基于无线电掩星观测的火星电离层观测研究进展

Abstract

The early observations of the Mars ionosphere are very limited. Most of the information concerning the ionospheric properties of Mars comes from radio occultation experiments. Recent measurements by Mars Global Surveyor and Mars Express have greatly increased the number of observations of Martian dayside and nightside ionosphere. Large datasets of electron number density profiles have been published online for scientific analysis. Martian ionosphere is influenced by many factors, such as: solar EUV and X ray irradiance, solar wind, solar flare, neutral atmosphere, crustal magnetic field, cosmic rays, meteoric showers and so on. They lead to instantaneous and seasonal variations in Martian ionosphere. In this paper, fundamental principles and features of planetary radio occultation technique are briefly discussed. An introduction of the domestic work concerning the Joint Russia-China Mars exploration (YH-1) is also presented here. New developments in the study of the Martian ionosphere based on radio occultation observations are viewed, mostly from Mars Global Surveyor and Mars Express datasets. The layer structure of Martian dayside ionosphere and factors affecting the variability of each layer are summarized. Here we adopted from Withers, to classify the structure of Martian dayside ionosphere as: M1 below, M1, M2, and M2 above. Some newest findings with regard to the influence of solar activity, neutral atmosphere, crustal magnetic field and meteoric showers on the electron density profile, especially on the peak density and peak height of M2 and M1 layers are presented. This paper also discusses the variation mechanisms and the recent studies of Martian nightside ionosphere. The future research topics of Martian ionosphere will be centered on the interactions of the solar wind and the upper atmosphere, ion loss at Mars, the crustal magnetic control of local ionosphere, structure of night ionosphere and so on.