The Role of Mesoscale Plasma Sheet Dynamics in Ring Current Formation

Abstract

During geomagnetically active periods ions are transported from the magnetotail into the inner magnetosphere and accelerated to energies of tens to hundreds of keV. These energetic ions, of mixed composition with the most important species being H+ and O+, become the dominant source of plasma pressure in the inner magnetosphere. Ion transport and acceleration can occur at different spatial and temporal scales ranging from global quasi-steady convection to localized impulsive injection events and may depend on the ion gyroradius. In this study we ascertain the relative importance of mesoscale flow structures and the effects of ion non-adiabaticity on the produced ring current. For this we use: global magnetohydrodynamic (MHD) simulations to generate self-consistent electromagnetic fields under typical driving conditions which exhibit bursty bulk flows (BBFs); and injected test particles, initialized to match the plasma moments of the MHD simulation, and subsequently evolved according to the kinetic equations of motion. We show that the BBFs produced by our simulation reproduce thermodynamic and magnetic statistics from in situ measurements and are numerically robust. Mining the simulation data we create a data set, over a billion points, connecting particle transport to characteristics of the MHD flow. From this we show that mesoscale bubbles, localized depleted entropy regions, and particle gradient drifts are critical for ion transport. Finally we show, using identical particle ensembles with varying mass, that O+ non-adiabaticity creates qualitative differences in energization and spatial distribution while H+ non-adiabaticity has non-negligible implications for loss timescales.

Origin of Dawnside Subauroral Polarization Streams During Major Geomagnetic Storms

“…MAGE is a newly developed geospace model that was designed in particular to resolve and study mesoscale structures during storms, such as SAPS (Lin et al., 2021), traveling ionospheric disturbances (Pham et al., 2022), and plasma sheet bursty bulk flows (Sorathia et al., 2021). The MAGE configuration used in the present study couples the Grid Agnostic MHD for Extended Research Applications (GAMERA) global MHD model of the magnetosphere (Sorathia et al., 2020; Zhang, Sorathia, Lyon, Merkin, Garretson, et al., 2019), the Rice Convection Model (RCM) model of the ring current (Toffoletto et al., 2003), Thermosphere Ionosphere Electrodynamics General Circulation Model (TIEGCM) of the upper atmosphere (Richmond et al., 1992), and the RE‐developed Magnetosphere‐Ionosphere Coupler/Solver (REMIX) (Merkin & Lyon, 2010).…”

The Need for a System Science Approach to Global Magnetospheric Models

“…As another example, the GAMERA-REMIX code (Zhang et al, 2019;Sorathia et al, 2020), which combines the GAMERA global MHD solver and the REMIX ionospheric potential solver, runs at ~3,000 core-hours per hour of real time [K. Sorathia, private communication], implying that a simulation study that requires ~200 hourly points could be completed with ~600,000 core-hours. These performance numbers correspond to the high-resolution simulations, e.g., resolving plasma sheet mesoscale dynamics (Sorathia et al, 2021). This is a fairly small allocation on modern high-performance computing architectures.…”

Cross-scale energy cascade powered by magnetospheric convection

“…Dipolarization flows provide an effective mechanism of particle transport and acceleration 15 , 16 . During storms, mesoscale dipolarization flows produce ion and electron injections into the heart of the ring current, which can account for much of its energy density 17 , 18 .…”