An Investigation On The Variations Of Dayside And Nightside Electron Densities Of The Martian Ionosphere

Mars,one of the eight planets of the solar system,has long been the subject of human interest.By studying the ionosphere of Mars,we can further understand the space environment and atmospheric structure of Mars.In this paper,Martian electron density data from Mars Atmosphere and Volatile EvolutioN(MAVEN)satellite are used to investigate the variations of the Martian ionosphere with Solar Zenith Angle(SZA),the influence of strong magnetic field on the electron density of Mars,the day-night difference of Martian electron density and the difference between Martian and Earth's ionosphere.MAVEN's in situ data offer a good chance for us to study Martian ionosphere,especially for Martian nightside ionosphere.MAVEN's data can cover all range of local time(LT)and SZA on Mars with high precision.By analyzing 32 months'electron data from Langmuir Probe Waves(LPW)instrument onboard MAVEN,we found that,the photochemical process is more important than the transport process below 200 km,and the day-night transport can affect the electron density at SZA<110°.For the region above 200 km,the transport process can greatly affect the structure of the topside ionosphere,and the day-night difference of electron densities is much smaller than that below 200 km,and electron density decreases gradually with increasing SZA.During the operation of MAVEN,the periapsis of some orbits can be lower than normal orbits called deep-dips and each of them lasts for about one week.During the deep-dips,MAVEN can detect the condition around the peak electron density altitude.By analyzing the data from MAVEN deep-dip,it was found that strong magnetic field significantly affect the Martian nightside electron density below 200 km.The closed geomagnetic lines might obstruct the electron precipitating process and cause a decrease of electron density.We also analyzed the electron density data from four MAVEN's deep-dips to compare the Martian electron density between day and night as a function of altitude.It was found that the electron precipitating process mainly affects the electron density below 160 km at night.The rapid decrease of nightside electron density above peak altitude can last up to about 160 km,which is about 40 km lower than that in dayside.We also compared Martian electron density data from MAVEN's six deep-dips with the corresponding COSMIC and IRI data of Earth's E layer.Our results demonstrated that the peak electron density of Martian ionosphere is closed to the IRI data from Earth's E layer.The difference of nightside ionosphere between Mars and Earth is slightly greater than that in dayside.