The MAVEN EUVM model of solar spectral irradiance variability at Mars: Algorithms and results

Solar extreme ultraviolet (EUV) radiation is a primary energy input to the Mars atmosphere, causing ionization and driving photochemical processes above approximately 100km. Because solar EUV radiation varies with wavelength and time, measurements must be spectrally resolved to accurately quantify its impact on the Mars atmosphere. The Mars Atmosphere and Volatile EvolutioN (MAVEN) EUV Monitor (EUVM) measures solar EUV irradiance incident on the Mars atmosphere in three bands. These three bands drive a spectral irradiance variability model called the Flare Irradiance Spectral Model (FISM)-Mars (FISM-M) which is an iteration of the FISM model by Chamberlin et al. (2007, 2008) for spectral irradiance at Earth. In this paper, we report the algorithms used to derive FISM-M and its associated uncertainties, focusing on differences from the original FISM. FISM-M spectrally resolves the solar EUV irradiance at Mars from 0.5 to 189.5nm at 1min cadence, and 0.1nm resolution in the 6-106nm range or 1nm resolution otherwise. FISM-M is suitable for both daily average and flaring spectral irradiance estimates and is based on the linear association of the broadband EUVM measurements with spectral irradiance measurements, including recent high time cadence 0.1nm resolution measurements from the EUV Variability Experiment (EVE) on the Space Dynamics Observatory (SDO) between 6 and 106nm. In addition, we present examples of model outputs for EUV irradiance variability due to solar flares, solar rotations, Mars orbit eccentricity, and the solar cycle, between October 2015 and November 2016.