S. von Alfthan

Multi-GPU simulations of Vlasov's equation using Vlasiator

We present a numerical method, based on a three-dimensional finite volume wave-propagation algorithm, for solving the Vlasov equation in a full six-dimensional (three spatial coordinates, three velocity coordinates) case in length scales comparable to the size of the Earths magnetosphere. The method uses Strang splitting to separate propagation in spatial and velocity coordinates, and is second-order accurate in spatial and velocity spaces and in time. The method has been implemented on general-purpose graphics processing units for faster computations and has been parallelised using the message passing interface.

Ion Acceleration by Flux Transfer Events in the Terrestrial Magnetosheath

We report ion acceleration by flux transfer events in the terrestrial magnetosheath in a global two-dimensional hybrid-Vlasov polar plane simulation of Earth’s solar wind interaction. In the model we find that propagating flux transfer events created in magnetic reconnection at the dayside magnetopause drive fast-mode bow waves in the magnetosheath, which accelerate ions in the shocked solar wind flow. The acceleration at the bow waves is caused by a shock drift-like acceleration process under stationary solar wind and interplanetary magnetic field upstream conditions. Thus, the energization is not externally driven but results from plasma dynamics within the magnetosheath. Energetic proton populations reach the energy of 30 keV, and their velocity distributions resemble time-energy dispersive ion injections observed by the Cluster spacecraft in the magnetosheath.

Hybrid-Vlasov simulations of the Earth's collisionless bow shock and foreshock region

We present magnetospheric simulation results obtained with the hybrid-Vlasov code Vlasiator. In this model, the ion distribution function is propagated in up to three spatial and three velocity dimensions with Vlasovs equation, while electrons are treated as a massless charge-neutralising fluid. Therefore ion kinetic effects are fully included in the description. One major strength of the model is the unprecedented quality of the ion distribution functions due to the uniform sampling and the absence of statistical noise. Another strength lies in the robust finite volume algorithm which yields good numerical stability especially in shock modelling.

Ion distributions in the Earth's foreshock region: Hybrid-Vlasov simulations and spacecraft observations

Summary form only given. We present the ion distribution functions in the terrestrial foreshock, simulated by the hybrid-Vlasov model called Vlasiator and observed by the THEMIS and Cluster spacecraft. In the hybrid-Vlasov description, the ion distribution function is propagated in up to three spatial and three velocity dimensions and electrons are modelled as a massless charge-neutralising fluid. Vlasiator was used to model self-consistently the terrestrial bow shock and foreshock regions in the ecliptic plane (two spatial, three velocity dimensions). The simulations were run for tens of ion gyroperiods over hundreds of ion inertial lengths. Vlasiator provides, for the first time, a large-scale picture of the ion distribution in the foreshock with a quality comparable to or even better than spacecraft data thanks to the uniform velocity space sampling and the absence of statistical noise. This allows us to study the interaction between the backstreaming ions and the solar wind, which can trigger instabilities leading to waves in the foreshock. This poster will feature a simulation snapshot on a large scale including the simulated ion distribution functions at high spatial resolution, as well as comparison to spacecraft data. Beam and ring-beam distributions are present near the foreshock edge. The distributions become progressively more intermediate/cap-shaped with increasing distance from the foreshock edge, including occurrences of multiple-cap distributions. At the same time the drift speed relative to the solar wind decreases deeper in the foreshock. Diffuse distributions are present near the quasi-parallel bow shock.