Study of magnetosphere dynamics combing geospace and planetary missions

Solar system missions studying the sun and the planets in the inner and outer heliosphere use gravity assists of the planets to reach the target orbit of the missions. If such a maneuver happens around Earth, these observations enable us a unique multipoint observation of the magnetosphere together with other existing geospace missions as was the case of the Bepicolombo in April 2020 and the Solar Orbiter in November 2021 and is expected for JUICE in August 2024. Although the spacecraft during flybys are usually not operated in a full science mode, a new constellation with other fleet of spacecraft in Geospace can provide important information in particular for studying large-scale magnetospheric dynamics. In this presentation we discuss the three-dimensional evolution of the magnetotail current of a substorm on April 10, 2020 that took place during the Earth-flyby interval of Bepicolombo. Magnetotail disturbances are observed by GOES 17 and Cluster in the midnight region, while BepiColombo spacecraft traversed the premidnight region duskward at 9-11 RE downtail. The four Cluster satellites, which were separated mainly in north-south direction, crossed the inner magnetosphere successively from north to south. They enable us to monitor the vertical (latitudinal) structure and the sequential changes of the magnetotail current sheet until the end of the recovery phase of the substorm. Multiple dipolarizations and multiple transient field-aligned currents (FAC) were observed by Cluster. Using the unique dataset from these multi-point observations, we examine the structure of the large-scale current sheet and analyze the embedded transient intense field-aligned current disturbances. By also comparing the observations with an empirical magnetic field model, we obtain the changes of the near-Earth magnetotail structure during the multiple dipolarization event.