Abstract
This article describes an update of the physical models that we use to reconstruct the FUV and EUV irradiance spectra and the radiance spectra of the features that at any given point in time may cover the solar disk depending on the state of solar activity. The present update introduces important modifications to the chromosphere–corona transition region of all models. Also, the update introduces improved and extended atomic data. By these changes, the agreement of the computed and observed spectra is largely improved in many EUV lines important for the modeling of the Earth’s upper atmosphere. This article describes the improvements and shows detailed comparisons with EUV/FUV radiance and irradiance measurements. The solar spectral irradiance from these models at wavelengths longer than ≈ 200 nm is discussed in a separate article.
Highlights
Spectra and images of the solar disk are used by Fontenla et al (1999, 2009a, 2011, hereafter Articles 1, 2, and 3, respectively) to construct a set of models for the characteristic features of the solar atmosphere present on the disk throughout the solar cycle
We have shown a set of physical models and comparisons between the computed and observed spectra that show that a semi-empirical set of models can account for the observed EUV solar spectral irradiance (SSI) and its variation with solar activity
It should be kept in mind that including more components would only improve the description of solar activity if there were a way to determine daily the mix of components from solar images, and if their radiative interaction were either negligible or accounted for
Summary
Spectra and images of the solar disk are used by Fontenla et al (1999, 2009a, 2011, hereafter Articles 1, 2, and 3, respectively) to construct a set of models for the characteristic features of the solar atmosphere present on the disk throughout the solar cycle. This article compares calculations with key spectral features observed from space and shows that the present simple (one-dimensional, steady) models of mid-resolution areas of the solar surface, ≈ 2×2 arcsec, provide a fairly good representation of the SSI. The Ca II K images can be used, these do not directly provide information on the high-temperature components responsible for the UV and require some speculative assessment We currently use both chromospheric and coronal images to discriminate between the features on the disk and be able to assign these features to atmospheric models. UV spectral irradiance data are provided by the Solar Stellar Irradiance Comparison Experiment (SOLSTICE) instrument onboard the Solar Radiation and Climate Experiment (SORCE) satellite, and by the EUV Variability Experiment (EVE) instrument onboard the SDO satellite
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