Preliminary Analysis of Martian Ionospheric Observation data Based on MGS Radio Occultation Experiment

Investigations of planetary atmospheres,ionospheres,rings,and magnetic fields using radio occultation techniques have been conducted by almost every planetary mission and are planned for many future ones.Changes in the frequency,phase,and amplitude of spacecraft radio signal,caused by passage through the atmosphere and ionosphere of the planet,were observed immediately before and after occultation by the planet.According to an inversion method we can get the refractivity,density in the atmosphere near the surface,the scale height in the atmosphere, and the electron density profile of the ionosphere.Over 17 000 radio occultation experiments conducted with MGS since early 1998 have derived two subset data products from the source profiles.Using the data set EDS provided by the MGS Radio Science experiment,we get some figures and tables.As the dayside ionosphere of Mars resembles the Chapman model,we use the least square method to fit the EDS data set,get two parameters c and H_0 in this model.Also the phenomenon of double layers and multilayers of Martian ionosphere is validated and discussed. This phenomenon may reflect the solar wind interaction with the ionosphere under highly variable solar wind dynamic pressure conditions.The change of the peak electron density Nm and peak height Hm relative to longitude,LTST,and SZA in different datasets is discussed.The primary electron density peak is under the local control of photochemical processes.The location of the Martian ionospheric F_1 peak height is determined by how deeply the solar EUV radiation penetrates into the atmosphere.The secondary electron density peak is controlled by soft X-ray ionization,it should be more prominent at high solar activity.The heights of both primary and secondary electron density peaks are regulated by the underlying neutral atmospheric structure. But due to the restriction of spacecraft-earth occultation geometry,only areas in the solar zenith angle of 45°～135°can be detected in this way.In the future Chinese-Russian joint Mars mission, spacecraft-spacecraft occultation will be utilized to detect the dayside and nightside ionosphere, which will greatly complement the global exploration of Martian atmosphere.