospheres are the de-facto standards. The solar irradiance is combined from a handful of individual and independent 1D-structures, each representing an average solar activity feature. The resulting reconstruction of the total and spectral solar irradiance variability is surprisingly successful but a careful analysis still reveals shortcomings of this approach. The largest deficit is that not the full solar spectrum can be reproduced well. Simulations with 3D hydrodynamic codes indicate that the deficit is likely in the assumption of a single atmospheric structure instead of a 3D structure distribution as in reality on the Sun. One of the most important open questions in solar physics is the so-called oxygen crisis, which is understood to have its origin in the inadequate representation of the solar emergent flux by 1D models. On the other hand, a full 3D NLTE radiative transfer simulating the real Sun is technically not yet feasible. The innovative idea put forward into this proposal is a simplified approach using structure redistribution functions. The aim of the proposed project is to develop a new computer code that solves for non-local thermodynamic equilibrium of the level populations together with the solution of the radiation transfer simultaneously for a number of solar 1D atmospheric structures. The code will take into account the effects of the cross-influence between the components via the mean intensity at a given atmospheric depth point, which is a composite of weighted intensities of all included components. The result will by a emergent flux with contributions from all structures that are cross-influenced by each other. After the development of the code we will carefully investigate the effects of the cross-influence with emphasize on aspects that can be verified against observations. The project result after two years is a numerical tool for calculating the solar irradiance more realistically than presently possible. The computer code will be available for any interested scientist and will be used to address a number of solar problems in follow up projects.
-