The interaction of a solar wind discontinuity with the backstreaming particles of the Earth’s ion foreshock can generate hot, tenuous plasma transients such as foreshock bubbles (FB) and hot flow anomalies (HFA). These transients are known to have strong effects on the magnetosphere, distorting the magnetopause (MP), either locally during HFAs or globally during FBs. However, previous studies on the global impact of FBs have not been able to determine whether the response stems directly from the transverse scale size of the phenomenon or its fast motion over the magnetosphere. Here we present the observation of an FB and its impact on the magnetosphere from different spacecraft scattered over the dayside magnetosphere. We are able to constrain the size of the transverse scale of an FB from direct observations to be about 10 $R_\mathrm{E}$. We further suggest that a combination of this scale and the motion of the FB over the MP is responsible for the previously reported global response of the dayside magnetosphere.

Hot flow anomalies (HFAs) and foreshock bubbles (FBs) are frequently observed in Earth’s foreshock, which can significantly disturb the bow shock and therefore the magnetosphere-ionosphere system and can accelerate particles. Previous statistical studies have identified the solar wind conditions (high solar wind speed and high Mach number, etc.) that favor their generation. However, backstreaming foreshock ions are expected to most directly control how HFAs and FBs form, whereas the solar wind may partake in the formation process indirectly by determining foreshock ion properties. Using Magnetospheric Multiscale mission and Time History of Events and Macroscale Interactions during Substorms mission, we perform a statistical study of foreshock ion properties around 275 HFAs and FBs. We show that foreshock ions with a high foreshock-to-solar wind density ratio (>~3%), high kinetic energy (>~600eV), large ratio of kinetic energy to thermal energy (>~0.1), and large perpendicular temperature anisotropy (>~1.4) favor HFA and FB formation. We also examine how these properties are related to solar wind conditions: higher solar wind speed and larger (angle between the interplanetary magnetic field and the bow shock normal) favor higher kinetic energy of foreshock ions; foreshock ions are less diffuse at larger ; small , high Mach number, and closeness to the bow shock favor a high foreshock-to-solar wind density ratio. Our results provide further understanding of HFA and FB formation.

We report results of our analysis of a solar wind reconnecting current sheet (RCS) and its solar wind magnetic hole observed on 20 November 2018. In the solar wind, the normal vector to the current sheet plane makes an angle of 32° with the Sun-Earth line. A combination of tilted current sheet plane and foreshock effects cause an asymmetric interaction with the bow shock, such that the structure arrives at the quasi-perpendicular side of the bow shock before the quasi-parallel side. The solar wind flow slowdown and deflection during the bow shock crossing significantly disrupt the reconnection exhausts within the RCS. Unlike localized magnetosheath jets, the solar wind RCS has a global impact on the bow shock and the magnetopause. Plasma flow deflection in the magnetosheath also increases with the passage of the RCS. The magnetic field strength inside the magnetic hole decreases by ~69 percent in the solar wind, with a similar depression rate observed inside the magnetosheath due to this structure. The ion density and temperature both increase within the current sheet to form a roughly pressure balanced structure. Field rotation and change in the dynamic pressure during this event modify the reconnection zones at the magnetopause and cause an inward motion of this boundary.