Calculated electron flux and densities at 10-1000 eV in the dayside Martian ionosphere: comparison with MG S and Viking results

Abstract

The photoelectron flux, ion production rates and electron densities are calculated in the energy range of 10-1000 eV for the dayside Martian ionosphere at solar zenith angle 70o in order to compare electron reflectometer measurements made by Mars Global Surveyor (MGS). These calculations are made by using analytical yield spectrum approach and one-dimensional continuity momentum equations in the presence of horizontal magnetic field where the vertical transport of electrons is inhibited. Using this method, ion and electron densities were also calculated in the absence of horizontal magnetic field at solar zenith angle 45o for all energy ranges. These results are compared with radio occultation measurements made by Viking and other reports which have used one-, two- and three-dimensional models. It is found that the calculated photoelectron flux and density at energy range 10 -1000 eV are in good agreement with the measurements in absence of ionization peaks as observed by electron reflectometer experiment onboard MGS. Above 200 km, the observed horizontal magnetic field of 50 nT is found to be sufficient to explain the electron density measured by electron reflectometer experiment. Below this altitude, there is no effect of horizontal magnetic field in the dayside ionosphere of Mars. The present calculation suggests that X-ray ionization is an important process in the upper ionosphere of Mars at energy greater than 90 eV and the 10-90 eV electron population is controlled by photoionization and photoelectron impact ionizations. The total electron energy population in the dayside ionosphere of Mars is mainly governed by 10-90 eV electron population. The two- and three-dimensional models are not able to reproduce the electron density measured by MGS and Viking. The present one-dimensional model can explain the upper ionosphere of Mars in the presence of precise intensity of magnetic anomaly whose location coincides with the location of electron density measurements.