Foreshock transient signatures upstream and downstream of the shock

The interaction of solar wind directional discontinuities with a shock can give rise to large-scale transient structures such as hot flow anomalies and foreshock bubbles. These transients play an important role in particle acceleration, and, when they are formed at Earth's bow shock, can have a global impact on near-Earth space. The properties of foreshock transients upstream of the shock have been extensively studied, and a number of recent studies have started taking a closer look at their signatures in the magnetosheath. There however often remain ambiguities as to whether a structure is observed upstream or downstream of the shock, which cannot be resolved with single-point or closely-spaced multi-spacecraft observations. Foreshock transient properties strongly depart from typical solar wind values, and vary widely from one event to another. It can therefore be difficult to conclude with certainty on which side of the shock a set of observations is made without having reference upstream measurements. To complicate matters further, the bow shock moves in response to the foreshock transient’s varying properties, which can lead to boundary crossings embedded within the transient's observations. In this work, we leverage 2D global numerical simulations performed with the hybrid-Vlasov Vlasiator model to get a global view of the interaction of foreshock transients with Earth's bow shock and compare their properties upstream and downstream of the shock. We investigate how foreshock transient signatures change as they are processed through the shock and compare ion energy spectrograms and velocity distribution functions on both sides of the shock. We aim to identify signatures which could be then used to distinguish between upstream and downstream observations. We test our findings on events previously reported in the literature. Determining whether a foreshock transient is observed before or after its interaction with the shock is crucial to evaluate its impact on the magnetosphere, as a change in e.g. dynamic pressure variations can lead to a different amplitude in the response of the magnetopause.