Warm Plasma Population as a Source of the Ring Current

Traditionally the ring current is described by the source population that originates from the plasma-sheet and get energized during periods of enhanced convection accompanying geomagnetic storms or substrom injections. To simulate the build-up of the ring current, plasma source is normally represented by Maxwellian (or Kappa) distribution with some temperature, 5-10 keV at the inner edge of the plasmasheet or 8-10 RE at the equatorial plane. An example is an empirical model of plasma density and temperature by Tsyganenko and Mukai, 2003. Another approach is coupling with a global MHD model, whose plasma parameters (e. g., density and temperature) in the plasma sheet are used as a boundary conditions for the ring current models. As revealed by Van Allen Probes HOPE instrument, ion distributions in the ring current region are non-Maxwellian with warm plasma of a few hundreds of eVs heated perpendicularly at some energies and showing field-aligned distributions at another energies. In addition, the ion distributions and heating are different for different ion species. Recent studies suggest a link between the ring current 'ring' distributions and heating of plasmaspheric plasma, appearing as warm plasma with energies up to 100 eVs. In order to understand how energy is transferred between the ring current, waves and the plasmasphere, we perform simulations with the Comprehensive Inner Magnetosphere-Ionosphere (CIMI) Model. CIMI model calculates the ring current distributions for different species and plasmaspheric density. The simulated distributions are often favorable for EMIC and/or magnetosonic wave generation. Based on the Van Allen Probes data and the calculated wave growth rates, we employ a 'toy model' into CIMI to describe the creation of a warm plasma population. We compare Van Allen Probes data with model results to understand how the warm plasma gets energized and affect the ring current dynamics.