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High‐speed jets (HSJs) are commonly observed in the Earth's magnetosheath. The HSJs can drive shock‐like bow waves when compressing the ambient plasma, which are important for the HSJ's evolution and the energization of charged particles. Here we present the first two‐dimensional hybrid simulation of the formation and evolution of jet‐driven bow waves. The simulated bow waves exhibit localized enhanced magnetic field and ion density, with their peaks separated by the order of ion inertial length. The bow waves are formed when a super‐magnetosonic HSJ encounters a magnetic structure with the magnetic field nearly perpendicular to the HSJ's velocity. The magnetic field structure acts as an obstacle to deflect and decelerate the jet, causing the pile up of ions on the jet side and the compression of the magnetic structure on the downstream side. Our study explains the observed properties of bow waves, and helps to better understand the evolution of HSJs. Plain Language Summary: When the solar wind interacts with the Earth's magnetic field, it creates a bow shock in front of the magnetosphere. The bow shock slows down and heats up the solar wind plasma, creating a turbulent area known as the magnetosheath. Sometimes, high‐speed jets (HSJ), observed as high velocity and density pulses, are detected in the magnetosheath. The HSJs can transfer the solar wind plasma through the magnetosheath and potentially affect the near‐Earth space where satellites orbit. Recent studies have found that the HSJs can drive shock‐like bow waves at their front. The bow waves can accelerate and heat up plasma, similar to the primary shock wave, and they play an important role in the evolution of the HSJs. In this study, we present the first simulation result concerning the formation and evolution of the bow waves, which will help us to better understand the HSJs and the magnetosheath dynamics. Key Points: We study the formation and evolution of jet‐driven bow waves with the two‐dimensional hybrid model for the first timePlasma piles up at the ramp of compressed magnetic field, causing separated peaks of density and magnetic field at the bow waveThe magnetic field structure acts as an obstacle to decelerate jet, causing the pile up of jet ions at the leading edge [ABSTRACT FROM AUTHOR]

An important discovery of MESSENGER is the occurrence of dayside disappearing magnetosphere (DDM) events that occur when the solar wind dynamic pressure is extremely high and the interplanetary magnetic field (IMF) is both intense and southward. In this study, we investigate the DDM events at Mercury under extreme solar wind conditions using a three‐dimensional (3‐D) global hybrid simulation model. Our results show that when the solar wind dynamic pressure is 107 nPa and the magnitude of the purely southward IMF is 50 nT, most of the dayside magnetosphere disappears within 10 s after the interaction between the solar wind and the planetary magnetic field starts. During the DDM event, the ion flux is significantly enhanced at most of the planetary dayside surface and reaches its maximum value of about 1010 cm−2 s−1 at the low‐latitude surface, which is much larger than that under normal solar wind conditions. During the DDM events, the dayside bow shock mostly disappears for about 9 s and then reappears. Moreover, the time evolution of magnetopause standoff distance under different solar wind conditions is also studied. When the solar wind dynamic pressure exceeds 25 nPa and the IMF is purely southward, a part of the dayside magnetosphere disappears. Under the same IMF, the higher the solar wind dynamic pressure, the faster the magnetopause standoff distance reaches the planetary surface. When the solar wind conditions are normal (with a dynamic pressure of 8 nPa) or the IMF is purely northward, the dayside magnetosphere does not disappear. The results provide a clear physical image of DDM events from a 3‐D perspective. Plain Language Summary: Mercury has a significant, and apparently global, magnetic field. The planetary magnetic interacts with the solar wind originating from the Sun, creating a magnetosphere. However, it has been observed that the dayside part of the planetary magnetosphere can disappear, which is referred to as dayside disappearing magnetosphere (DDM) events. These events normally occur when the solar wind dynamic pressure is extremely high and the magnetic field in the solar wind is both intense and southward. In this study, we use computer simulations to investigate the DDM events at Mercury under extreme solar wind conditions. Our results show that most of the dayside magnetosphere disappears after the interaction between the extreme solar wind and the planetary magnetic field, leading to a significant enhancement in the precipitation of ion flux on the planetary surface. Moreover, the temporal evolution of the dayside magnetosphere's size under different solar wind conditions was also studied. Under the same solar wind magnetic field, the higher the solar wind dynamic pressure, the smaller the magnetosphere. The results provide a clear physical image of DDM events from a 3‐D perspective. Key Points: Mercury's disappearing dayside magnetosphere event under extreme solar wind conditions is studied by using 3‐D global hybrid simulationsMost of the dayside magnetosphere, even the dayside bow shock, disappears shortly after the interaction between the extreme solar wind and the planetary magnetic fieldIon precipitation on the planetary surface and the time evolution of magnetopause standoff distance under different solar wind conditions are also studied [ABSTRACT FROM AUTHOR]

