Kinetic simulations of the Solar Wind Termination Shock

We use a fully kinetic particle-in-cell method to self-consistently simulate the solar wind termination shock with all physical properties available from Voyager 2. We have performed a set of simulations with varying velocity distribution functions for the pickup ions, since it was not determined by Voyagers measurements. The Voyager measurements, according to our simulations, suggest that the pickup ions upstream of the shock are more energetic than generally believed. Specifically, if the PUI velocity distribution function assumes a filled-shell shape in the wind frame, the maximum cutoff speed for the pickup ions should be about 650 km/s to reproduce the Voyager 2 measurements, which is almost twice the local wind speed. We suggest that pickup ions upstream of the shock are energized by adiabatic compression of the solar wind plasma as well as due to an enhanced level of turbulence in a broad foreshock region.