D, E, and F layers in the daytime at high-latitude terminator ionosphere of Mars: comparison with Earth's ionosphere using COSMIC data

Abstract

We report the first model result for ion production rates and densities of positive ions, negative ions, and electrons in the dayside Martian ionosphere from 0 to 220 km. These calculations are made at solar zenith angle 77° for low solar activity periods. The calculated electron density is compared with the radio occultation measurements made by Mars Global Surveyor (MGS) and Mars 4/5 on Mars and by Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) on Earth. Our calculation suggests that the daytime ionosphere of Mars can be divided into D, E, and F layers at altitude ranges ~25-35 km, ~100-112 km, and ~125-145 km with the concentrations 7 × 101 cm^-3, 2.4 × 10⁴ cm^-3, and 8.4 × 10⁴ cm^-3 owing to the impact of galactic cosmic rays, X rays (10-90 Å), and solar EUV (90-1026 Å) radiations, respectively. The water cluster ions H₃O⁺(H₂O)_n, NO₂ -(H₂O)_n, and CO₃ -(H₂O)_n are dominated in the D region, while NO⁺, CO₂⁺, and O₂⁺ are major ions in the E and F regions. The calculated E and F peak heights are in good agreement with MGS observation. The value of D peak density is lowered by 1 and 2 orders of magnitude from the measurements on Mars and Earth, respectively. The height of F layer peak is lower by factor of 1.8 in the Martian ionosphere as compared to that observed in the ionosphere of Earth. E regions are created at nearly the same heights in the ionospheres of both planets, but the layer thickness is considerably less on Mars than on Earth. This implies that solar EUV energy is deposited within smaller-altitude range in the upper ionosphere of Mars as compared to the corresponding altitude range in the upper ionosphere of Earth.