[P-CG18] Planetary Magnetosphere, Ionosphere, and Atmosphere

[PCG18-P11] Simultaneous remote and in-situ observations of ionospheric irregularities at Mars

*Hina Bando¹, Yuki Harada¹, Naoki Terada², Hiromu Nakagawa² (1.Kyoto University, 2.Tohoku University)

Keywords:Mars ionospheric irregularities

It is known that the ionosphere of Mars contains a variety of irregularities. Gurnett et al., [2008] reported that “diffuse echoes”, the traces of which appear unusually diffuse in an ionogram, are sometimes observed by topside ionospheric sounding of Mars Express. These echoes are proposed to be caused by irregularities in the Martian ionosphere. Also, in addition to vertical echoes reflected from the horizontally stratified ionosphere, “oblique echoes” sometimes appear as hyperbola-shaped traces in a radargram. These echoes are typically found in regions where the Martian crustal magnetic field is nearly vertical, and they are interpreted as echoes reflected obliquely from electron density structures deviated from horizontally stratified ionosphere. However, the spatial scale lengths and generation mechanisms of ionospheric irregularities that cause diffuse and oblique echoes are still unknown, partly because comparative studies utilizing remote and in-situ measurements of ionospheric irregularities are yet to be conducted at Mars.

In this study, we surveyed conjunction events in which Mars Express and MAVEN observed the topside ionosphere of Mars at almost the same time and the same location, searching for cases with diffuse echoes or oblique echoes apparent in the Mars Express data. We then investigated variations of the electron, ion,and neutral densities, magnetic fields, and the presence or absence of the hot electron precipitation from MAVEN data. Based on the analysis, it is suggested that the spatial scale lengths of irregularities causing diffuse echo and oblique echoes range from tens to hundreds of kilometers. Additionally, we found an event that exhibits intense diffuse echoes in ionograms, and periodic variations of neutral and ion densities in in-situ data, implying ion-neutral coupling. These observations would provide an important clue as to the unidentified drivers of ionospheric irregularities causing diffuses echoes at Mars.