Speaker
Description
Solar extreme ultraviolet (EUV) and X-ray photons are a primary source of energy for the upper atmospheres of terrestrial planets. Soft X-ray (SXR, 0-10 nm) irradiance is quite variable, particularly during solar flare events, and is difficult to extrapolate to other planets based on Earth observations alone. Meanwhile, photoelectrons are a product of solar EUV and SXR irradiance photoionizing the neutral atmosphere, whose energy-flux distributions preserve distinctive features of the incident solar EUV spectra. Particularly, oxygen Auger photoelectrons are produced by solar SXR photons at wavelengths shorter than ~2.5 nm. This study uses a novel approach to infer the SXR irradiance from Auger photoelectron fluxes. More specifically, we derive the fit function between the oxygen Auger photoelectron fluxes observed by the Mars Global Surveyor spacecraft and solar irradiance at 0.1-0.8 nm observed by Geostationary Operational Environmental Satellite (GOES) X-ray Sensors (XRS) for selected solar flare events. The fit function is then applied to all the Auger photoelectron observations by MGS to derive the 0.1-0.8-nm SXR irradiance from 1999 to 2006. Using the same database, 167 solar flare events ranging from C-Class to X-Class are identified at an additional vantage point away from Earth. This catalog of flares observed at Mars is of particular interest for studying over-the-limb and far-side flare effects on near-side disk radiance and radiative transport in the solar corona, which improves our understanding of the solar flare generation and better quantifies solar EUV/SXR fluxes.
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