Periodicities and Plasma Density Structure of Jupiter's Dawnside Magnetosphere.

Ability to quantify variations in magnetic field topology and density within Jupiter's magnetosphere is an important step in understanding the overall structure and dynamics. The Juno spacecraft has provided a rich data set in the dawnside magnetosphere. The recent Grid Agnostic MHD for Extended Research Applications (GAMERA) global simulation study by Zhang et al. (2021, https://doi.org/10.1126/sciadv.abd1204) showed a highly structured plasmadisc with closed magnetic field lines mapped between the outer dawn‐tail flank and the high‐latitude polar region. To test these model predictions, we examined Juno's magnetic field data and electron/energetic particle data to categorize portions of orbits 1–15 into one of three regions based on plasma confinement: the flux pileup region, the intermediate region, and the plasmadisc region. For each region we examined periodicities from magnetic field fluctuations and particle density fluctuations on the 1–10 hr time scale. Periodicities on this time scale could relate to internal (e.g., plasmadisc structure) or external processes (e.g., Kelvin‐Helmholtz vortices). Similar analysis was performed on the GAMERA simulation with the data split into two regions, an outer (150 > R > 60) region and an inner (R < 60) region. Finally, using published density moments from Huscher et al. (2021, https://doi.org/10.1029/2021JA029446), we compared the relative density variations of the Juno moments and the GAMERA simulation to further understand the overall structure and dynamics of the plasmadisc. The agreement between data and simulation supports the existence of such a highly structured plasmadisc. Plain Language Summary: A very complex and poorly understood problem of Jupiter is the structure and dynamics of the planet's space environment (i.e., "magnetosphere"), due to its sheer size and unique internal ionized gas (i.e., plasma) sourced from the moon, Io. Thanks to the Juno mission, we are able to analyze data from previously unexplored regions around the planet. It has been demonstrated using Voyager data that ionized gas from Io formed a plasma disc‐like structure around the planet in the equatorial plane, becoming less confined in the outer regions. Computer simulations showed a similar structure. In order to investigate this structure, we utilized magnetic field data and particle data from the Juno spacecraft. This data was analyzed to understand the occurrence of regular fluctuations in the magnetic field and gas density, and to understand spatial domains where regular fluctuations occur. Similar analysis was done on magnetic field and density data from simulations for comparison. We found relations between the Juno data and simulation data that suggest a much more variable and structured plasma disc as well as a region in the dawn/tail flank that is magnetically connected to the high latitude polar region. Key Points: Three‐regions with different plasma confinement characteristics have been identified in Jupiter's dawn to postmidnight magnetosphereComparison of Juno data and Grid Agnostic MHD for Extended Research Applications simulations suggest a very structured plasmadiscPeriodicities in 1–4 hr range could be related to plasmadisc structure [ABSTRACT FROM AUTHOR]