Response of the Martian Thermosphere/Ionosphere to Enhanced Fluxes of Solar Soft X Rays

We have investigated the response of the thermosphere and ionosphere of Mars to enhanced fluxes of solar soft X rays, such as those that have been detected by the SNOE satellite (e.g., Bailey et al., 2000 ). We have constructed standard models by adopting the SC#21REFW and F79050N solar fluxes from H. E. Hinteregger (private communication) (see also Torr et al., 1979 ) for the low and high solar activity models, respectively. We then constructed enhanced soft X-ray models by multiplying the solar photon fluxes for wavelengths below 200 Å by a factor of 3 at low solar activity and by a factor of 6 at high solar activity. We discuss the effects of the larger fluxes of soft X rays on the ion and electron density profiles and the minor neutral density profiles. We find that increasing the Hinteregger soft X-ray fluxes by a uniform factor below 200 Å cannot reproduce the distinct lower peaks that have been observed in some of the electron density profiles measured by the radio science experiment on the Mars Global Surveyor (MGS), and that were modeled previously by Fox et al. (1995) using the SERF2 solar fluxes of Tobiska (1991) . In our model computations, the lower peak appears only as a shoulder, although the magnitude of the electron density at the shoulder is comparable to those exhibited by the MGS radio occultation profiles. This is in contrast to models of the terrestrial ionosphere, where increasing the solar fluxes by a uniform factor of 2–4 for wavelengths less than 250 Å has been found to bring the model electron and NO density profiles, and the shape of the photoelectron flux spectra, into agreement with the measured values