Dayside Magnetodisk Reconnection in Jovian System: Galileo and Voyager Observation.

Magnetic reconnection, an essential mechanism in plasma physics that changes magnetic topology and energizes charged particles, plays a vital role in the dynamic processes of the Jovian magnetosphere. The traditional Vasyliūnas cycle only considers the effect of magnetic reconnection at the nightside magnetodisk. Recently, magnetic reconnection has been identified at the dayside magnetodisk in Saturn's magnetosphere and can impact dayside auroral processes. In this study, we provide the first evidence that the dayside magnetodisk reconnection can also occur at Jupiter. Using data from the Galileo and Voyager 2 spacecraft, we have identified 18 dayside reconnection events with radial distances in the range of 30–60 Jupiter radii (RJ). We analyzed the particle (electron and ion) flux, energy spectra, and characteristic energy of these dayside events and compared them to the nightside events. The statistical results show that the energy spectra and characteristic energy of electrons/ions in dayside and nightside magnetic reconnection events are comparable. On average, the characteristic energy of ions on the dayside is higher than that on the nightside. Based on the limited data set, we speculate that the occurrence rate of dayside magnetodisk reconnection should be significant. The dayside Jovian magnetodisk reconnection seems to have a comparable effect on providing energetic particles as that at nightside and to be one of the key processes driving dynamics within the Jovian magnetosphere. Plain Language Summary: Jupiter has the strongest magnetic field among the planets in our solar system. Particles in the space around Jupiter are affected by its magnetic field. Changes in the strength and structure of the local magnetic field, known as magnetic reconnection, cause those particles to undergo rapid acceleration leading to their energization. In the past, magnetic reconnection was thought to be difficult to occur on Jupiter's dayside magnetodisk. In contrast, the recent observation of reconnection at Saturn's dayside magnetodisk strongly implied the possibility of a similar process at Jupiter. In this paper, taking advantage of the archived data from the Galileo and Voyager 2 spacecraft, we provide the first evidence that the dayside magnetodisk reconnection can occur at Jupiter and have an important effect on the energization of particles. Key Points: Dayside magnetodisk reconnection events at 30–60 RJ are identified in the Jovian magnetosphere for the first time18 dayside events are analyzed to compare with nightside events regarding particle flux, energy spectra, and characteristic energyMagnetodisk reconnection at the dayside is as effective as that at the nightside in providing energetic particles to the magnetosphere [ABSTRACT FROM AUTHOR]