P21A-2050
New Sub-nanometer Spectral Estimates of the 0-5 nm Solar Soft X-Ray Irradiance at Mars Using the Extreme UltraViolet Monitor (EUVM) Onboard MAVEN

Tuesday, 15 December 2015
Poster Hall (Moscone South)
Edward Thiemann1, Francis Gerard Eparvier2, Phillip C Chamberlin3, Thomas N Woods4, William K Peterson2, David L Mitchell5, Shaosui Xu6 and Michael Warren Liemohn6, (1)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (2)University of Colorado at Boulder, Boulder, CO, United States, (3)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (4)Univ Colorado, Boulder, CO, United States, (5)University of California Berkeley, Berkeley, CA, United States, (6)University of Michigan Ann Arbor, Ann Arbor, MI, United States
Abstract:
The Extreme UltraViolet Monitor (EUVM) onboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) probe at Mars characterizes the solar extreme ultraviolet (EUV) and soft x-ray (SXR) input into the Martian atmosphere. EUVM measures solar irradiance at 0-7 nm, 17-22 nm and 121.6 nm at a nominal 1 second cadence. These bands were selected to capture variability originating at different heights in the solar atmosphere; and are used to drive the Flare Irradiance Solar Model at Mars (FISM-M) that is a model of the solar spectrum from 0.1-190 nm with 1 nm resolution and produced routinely as the EUVM Level 3 data product.

The 0-5 nm range of the solar spectrum is of particular aeronomic interest because the primary species of the Mars upper atmosphere have Auger transitions in this range. When an Auger transition is excited by incident SXR radiation, secondary electrons are emitted with sufficient energy to further ionize the atmosphere. Because these transitions are highly structured, sub-nm resolution of the solar spectrum is needed in the 0-5 nm range to fully constrain the solar input and more accurately characterize the energetics of the upper atmosphere.

At Earth, .1 nm resolution estimates of the solar 0-5 nm range are produced by the X-ray Photometer System (XPS) onboard the SOlar Radiation and Climate Experiment (SORCE) satellite by combining broad-band SXR measurements with solar flare temperature measurements to drive an atomic physics based forward model of solar coronal emissions. This spectrum has been validated with other models as well as with photo-electron and day glow measurements at Earth.

Similar to XPS, the EUVM 0-7 nm and 17-22 nm bands can be used to produce an XPS-like model at Mars, but with reduced precision due to differences in the available bands. We present first results of this technique applied to a set of solar flares observed by MAVEN EUVM and Earth assets. In addition to comparing EUVM and Earth-asset derived 0-5 nm solar spectra to characterize the effectiveness of this technique, we compare Mars atmospheric photoelectron spectral measurements made by MAVEN's Solar Wind Electron Analyzer (SWEA) against modeled photoelectron spectra which use the EUVM derived 0-5 nm solar spectrum as an input.

<< Previous Abstract | Next Abstract >>