High‐speed jets (HSJs) are frequently observed downstream of a quasi‐parallel bow shock, and they are considered to play important roles in the coupling of the solar wind, the magnetosheath, and the magnetosphere. Using two‐dimensional hybrid simulations, we study the formation of HSJs in quasi‐parallel shocks with different shock angles (θBn). The interaction of the upstream compressive structures that are inhomogeneous in the direction perpendicular to the background magnetic field and the shock front leads to the shock ripples, and then the downstream HSJs. In a parallel shock with the shock angle θBn = 0°, the interaction regions of the upstream compressive structures with the shock front don't change with time. The shock ripples remain in the same regions of the shock front, and then the HSJs can develop into large‐scale sizes, especially under low plasma β or high Mach number (MA). While in a quasi‐parallel shock with a non‐zero shock angle, the interaction regions of the upstream compressive structures with the shock front move along the shock front. The shock ripples change with time, and the scale size of the downstream HSJs becomes smaller with the increase of the shock angle. Key Points: 2‐D hybrid simulations are performed to study the formation of downstream high‐speed jets (HSJs) and ripples in quasi‐parallel shocks due to the interaction between upstream structures and the shock frontIn a parallel shock, the shock ripples remain in the same regions of the shock front, and large‐scale HSJs can form downstream of the ripplesIn a quasi‐parallel shock, the shock ripples move along the shock front and the downstream HSJs become smaller as the shock angle increases [ABSTRACT FROM AUTHOR]

High‐speed jets (HSJs) occur frequently in Earth's magnetosheath downstream of the quasiparallel bow shock. They have great impacts on the magnetosheath and the magnetosphere. Using two‐dimensional global hybrid simulations, we investigate the formation and evolution of HSJs with different solar wind conditions. When the quasi‐parallel shock is formed, HSJs begin to appear in the quasi‐parallel magnetosheath. Some elongated HSJs formed at the quasi‐parallel bow shock extend toward the quasi‐perpendicular magnetosheath along with the background magnetosheath flow. As the elongated HSJs moves in the magnetosheath, filamentary structures of the velocity, ion density, and temperature occur in the magnetosheath. The filamentary structures are the traces of HSJs moving in the magnetosheath. Moreover, the Kelvin‐Helmholtz instability can be excited at HSJs, which causes meandering of HSJs. When the interplanetary magnetic field is aligned to the solar wind velocity, the large‐scale HSJs with a parallel (perpendicular) scale size of about 2.5 RE (0.3 RE) are formed at the magnetosheath where the θBn is approaching zero. Then, some HSJs converge, leading to the formation of even larger HSJs with a parallel (perpendicular) scale size of 5 RE (0.6 RE). Key Points: 2‐D global hybrid simulations are performed to study quasi‐parallel magnetosheath high‐speed jets (HSJs)The elongated HSJs formed at the quasi‐parallel shock extend toward the quasi‐perpendicular magnetosheath, and the traces of HSJs are filamentary structuresThe solar wind conditions and the convergence of several HSJs lead to the formation of a large‐scale HSJ [ABSTRACT FROM AUTHOR]