Banana Current in the Inner Magnetosphere Observed by Van Allen Probes

By using the magnetic field data from Van Allen Probes, we analyzed the distribution characteristics of the electromagnetic environment in the inner magnetosphere on different Dst* index and magnetic local time. Our results show that for the response of different current systems, the dawn-dusk and noon-midnight asymmetry distribution of the residual magnetic field δB increases with Dst* index. When Dst* < −60 nT, a “banana”-shaped geomagnetic field negative disturbance peak region appears in the sector from midnight to dusk. Then, we obtained the azimuthal current density and found the asymmetric internal eastward and external westward ring current. Through the vector analysis of three-dimensional current density, the current density vector distribution in the magnetic equatorial plane is completely displayed for the first time, which directly proves the existence of banana current near r = 3.0–4.0 R_E during strong geomagnetic storms.