Modeling of cusp ion structures during southward and northward IMF with particle tracing code

Cusp ion structures have been used to infer the location and properties of reconnection at the Earth's magnetopause. However, satellite movement relative to reconnection sites creates a temporal/spatial ambiguity in the observations, and empirical models have difficulty to account for the constantly changing magnetospheric phenomena. In this study, we model the cusp ion structures during southward and northward IMF by using a particle tracing code with electromagnetic fields obtained from the OpenGGCM global magnetosphere-ionosphere model. Integrating Lorentz equations by using the 4th order Runge-Kutta method, the code traces particles backward in time from given locations along a satellite trajectory to source regions where the particle phase space densities are known, such as magnetosphere or magnetosheath. We then calculate the phase-space density based on information from the source regions using Liouville's theorem. The resulting energy-time spectrograms of the distribution functions can be directly compared with observations. We first show analytical results for an ideal rotational discontinuity as a test case, and then present results for specific events with southward and northward IMF.