FISM-P: A Solar EUV and FUV Irradiance Model Optimized for Planetary Aeronomy

Solar Extreme Ultraviolet (EUV, ~10-121 nm) and Far Ultraviolet (FUV, ~122-200 nm) radiation is a primary energy input to the tenuous atmospheric regions of most planets and their satellites. EUV and FUV radiation ionizes and dissociates gases in these regions, heating the constituent neutral and charged species, changing atmospheric composition and creating an ionosphere. Solar irradiance measurements and models for Earth are not directly applicable to other planets since solar UV radiation is not emitted isotropically into the solar system, and is instead highly variable in both space and time.

The Flare Irradiance Spectral Model for Planets (FISM-P) estimates solar irradiance from 0-195 nm for planetary bodies throughout the solar system from 1967 through the present. FISM-P is an iteration of FISM, an empirical model originally developed for upper atmospheric studies at Earth. It uses a series of optimal space- and ground-based solar measurements, decomposed into components of the major timescales of solar variability (e.g. solar rotation, solar cycle), which are related to spectral irradiance measurements through a series of regression coefficients. FISM-P incorporates recent improvements for the extrapolation Earth based measurements to other locations in the solar system enabled by the MAVEN mission, which includes the EUV Monitor (EUVM), an instrument that measures calibrated EUV irradiance at Mars. The availability of calibrated irradiance measurements elsewhere in the solar system allows for a direct validation of methods used to improve estimates of irradiance at other planets and a quantification of the associated error. In this presentation, we present the methods used by FISM-P to estimate irradiances at other planets, and the resulting spectra and associated uncertainty.