Foreshock bubbles can modify their solar wind discontinuities enabling secondary transients to form

Solar wind directional discontinuities can generate transient mesoscale structures such as foreshock bubbles and hot flow anomalies (HFAs) upstream of Earth's bow shock. These structures can have a global impact on the near-Earth environment, and understanding their formation conditions is crucial to evaluate their contribution to solar wind-magnetosphere coupling. Here we present the results of a global 2D hybrid-Vlasov simulation (with 3D electromagnetic fields) of the interaction of a rotational discontinuity with near-Earth space, performed with the Vlasiator model. The magnetic field rotates by 90 degrees from ortho-Parker spiral to Parker spiral orientation across the discontinuity. As the discontinuity enters the simulation domain, a foreshock bubble forms duskward of the Sun-Earth line, where the foreshock is initially located. Shortly after the discontinuity makes first contact with the bow shock at the subsolar point, we find that a structure with enhanced temperature and strongly deflected flows develops at the intersection of the discontinuity with the bow shock. This structure displays typical features of an HFA. However, HFA formation requires electric fields pointing towards the discontinuity on at least one side, a condition which is not initially met in our simulation. We demonstrate that the prior generation of the foreshock bubble provides the necessary conditions for HFA formation. We then investigate the evolution of both structures as the discontinuity travels antisunward, showing that the foreshock bubble signatures tend to weaken while the HFA grows. We also report a large-scale bow shock deformation, with the bow shock expanding several Earth radii outward of its initial position within the compressed edge of the foreshock bubble. Our results provide new clues regarding the formation and evolution of large-scale foreshock transients and their impact on the shock.