Substorm Particle Injection into the Ring Current: An MHD with Embedded PIC Simulation Approach

Abstract:

The inner magnetosphere is dynamic, especially during magnetic storms, generating energetic non-thermal particles and strong wave activity. To understand the physics of the ring current region, a multiscale approach using a self-consistent particle-in-cell (PIC) simulation embedded in a global magnetohydrodynamic (MHD) simulation of the solar wind-magnetosphere-ionosphere system called MSPIC is being utilized. This model includes a large fraction of the inner magnetosphere and allows the study of the injection of particles and interaction with plasma waves during magnetic storm related substorms. The calculation begins with electrons and ions propagating earthward from the tail reconnection region. The particle distributions that enter the inner magnetosphere (R < 10 R_E) from the magnetotail already have a suprathermal component which are the seed particles for the ring current. We imposed a steady southward IMF with a magnitude of 8 nT at the upstream simulation boundary of the MHD simulation domain for more than three hours. The solar wind number density was 6 cm^-3, the thermal pressure was 16 pPa, and the velocity was 530 km/s in the X direction toward Earth. After we ran the MHD simulation, we chose an interval to examine during which there were several earthward flow channels and dipolarization fronts. Then, we used the output from this time to populate a large PIC simulation domain in the inner magnetosphere. In GSM coordinates this domain extends over -16 R_E < X < 13 R_E, -13 R_E < Y <13 R_E, -5 R_E < Z < 5 R_E (130 d_i ×116 d_i × 45 d_i where d_i is the ion inertial length). The mass ratio was 256 with realistic ions and more massive electrons. The MSPIC simulation box was loaded by using results from the MHD simulation and ran for 5000 cycles. We found that after 5000 cycles, the current in the inner magnetosphere has increased from that in the MHD calculation. We found that B_z is less than the dipole value in most of the inner magnetosphere because of the effects of external current systems in the MHD simulation. Ions in the ring current drifted from midnight toward dusk but were quickly scattered away.