The Earth's magnetosphere and its bow shock, which is formed by the interaction of the supersonic solar wind with the terrestrial magnetic field, constitute a rich natural laboratory enabling in situ investigations of universal plasma processes. Under suitable interplanetary magnetic field conditions, a foreshock with intense wave activity forms upstream of the bow shock. So-called 30 s waves, named after their typical period at Earth, are the dominant wave mode in the foreshock and play an important role in modulating the shape of the shock front and affect particle reflection at the shock. These waves are also observed inside the magnetosphere and down to the Earth's surface, but how they are transmitted through the bow shock remains unknown. By combining state-of-the-art global numerical simulations and spacecraft observations, we demonstrate that the interaction of foreshock waves with the shock generates earthward-propagating, fast-mode waves, which reach the magnetosphere. These findings give crucial insight into the interaction of waves with collisionless shocks in general and their impact on the downstream medium.

Departamento de Ciencias Espaciales Instituto de Geofísica Universidad Nacional Autónoma de México Mexico City Mexico

Department of Earth and Planetary Science Graduate School of Science University of Tokyo Tokyo Japan

Department of Physics University of Helsinki Helsinki Finland

Finnish Meteorological Institute Helsinki Finland

Institute of Atmospheric Physics Czech Academy of Sciences Prague Czech Republic

Mullard Space Science Laboratory University College London Dorking UK

Radio Research Institute National Institute of Information and Communication Technology Tokyo Japan

Space Research Institute Austrian Academy of Sciences Graz Austria

Swedish Institute of Space Physics Uppsala Sweden

The Johns Hopkins University Applied Physics Laboratory Laurel MD USA

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