Importance of Temperature Anisotropies in the Development of the Storm Time Ring Current

Our 3D multifluid code has been used to model the magnetosphere for substorm and storm conditions and does well predicting substorm onset and storm commencement. It does, however, under predict the intensity of currents in the inner magnetosphere. To resolve this issue, the code has been modified to incorporate temperature anisotropies. Previous studies using single-particle tracking to investigate the energization and injection of ring current ions from ionospheric outflow showed asymmetries between H+ and O+ energization mechanisms and injection into the ring current, as well as the importance of the O+ contribution of the storm time ring current energy density during storm main phase. The current work applies single-particle tracking with time varying fields to calculate changes in the number density, energy density, temperature and temperature anisotropies during the development of storms. The bulk velocities and temperatures of plasma sheet ions are examined in three directions and distribution functions are compared between the single-particle tracking results and an anisotropy model. It is observed that in order for particles to contribute to the development of the storm time ring current, a large perpendicular velocity component is necessary; particles with high parallel velocities are lost. Such results not only suggest the importance of including temperature anisotropies, but also point toward the underlying physical processes driving ring current enhancements.