SPAM: Solar Spectrum Prediction for Applications and Modeling

Abstract

Solar Spectrum Prediction for Applications and Modeling (SPAM) is a new empirical model of solar X-ray, extreme ultraviolet and far ultraviolet radiation flux at the top of the Earth’s atmosphere. The model is based on 14 years of daily averaged TIMED spacecraft measurements from 2002 to 2016, when its sensors were regularly calibrated. We used a second-order parametrization of the irradiance spectrum by a single parameter—the F10.7 index—which is a reliable and consistently observed measure of solar activity. The SPAM model consists of two submodels for general and specific use. The first is the Solar-SPAM model of the photon energy flux in the first 190 spectral bands of 1 nm each, which can be used for a wide range of applications in different fields of research. The second model, Aero-SPAM, is designed specifically for aeronomic research and provides a photon flux for 37 specific wavelength intervals (20 wave bands and 16 separate spectral lines within the range of 5–105 nm, and an additional 121.5 nm Ly-alpha line), which play a major role in the photoionization of atmospheric gas particles. We provide the full set of parameterization coefficients that allows for the immediate implementation of the model for research and applications. In addition, we used the Aero-SPAM model to build a ready-to-use numerical application for calculating the photoionization rates of the main atmospheric components N2, O2, O, N and NO with known absorption and ionization cross sections.

Keywords

• solar spectrum
• modeling
• FUV
• EUV
• X-ray
• aeronomy