Model Studies of the Structure of the Martian Ionosphere for Various Solar Fluxes in both the EUV and Soft X-ray Regions

A two-peaked structure of the Martian ionosphere has been seen in the Mars Global Surveyor Radio Science electron density profiles. Sometimes the lower peak is seen only as a shoulder and sometimes as a distinct peak. The lower peak is produced by absorption of soft x-rays, and the upper peak by absorption of the main part of the EUV solar fluxes. We present the results of models of the Martian thermosphere/ionosphere in which we employ different solar EUV and soft x-ray fluxes. We have found that a distinct lower peak cannot be reproduced by scaling the solar fluxes below 250 Å by a constant factor of 3--6. This is in contrast to models of the terrestrial low altitude ionosphere, where such a scaling has been found to reproduce the electron density profiles measured by incoherent scatter data (Solomon et al., 2001). We have modeled the ionosphere for solar fluxes from Hinteregger, and the S2K fluxes from K. Tobiska. We find that there is a large difference in the model ionospheres that result from the S2K v1.24 fluxes, which are based on the SNOE soft x-ray data, and the v2.22 fluxes, which are based on the TIMED SEE data. These differences are not limited to the soft x-rays, but extend into the EUV as well. Previous models based on the SERF2 solar fluxes (Tobiska, 1991) had shown the double peaked structure (Fox et al., 1995). We show that the appearance of the double peak depends on both the EUV and soft x-ray fluxes.