Multiple Scattering Effects in the Interplanetary Medium: Evaluation Using SOHO SWAN and MAVEN EUVM Lyman α Measurements

Eric Quémerais (1) , Edward Thiemann (2) , Martin Snow (2) , Stéphane Ferron (3) , Walter Schmidt (4)

1 HELIOS - LATMOS
2 LASP - Laboratory for Atmospheric and Space Physics [Boulder]
3 ACRI-ST - Analytic and Computational Research, Inc. - Earth Sciences
4 FMI - Finnish Meteorological Institute

Interplanetary background measurements can be used to derive the solar flux that is illuminating the atoms in the interplanetary medium. We present a new algorithm combining measurements from the SWAN‐SOHO Lyman α photometer with Earth‐based solar flux measurements to derive the solar illuminating flux at Lyman α in any direction along the ecliptic plane. The modulations of the solar flux and the interplanetary background intensity are proportional. The proportionality coefficient is a direct measurement of the fraction of the interplanetary brightness that is due to single scattering in the interplanetary medium. We find that for an observer at 1 AU from the Sun, single scattering photons represent roughly 70% of the total brightness. This new algorithm is tested by a comparison with actual measurements from the EUVM‐MAVEN solar monitor in orbit around Mars since 2014.

Domains: Astrophysics [astro-ph]; Space Physics [physics.space-ph]

Eric Quémerais, Edward Thiemann, Martin Snow, Stéphane Ferron, Walter Schmidt. Multiple Scattering Effects in the Interplanetary Medium: Evaluation Using SOHO SWAN and MAVEN EUVM Lyman α Measurements. Journal of Geophysical Research Space Physics, 2019, 124 (6), pp.3949-3960. ⟨10.1029/2019JA026674⟩. ⟨insu-02151127⟩