Recent advances on magnetic reconnection and dipolarization at Saturn

<p>Magnetic reconnection and dipolarization are crucial processes in driving magnetospheric dynamics, including particle energization, mass circulation, auroral processes etc. Recent studies revealed that these processes at Saturn are fundamentally different to the ones at Earth. The reconnection and dipolarization processes are far more important than previously expected at Saturn’s dayside magnetodisc. Dayside magnetodisc reconnection was directly identified using Cassini measurements (Guo et al. 2018), and was found to be drizzle-like and rotating in Saturn’s magnetosphere (Yao et al. 2017 and Guo et al. 2019). Moreover, magnetic dipolarization could also exist at Saturn’s dayside, which is fundamentally different to the terrestrial situation (Yao et al. 2018). We here review these recent advances and their potential implications to future investigations, for example the application to Jupiter’s magnetosphere.</p>

On the role of neutral flow in field-aligned currents

In this brief note we explore the role of the neutral atmosphere in magnetosphere–ionosphere coupling. We analyze momentum balance in the ion rest frame to form hypotheses regarding the role of neutral momentum in the lower ionosphere during geomagnetic storms. Neutral momentum that appears in the ion rest frame is likely the result of momentum imparted to ionospheric ions by solar wind flow and the resultant magnetospheric dynamics. The resulting ion-neutral collisions lead to the existence of an electric field. Horizontal electron flow balances the momentum supplied by this electric field. We suggest a possible role played by the neutral atmosphere in generating field-aligned currents due to local auroral heating. Our physical interpretation suggests that thermospheric neutral dynamics plays a complementary role to the high-latitude field-aligned currents and electric fields resulting from magnetospheric dynamics. Keywords. Ionosphere (ionosphere–magnetosphere interactions; polar ionosphere) – magnetospheric physics (magnetosphere–ionosphere interactions)