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.

Solar wind charge exchange (SWCX) generated soft X-rays are used extensively to study the interfaces between charged and neutral particles throughout the solar system. This paper outlines the development of a model of Jupiter’s magnetosheath using MHD derived boundary equations and a combination of in situ Juno measurements and numerical models for neutral and charged particle distributions. These are then used to model SWCX emissions in the Jovian magnetosheath for the O$_{VII}$ triplet to determine if the magnetosheath could be imaged in a similar fashion to the planned SMILE mission at Earth. We determine that whole detector counts per minute range from 10$^{-5\pm1}$ to 10$^{-3\pm1}$ for various spacecraft, and, as such, argue that with current instrument sensitivity it is infeasible to study the X-ray emissions from the Jovian magnetosheath. However, with a theoretical x-ray imager with an effective area of 1m$^2$ and FOV of $120^{\circ}\times120^{\circ}$ increases to a peak of $\sim$10$^{0\pm1}$ c/min when observing from a distance of 40 R$_J$. We also discuss the implications of the low emission rates on other higher signal X-ray observations at Jupiter and the possibility of Saturn being a better target for such a mission.

A document by Junjie Chen. Click on the document to view its contents.

The magnetosphere, ionosphere and thermosphere (MIT) act as a coherently integrated system (geospace), driven in part by solar influences and characterized by variability and complexity. Among the most important and yet uncertain aspects of the geospace system is energy and momentum coupling between regions, which is, in part, accomplished by the transfer of charged particles from the magnetosphere to the ionosphere in a process known as particle precipitation, and in the opposite direction by ion outflow. Both processes are inherently multiscale and manifest the variabilities and complexities of the geospace system. Despite the importance of the transfer of particles, existing models are increasingly ill-equipped to provide the specification necessary for the growing demand for geospace now- and forecasts. Due to recent trends in the availability of data, we now face an exciting opportunity to progress particle transfer in geospace through the intersection of traditional approaches and state-of-the-art data-driven sciences. We reveal novel particle transfer models utilizing machine learning (ML), present results from the models, and provide an evaluation of their capabilities including comparisons with observations and the current ’state-of-the-art’ models (e.g., OVATION Prime for particle precipitation and the Gamera-Ionosphere Polar Wind Model for ion outflow). We detail the data wrangling required to utilize the available geospace observations to make progress on the long-standing challenge of particle transfer and place specific emphasis on the discovery possible when ML models are appropriate and robustly interrogated in the context of physical understanding. Our presentation helps illustrate the trends in the application of data science in space science.

Thermospheric mass density perturbations are commonly observed during geomagnetic storms. The sources of these perturbations have not been well understood. In this study, we investigated the thermospheric density perturbations observed by the CHAMP and GRACE satellites during the 24-25 August 2005 geomagnetic storm. The observations show that large neutral density enhancements occurred not only at high latitudes, but also globally. In particular, large density perturbations were seen in the equatorial regions away from the high-latitude, magnetospheric energy sources. We used the high-resolution Multiscale Atmosphere Geospace Environment (MAGE) model to reproduce the consecutive neutral density changes observed by the satellites during the storm. The MAGE simulation, which resolved mesoscale high-latitude convection electric fields and field-aligned currents, and included a physics-based specification of the auroral precipitation, was contrasted with a standalone ionosphere-thermosphere simulation driven by an empirical model of the high-latitude electrodynamics. The comparison demonstrates that a first-principles representation of highly dynamic and localized Joule heating events in a fully coupled whole geospace model such as MAGE is critical to accurately capturing both the generation and propagation of traveling atmospheric disturbances (TADs) that produce neutral density perturbations globally. In particular, the MAGE simulation shows that the larger density peaks in the equatorial region that are observed by CHAMP and GRACE are the results of TADs, generated at high latitudes in both hemispheres, propagating to and interfering at lower latitudes. This study reveals the importance of investigating thermospheric density variations in a fully coupled geospace model with sufficiently high resolving power.

We have taken a key step in evaluating the importance of ionospheric outflows relative to electrodynamic coupling in the thermosphere’s impact on geospace dynamics. We isolated the thermosphere’s material influence and suppressed electrodynamic feedback in whole geospace simulations by imposing a time-constant ionospheric conductance in the ionospheric Ohm’s law in a coupled model that combines the multi-fluid Lyon-Fedder-Mobarry magnetosphere model with the Thermosphere Ionosphere Electrodynamic General Circulation Model and the Ionosphere Polar Wind Model that includes both polar wind and transversely accelerated ion species. Numerical experiments were conducted for different thermospheric states parameterized by F10.7 for interplanetary driving representative of the stream interaction region that swept past Earth on 27 March 2003. We demonstrate that thermosphere through its regulation of ionospheric outflows influences magnetosphere-ionosphere (MI) convection and the ion composition, symmetries, x-line perimeter and magnetic merging of the magnetosphere. Feedback to the ionosphere-thermosphere from evolving MI convection, and Alfvénic Poynting fluxes and soft (~ few 100 eV) electron precipitation originating in the magnetosphere, in turn, modify the evolving O+ outflow properties. The simulation results identify a variety of observed magnetospheric features that are attributable directly to the thermosphere’s material influence: Asymmetries in O+ outflow fluxes and velocities in the pre/postnoon low-altitude magnetosphere, dawn/duskside lobes and pre/postmidnight plasmasheet; O+ distribution of the plasmasheet; magnetic x-line location and reconnection rate along it. O+ outflows during solar maximum conditions (high F10.7) tend to counteract the plasmasheet’s pre/postmidnight asymmetries caused by the night-to-day gradient in ionospheric Hall conductance.

Plasmoid is a key process for transferring magnetic flux and plasma in planetary magnetospheres. At Earth，plasmoid is a key media transferring energy and mass in the “Dungey Cycle” magnetospheric circulation. For giant planets, plasmoid is primarily generated by the dynamic processes associated with “Vasyliunas Cycle”. It is generally believed that planetary magnetotails are favourable for producing plasmoids. Nevertheless, recent study reveals that magnetic field lines could be sufficiently stretched to allow magnetic reconnection (Guo et al. 2018a) in Saturn’s dayside magnetodisc. And in the study, we report direct observations of plasmoid in Saturn’s dayside magnetodisc. Moreover, we perform a statistical investigation on the global plasmoid electron density distribution. The results show an inverse correlation between the nightside plasmoid electron density and local time, and the maximum plasmoid electron density around prenoon local time on the dayside. These results are consistent with the magnetospheric circulation picture associated with“Vasyliunas Cycle”.