Global simulation of proton precipitation due to field line curvature during substorms

The low latitude boundary of the proton aurora (known as the Isotropy Boundary or IB) marks an important boundary between empty and full downgoing loss cones. There is significant evidence that the IB maps to a region in the magnetosphere where the ion gyroradius becomes comparable to the local field line curvature. However, the location of the IB in the magnetosphere remains in question. In this paper, we show simulated proton precipitation derived from the Field Line Curvature (FLC) model of proton scattering and a global magnetohydrodynamic simulation during two substorms. The simulated proton precipitation drifts equatorward during the growth phase, intensifies at onset and reproduces the azimuthal splitting published in previous studies. In the simulation, the pre‐onset IB maps to 7–8 R E for the substorms presented and the azimuthal splitting is caused by the development of the substorm current wedge. The simulation also demonstrates that the central plasma sheet temperature can significantly influence when and where the azimuthal splitting takes place. Key Points Using a simple model, proton aurora can be simulated using a global MHD model The simulation shows azimuthal splitting of the proton aurora The azimuthal splitting is related to the growth of the substorm current wedge