Zonal wave structures in the nighttime tropospheric density and temperature and in the D region ionosphere over Mars: modeling and observations

Abstract

We report the first model results of zonal wind perturbations in the nighttime D region ionosphere of Mars during winter and summer seasons at latitude ranges 60°S-64°S and 64.7°N-67.3°N, respectively. The production rate, ion density, and electron density are calculated between longitudes 0° and 360°E due to impact of galactic cosmic rays on the nighttime troposphere of Mars at these latitudes. In this calculation, temperature and air density are used from the measurements made by the radio occultation experiment on board Mars Global Surveyor at low solar activity period. In these seasons the zonal distribution of temperature, air density, and electron density are fitted by a least squares method at altitudes near the surface, 15 km and 30 km. The modes of seasonal winds are also calculated from Fourier analysis at these heights. These measurements suggest mode of wave number 2 in northern high latitudes and wave numbers 3 and 8 in southern high latitudes, respectively. It is found that the nighttime ionosphere of Mars consists of a permanent D peak, which varies with east longitudes in both hemispheres. The modes 2 and 3 of semidiurnal tides dominate the D peak oscillation during the summer and winter seasons, respectively. The water cluster ions H₃O⁺(H₂O)_n, NO₂^-(H₂O)_n and CO₃^-(H₂O)_n are the major species in the D region ionosphere of Mars.