Consistency check of a global MHD simulation using the test-kinetic approach

The test-kinetic approach is used to study first order particle kinetic effects in the vicinity of the Earth bow shock, and check consistency with a solution obtained in the MHD approximation. The method, also referred to as reverse particle tracing, consists of integrating particle trajectories backward in time, using electromagnetic fields as obtained from an MHD simulation model. By following particles back to a region where the plasma distribution function is known, and using Liouville's theorem, it is possible to compute the distribution function at arbitrary points in space. Compared with the more familiar test-particle approach, where large numbers of particles are followed forward in time, the present method has the advantage of producing distribution functions without statistical errors. The test-kinetic method is applied here in combination with magnetospheric fields obtained with the global MHD code BATS-R-US. Consistency between the MHD solution and the first order kinetic solution is checked by comparing moments of the computed ion distribution function directly with corresponding physical parameters obtained in the MHD approximation. From there, the validity and limitations of both the MHD solution and the inferred particle kinetic solution can be assessed.