CONDITIONS IN THE MARTIAN IONOSPHERE ATMOSPHERE FROM A COMPARISON OF A THERMOSPHERIC MODEL WITH RADIO OCCULTATION DATA/

In this paper a possibility to find out some effect of dipole-like int rinsic magnetic field on the plasma scale height at altitudes 180-240 km in the Martian ionosphere, that is above the topside boundary of th e chemically controlled region predicted by existing models of the mag netic field-free ionosphere, is examined. It is assumed that the effec t could be detected if the relationship between plasma and neutral atm osphere scale heights which is expected under the photochemical equili brium conditions in the multicomponent atmosphere remains valid at alt itude region 180-240 km. The plasma scale heights assessed from the da ta collected during the Mariner 9 and Viking 1 sessions are statistica lly analyzed and its trends with the solar zenith angle and F-10.7 flu x are evaluated A half of statistically averaged scale height presente d as a function of the solar zenith angle (SZA) and F-10.7 flux is com pared with the neutral atmosphere scale heights, calculated from the m odel of Izakov and Roste (1996) for the corresponding SZA and F-10.7 f luxes. Since the conditions for the radio occultation experiments duri ng the Mariner 9 and Viking 1 sessions are different a ratio of assess ed plasma scale height to the appropriate neutral atmosphere scale hei ght suits better for comparison than the average scale heights itself does. Employing such ratios the effect of dust content within the lowe r atmosphere on the thermal balance within the topside atmosphere at a ltitude 180-200 km is estimated. (C) 1998 Elsevier Science Ltd. All ri ghts reserved.