We use the magnetohydrodynamic (MHD) with embedded particle‐in‐cell model (MHD‐EPIC) to study the Geospace Environment Modeling (GEM) dayside kinetic processes challenge event at 01:50–03:00 UT on 18 November 2015, when the magnetosphere was driven by a steady southward interplanetary magnetic field (IMF). In the MHD‐EPIC simulation, the dayside magnetopause is covered by a PIC code so that the dayside reconnection is properly handled. We compare the magnetic fields and the plasma profiles of the magnetopause crossing with the MMS3 spacecraft observations. Most variables match the observations well in the magnetosphere, in the magnetosheath, and also during the current sheet crossing. The MHD‐EPIC simulation produces flux ropes, and we demonstrate that some magnetic field and plasma features observed by the MMS3 spacecraft can be reproduced by a flux rope crossing event. We use an algorithm to automatically identify the reconnection sites from the simulation results. It turns out that there are usually multiple X‐lines at the magnetopause. By tracing the locations of the X‐lines, we find that the typical moving speed of the X‐line endpoints is about 70 km/s, which is higher than but still comparable with the ground‐based observations.

Using a three‐dimensional (3‐D) global‐scale hybrid code, the Magnetospheric Multiscale (MMS) reconnection event around 02:13 UT on 18 November 2015, highlighted in the Geospace Environment Modeling (GEM) Dayside Kinetic Challenge, is simulated, in which the interplanetary magnetic field (IMF) points southward and the geomagnetic field has a −27° dipole tilt angle. Strong southward plasma jets are found near the magnetopause as a result of the dayside reconnection. Our results indicate that the subsolar magnetopause reconnection X line shifts from the subsolar point toward the Northern Hemisphere due to the effect of the tilted geomagnetic dipole angle, consistent with the MMS observation. Subsequently, the reconnection X lines or sites and reconnection flux ropes above the equator propagate northward along the magnetopause. The formation and global distribution of the X lines and the structure of the magnetopause reconnection are investigated in detail with the simulation. Mirror mode waves are also found in the middle of the magnetosheath downstream of the quasi‐perpendicular shock where the plasma properties are consistent with the mirror instability condition. As a special outcome of the GEM challenge event, the spatial and temporal variations in reconnection, the electromagnetic power spectra, and the associated D‐shaped ion velocity distributions in the simulated reconnection event are compared with the MMS observation.

We have used the AMR-CESE-MHD model to investigate the influences of the IMF B_z and the upstream solar wind dynamic pressure (D_p) on Earth’s magnetopause and bow shock. Our results present that the earthward displacement of the magnetopause increases with the intensity of the IMF B_z. The increase of the northward IMF B_z also brings the magnetopause closer to the Earth even though with a small distance. Our simulation results show that the subsolar bow shock during the southward IMF is much closer to the Earth than during the northward IMF. As the intensity of IMF B_z increases (also the total field strength), the subsolar bow shock moves sunward as the solar wind magnetosonic Mach number decreases. The sunward movement of the subsolar bow shock during southward IMF are much smaller than that during northward IMF, which indicates that the decrease of solar wind magnetosonic Mach number hardly changes the subsolar bow shock location during southward IMF. Our simulations also show that the effects of upstream solar wind dynamic pressure (D_p) changes on both the subsolar magnetopause and bow shock locations are much more significant than those due to the IMF changes, which is consistent with previous studies. However, in our simulations the earthward displacement of the subsolar magnetopause during high solar wind D_p is greater than that predicted by the empirical models.

In this paper, we perform a three-dimensional (3-D) global-scale hybrid simulation to investigate the generation of kinetic Alfvén waves (KAWs) in reconnection at the dayside magnetopause. In the simulation, the magnetopause reconnection takes place due to a self-consistent interaction between the solar wind and Earth's magnetosphere, in which the solar wind is assumed to carry a southward interplanetary magnetic field. As multiple X-line reconnection occurs, shear Alfvénic perturbations are generated from reconnection, which propagate toward polar regions along the magnetic field lines. Our detailed analysis of the electromagnetic characteristics reveals the existence of kinetic Alfvén waves on the ion kinetic scales in these perturbations, in which the parallel electric field is generated. The 3-D structures and the Poynting fluxes in the shear Alfvén waves/KAWs in the global magnetopause are presented. It is shown that these KAWs carry electromagnetic energy into the cusp, which may lead to aurora brightening.

Ion‐scale magnetic reconnection has been observed downstream of the terrestrial quasi‐parallel (Q‐∥) shock. Whether it is driven by interplanetary discontinuities or turbulent Q‐∥ shock, however, is unclear. Using three‐dimensional global hybrid simulation, we investigate the generation of magnetic reconnection downstream of the Q‐∥ shock, while an interplanetary rotational discontinuity (RD) is launched to the bow shock. Cases with various solar wind Alfvén Mach numbers, M_A = 3.0 to 8, and propagation directions of the RD are presented. The propagation direction n is assumed to be in the GSE xz plane and pointing earthward, with n = (−sin(θ₁₂/2),0,−cos(θ₁₂/2)), where θ₁₂ is the angle between the upstream (B₁) and downstream (B₂) magnetic fields across the transmitted RD. It is found that magnetic reconnection occurs inside the RD downstream of the Q‐∥ shock, forming flux ropes extending along the dawn‐dusk direction about tens of ion inertial lengths. Large‐amplitude low‐frequency waves originated from the Q‐∥ shock lead to the bending and squeezing of the field lines around the RD, which play an important role in triggering reconnection inside the RD. As the RD impacts the dayside magnetopause, magnetopause reconnection takes place between the field lines behind the RD and geomagnetic field lines. Nevertheless, no reconnection is found downstream of the Q‐∥ shock itself or outside the RD in the magnetosheath. The existent and structure of reconnection in the magnetosheath are found to strongly depend on the parameters M_A and n. Our simulation shows that ion‐scale magnetic reconnection is driven by an external driver in the form of the compression of an RD around the bow shock and in the magnetosheath, rather than caused by the turbulent Q‐∥ shock alone.

Terrestrial dayside dynamics associated with a southward turning, oblique interplanetary magnetic field (IMF) carried by an interplanetary tangential discontinuity (TD) is investigated by performing a three‐dimensional global‐scale hybrid simulation systematically for cases in which the incoming solar wind TD possesses various magnetic field rotation angles ΔΦ = 90° to 180° and half widths w = 2d_i0 to w = 30d_i0, where d_i0 is the ion inertial length in the solar wind. Overall, the TD is compressed while being transmitted into the magnetosheath, with different compression processes downstream of the quasi‐parallel (Q‐||) and quasi‐perpendicular (Q‐⊥) shocks. It is found that magnetosheath reconnection may take place downstream of both the Q‐|| and Q‐⊥ shocks due to interaction of the directional TD with the bow shock and magnetopause, but the existence of magnetosheath reconnection depends on w and ΔΦ. Magnetosheath flux ropes are formed through three‐dimensional patchy reconnection in the thinned current sheet, with a longer rope lengths under a larger ΔΦ. There exists a dawn‐dusk asymmetry in the spatial extent of the flux ropes, which becomes more significant as ΔΦ decreases. When ΔΦ decreases to 90°, no reconnection flux ropes are found. Magnetopause reconnection is initiated when the magnetic fluxes with a southward turning IMF (on the sunward side) reach the magnetopause, and the magnetopause flux ropes can be mixed with the magnetosheath ones. Our simulation demonstrates that the effects of a southward turning of the IMF may not be a simple field direction change that leads to reconnection only at the magnetopause.