Diffuse electron precipitation in magnetosphere-ionosphere-thermosphere coupling

Auroral precipitation plays an important role in magnetosphere-ionosphere-thermosphere (MIT) coupling by enhancing ionospheric ionization and conductivity at high latitudes. Diffuse electron precipitation refers to scattered electrons from the plasma sheet that are lost in the ionosphere. Diffuse precipitation makes the largest contribution to the total precipitation energy flux and is expected to have substantial impacts on the ionospheric conductance and affect the electrodynamic coupling between the magnetosphere and ionosphere-thermosphere. Kinetic theory and observational analysis also demonstrate that diffuse precipitation is subject to multiple reflection effects, i.e. secondary electrons produced by the primary precipitation are reflected between the north and south hemispheres multiple times before they are fully lost in the atmosphere. In this study, we make use of the newly developed Multiscale Atmosphere-Geospace Environment (MAGE) model developed at the NASA DRIVE Science Center for Geospace Storms (CGS) to explore the role of diffuse electron precipitation in MIT coupling. Diffuse precipitation in MAGE is derived from the electron distribution in the Rice Convection Model (RCM), a ring current model that solves for energy dependent drifts of electrons and ions. Diffuse precipitation, together with mono-energetic electron precipitation based on parameterization of the magnetohydrodynamic (MHD) parameters from the Grid Agnostic MHD with Extended Research Applications (GAMERA) magnetosphere model, are input to the Thermosphere Ionosphere Electrodynamic General Circulation Model (TIEGCM) to calculate the ionospheric ionization rate and conductivity and height-integrated conductance. With controlled numerical experiments, we investigate 1. how the diffuse precipitation affects the location and structure of a mesoscale ionospheric convection process, i.e., subauroral polarization streams (SAPS); 2. How multiple reflection effects impact the ionosphere-thermosphere and their coupling with the magnetosphere. Our study demonstrates that diffuse electron precipitation plays a critical role in determining the location and structure of SAPS. The multiple reflection effects make diffuse precipitation number flux and energy flux a few times higher than the unmodified precipitation, resulting in a greatly enhanced auroral ionospheric conductance, lower cross polar cap potential,  higher total field-aligned currents, and changes in global thermospheric winds and temperature. Therefore, diffuse electron precipitation has both local and global impacts on MIT coupling.