Magnetospheric Response to a Pressure Pulse in a Three‐Dimensional Hybrid‐Vlasov Simulation

Vlasiator is a high‐performance ion‐kinetic code that is now conducting 3D hybrid‐Vlasov simulations of the global magnetosphere. We use Vlasiator to investigate the impact of a pressure pulse with southward‐oriented magnetic field on the Earth's magnetosphere. The simulation driving parameters are comparable to conditions that have led to geomagnetic storms. Our pressure pulse simulation reproduces many physical effects, namely the expansion of the auroral oval, the development of field‐aligned currents, enhanced particle precipitation near the open/closed field line boundary, and compression of Earth's magnetopause. This demonstrates the effectiveness of the hybrid‐Vlasov approach for moderate driving conditions. Our investigation of the time‐dependent magnetopause compression motivates a generalization of the existing theory. Specifically, we find that accounting for the finite transition time of the solar wind dynamic pressure improves the model's description of the magnetopause oscillations. Plain Language Summary We perform state‐of‐the‐art simulations of the interaction of near‐Earth space environment with the incoming material ejected from the Sun. The response of Earth's magnetic field to such ejecta is known as a “geomagnetic storm.” Our simulation approach captures the motion of protons more accurately than commonly used fluid models, but at the cost of making the simulations more computationally intensive. To validate this novel approach, we compare the output of our simulation with established observational signatures of the initial storm phase. We find that our simulation, of relatively moderate storm conditions, reproduces known effects that are relevant to society. Such effects include particle precipitation into the atmosphere and reconfiguration of global magnetic field. Our simulation does diverge from established models on how the magnetopause, the boundary between Earth's magnetic environment and the solar wind, moves in response to a sudden increase of incoming pressure. This inspires a modification of the theory of magnetopause motion, which better accounts for the detailed time profile of the incoming solar wind. Key Points Vlasiator's 3D hybrid‐kinetic model of the global magnetosphere produces expected behavior for a pressure pulse arriving at Earth The finite transition time of the pressure pulse causes magnetopause oscillations to be weak and elongated relative to established models The magnetopause oscillations are explained wi