A possible intrinsic mechanism for the quasi-periodic dynamics of the Jovian magnetosphere

摘要

Most regions of the Jovian magnetosphere covered by the Galileo spacecraft measurements undergo quasi-periodic modulations with a time period of several Earth days. These modulations appear in various field and particle properties. Most prominent are periodically recurring ion flow bursts associated with disturbances in the meridional component of the magnetic field in the Jovian magnetotail or variations of the energy spectral shape of the particle distribution associated with the stretching and dipolarization of the magnetic field. Each individual cycle of these modulations is believed to represent a global reconfiguration of the Jovian magnetosphere. We present a simple conceptual model for these periodic processes assuming (1) ion mass loading from internal plasma sources and (2) fast planetary rotation causing magnetotail field line stretching due to centrifugal forces. This leads to a magnetotail configuration favoring magnetic reconnection. Magnetic reconnection causes plasmoid formation and release as well as dipolarization of field lines connected to the planet. Continued mass loading leads again to a stretching of the tail field lines. Our model shows that the suggested intrinsic mechanism can explain the observed periodicities of several days in Jovian substorm-like processes.