基于无线电掩星观测的火星电离层观测研究进展

火星电离层早期的观测数据非常少,除了Viking登陆器对火星电离层的在位测量外,火星电离层的主要物理信息是通过掩星观测方法得到的.近年来,Mars Global Surveyor和Mars Express轨道器通过掩星观测的方法对火星的上层大气和电离层进行了长期的观测,得到了大量的火星电离层电子密度廓线资料.火星电离层受到来自太阳EUV和X射线辐射、太阳风、太阳耀斑、中性大气、表面壳磁场、宇宙射线、流星等多种因素的影响,使其结构发生瞬态或季节性的变化.本文介绍了行星无线电掩星探测的基本原理和技术特点,回顾了国内外科学家们基于已有的火星掩星观测数据（主要是Mars GlobalSurveyor和Mars Express）在火星电离层研究中的一些最新科学成果,并详细介绍了火星电离层的结构和火星夜间电离层的主要特征.

A review on the study of Martian ionosphere based on radio occultation observations

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.