Tracing magnetic separators and their dependence on IMF clock

A new, efficient, and highly accurate method for tracing magnetic separators in global magnetospheric simulations with arbitrary clock angle is presented. The technique is to begin at a magnetic null and iteratively march along the separator by finding where four magnetic topologies meet on a spherical surface. The technique is verified using exact solutions for separators resulting from an analytic magnetic field model that superposes dipolar and uniform magnetic fields. Global resistive magnetohydrodynamic simulations are performed using the three-dimensional BATS-R-US code with a uniform resistivity, in eight distinct simulations with interplanetary magnetic field (IMF) clock angles rang-ing from 0 (parallel) to 180 degrees (anti-parallel). Magnetic nulls and separators are found in the simulations, and it is shown that separators traced here are accurate for any clock angle, unlike the last closed field line on the sun-Earth line that fails for southward IMF. Trends in magnetic null locations and the structure of magnetic separators as a func-tion of clock angle are presented and compared with those from the analytic field model. There are many qualitative similarities between the two models, but quantitative dif-ferences are also noted. Dependence on solar wind density is briefly investigated. 1