Application of Viking radio occultation data to the future studies of the Martian ionosphere

Topside electron density profiles provide information on the solar wind interactions with the terrestrial planets, Venus and Mars. At Mars we have a picture of the topside only from two Viking Lander profiles and from radio occultation measurements. These produced somewhat ambiguous results, and so the existence of a Martian "ionopause" and of the Martian magnetic field is much-debated. Topside ionospheric sounding is a potentially powerful technique for remotely sensing global upper ionosphere structure. The Mars-96 Long Wave Radar will finally provide the opportunity to use this capability. Using examples of electron density profiles obtained by radio occultation of Vikings we illsutrate the potential of the radar technique for determining such profiles, and by implication for identifying such features as ionopauses and the magnetic field in the Martian ionosphere. (C) 1998 COSPAR. Published by Elsevier Science Ltd.