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withers

HR: 1340h
AN: SA13A-1873 Poster
TI: Numerical Simulations of the Ionosphere of Mars during a Solar Flare
AU: *Lollo, A
EM: alollo@bu.edu
AF: Boston University, Brookline, MA, USA
AU: Withers, P
EM: withers@bu.edu
AF: Boston University, Brookline, MA, USA
AU: Fallows, K
EM: kfallows@bu.edu
AF: Boston University, Brookline, MA, USA
AU: Girazian, Z R
EM: zrjg@bu.edu
AF: Boston University, Brookline, MA, USA
AU: Matta, M M
EM: majdm@bu.edu
AF: Boston University, Brookline, MA, USA
AU: Chamberlin, P C
EM: phillip.c.chamberlin@nasa.gov
AF: NASA Goddard Space Flight Center, Greenbelt, MD, USA
AB: All planetary atmospheres respond to the enhanced flux of extreme ultraviolet (EUV) and x-ray photons emitted from the Sun during a flare. On 15 and 26 April 2001, Mars Global Surveyor observed two solar flares causing up to 200% enhancements in electron densities in the ionosphere of Mars between 80 and 120 km altitude. Here, we attempt to simulate the altitude and peak electron density of the two photochemical layers for both preflare and flare-affected electron density profiles. Our main focus is on the ratio of ion production by electron impact ionization to ion production by photoionization, R. We explore three different types of representation of this ratio: (1) a pressure-dependent parameterization where the ratio asymptotically approaches a high value at high pressure and a low value at low pressure, with a smooth transition region of adjustable vertical extent and pressure level, (2) a wavelength-dependent parameterization derived from the work of Titheridge [1996] of R = 12 exp(-λ/7 nm), (3) a physics-based wavelength-dependent parameterization in which one ion-electron pair is produced by electron impact ionization for every 35 eV by which the energy of an absorbed photon exceeds the ionization potential of carbon dioxide. We find that our results are reasonable using the simplest of these three approaches - one ion-electron pair produced per 35 eV of excess energy. Overall, the simulated electron density profiles are generally consistent with preflare and flare-affected observations from 15 and 26 April 2001. However, simulated flare-affected electron densities below 100 km are substantially smaller than observed. A possible explanation for this lies in the highly dynamic ionization cross section of carbon dioxide at the soft x-ray wavelengths that dominate the attenuated flux at these altitudes.
DE: [5435] PLANETARY SCIENCES: SOLID SURFACE PLANETS / Ionospheres
SC: SPA-Aeronomy (SA)
MN: 2011 Fall Meeting