Solar Irradiance et Planetary Atmospheres

Séminaire IPAG de Gaël Cessateur (PMOD/WRC), jeudi 25 septembre 2014 à 11h00, IPAG seminar room

The solar UV irradiance is one of a key parameters for space weather and space climate studies. Thorough several examples, I will show how the knowledge of the solar UV variability is of a great importance. I will also present a new model of solar irradiance variability for short term variations, COSIR for Code Of Solar Irradiance Reconstruction. Based on the assumption that the variability is triggered by the solar surface magnetism, we consider four types of active features such as sunspot umbra and penumbra, active network and faculae. The disk area coverages of these features have been deduced from the segmentation of solar magnetograms and solar images as provided by the HMI instrument onboard SDO. Spectra of active regions and the quiet Sun have been calculated with the radiative transfer code COSI. COSIR calculations are then directly compared with several SSI observations in the UV and visible spectral ranges. Model and observations are in excellent agreement for rotational variability, longer-term variations being however poorly constrained ans present significant differences. Others ways of comparison are then to be considered, either with direct observations with radiometers particularly suited for long term observations, or either with Sun-like stars observations.