<span>The Sun continuously sends plasma and magnetic fields toward Earth, loading the nightside magnetosphere (the magnetotail) with energy and momentum in its stretched magnetic field lines. Under certain conditions this stored energy is suddenly released, producing fast streams of plasma that travel from the magnetotail toward Earth and interact with the ionized upper atmosphere (the ionosphere) through electric currents. On 7 December 2023, six such fast plasma flows were detected by a spacecraft in the magnetotail. By tracing the magnetic field lines, we estimated where each flow connected to the ionosphere. Using ground‑based magnetometers, auroral images, and satellite measurements, we examined how the ionosphere responded to each flow. We show that the repeated impacts of these flows gradually altered the ionospheric current system and auroral activity, ultimately leading to the onset of a substorm.</span>