Evidence of Alfvénic Interactions in the Jovian Magnetosphere from the Juno Spacecraft

<p>New insights provided by Juno energetic particle detector measurements indicate signatures of Alfvénic acceleration are more common than previously anticipated. Studies at Earth show that Alfvén waves can substantially accelerate plasma within the magnetosphere. At Jupiter, it is now predicted that Alfvénic acceleration is the dominant mechanism for generating the planet's powerful aurora. This acceleration occurs when the plasma thermal velocity is approximately equal to the Alfvén velocity, which at Jupiter occurs around the plasma sheet boundary. Using Juno JADE and MAG data, we investigate the regions surrounding the plasma sheet boundary layer in order to identify signatures of Alfvénic activity. Our study finds correlations between inertial scale magnetic field perturbations and variations in the local plasma population. We suggest that these signatures may be linked to turbulence in the plasma disk, which could be a source of heating for magnetospheric plasma observed in other studies.</p>

Statistical Properties of Field-Aligned Currents in the Plasma Sheet Boundary Layer

<p>Field-aligned currents (FACs), also known as Birkeland currents, are the agents by which momentum and energy can be transferred to the ionosphere from solar wind and the magnetosphere, exhibiting a seasonal variation as that of ionospheric conductance at low altitude. By using magnetic field and plasma measurements from the Magntospheric Multiscale (MMS), we estimated the properties of the small-scale FACs in the plasma sheet boundary layer (PSBL) region. The occurrence rates of those FACs are larger near the midnight plane and near the flank region; they are also larger in the northern (summer) hemisphere than in the southern hemisphere, especially for the earthward FACs. Different distribution patterns as a function of plasma β are found for the Beam-type FACs and the Flow-type FACs (accompanied with observable perpendicular currents). The latter are closer to central plasma sheet (higher β) and their occurrence rate decreases linearly toward tail lobe (lower β), while the former mainly appear within the β range of 0.1 to 1. FAC magnitudes show little dependence on plasma β, while they would increase when approaching Earth generally. The occurrence rate and magnitude of FACs both increase from low to high geomagnetic activity, consistent with observation at ionospheric altitude. The main carriers for FACs in PSBL are thermal electrons, while cold electrons sometimes could also have contribution, especially under high geomagnetic activity. This study shows that FACs in the PSBL exhibit an asymmetry of occurrence rate between the northern and southern hemisphere and different signatures under low and high geomagnetic activity, which are consistent with FACs at ionospheric altitude. This demonstrates that FACs are significant in magnetosphere-ionosphere coupling and illustrates the possible ionospheric feedback effects to magnetosphere in the nightside.</p>

MMS observations of reconnection separatrix region in the magnetotail at different distances from the active neutral X-line

<p>The region surrounding the reconnection separatrix consists of the multitude of particle and wave transient features (electron, cold and hot ion beams, Hall E&B fields, kinetic Alfven and LH waves, e-holes etc) whose pattern and intensities may vary depending on the stage of reconnection process as well as on the distance from the active neutral line (XNL), whose characterization from observations is not a trivial task. We explore quick MMS entries into the plasma sheet boundary layer from the lobe in 2017 and 2018 tail seasons which potentially could be the crossings of the active separatrix as suggested by energy dispersed beams and polar rain gap features. By combining  the observations of beam dispersion with the measured plasma convection and PSBL motion (obtained using the timing method) we attempt to separate  temporal and spatial (velocity filter) contributions  to the observed beam energy dispersion and evaluate the MMS distance from the XNL. In this report we discuss similarities and differences of separatrix manifestations  observed far from the XNL (at distances exceeding several tens Re) and those found close to it (where the outermost electron beam directed toward the XNL is seen).  One of surprizes was that we were often able to identify the intense Hall-like E&B field structures at very large distances from the XNL.  </p>

MMS/Cluster joint measurements at the vicinity of the plasma sheet boundary layer

<p>On 28th of August 2018 at 5:30 UT, MMS and Cluster were located in the magnetotail at about 16 earth radii (RE). They both suddenly crossed plasma interfaces. Located in the post midnight sector, Cluster transitioned from a cold plasma sheet to a hot plasma sheet whereas MMS, located at 4 RE duskward of Cluster, transitioned from a similar cold plasma sheet to the lobe region via a very short period in a hot plasma sheet. At 05:50 UT MMS returned to a hot plasma sheet and detected a quasi-parallel earthward flow ~ 400 km/s and increased energetic ion and electron fluxes. We use measurements from both missions during this conjunction to describe the possible macroscale evolution of the magnetotail as well as some associated kinetic processes. In particular, we analyze fast and slow non linear electrostatic waves propagating tailward which are detected in the so called electron boundary layer as well as in the hot plasma sheet. We discuss their possible generation mechanisms and link with the large scale evolution of the magnetotail. Finally, we investigate possible effects related to the dawn-dusk asymmetry of the magnetotail.</p>