Simulation of the westward traveling surge and Pi 2 pulsations during substorms

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Abstract
The westward traveling surge and the Pi 2 pulsations are simulated as a consequence of an enhanced magnetospheric convection in a model of magnetosphere‐ionosphere coupling. The coupling is characterized by the bouncing of Alfvén waves launched by the enhanced convection. The reflection of Alfvén waves from the ionosphere is treated in which the height‐integrated conductivity is allowed to be highly nonuniform and fully anisotropic. The reflection of Alfvén waves from the magnetosphere is characterized by the coefficient Rm, depending on whether the field lines are open or closed. On open field lines the reflection coefficient from the magnetopause is given by Rm ≃ −1. On closed field lines the reflection coefficient is given by (1) Rm ≃ +1 in the near‐earth plasma sheet and (2) −1 ≲ Rm ≲ +1 in the low‐latitude boundary layer and the distant plasma sheet. The conductivity in the model is self‐consistently enhanced with increasing upward field‐aligned current density. The results of the simulation, including the convection pattern, the electrojets, the field‐aligned current, the conductivity enhancement, the oscillation of the westward electrojet, and the average speed of the westward surge are in reasonable agreement with the features of the westward traveling surge and the Pi 2 pulsations observed during substorms.