  In the vicinity of Earth's orbit, the typical solar wind Alfv\'{e}n Mach
number exceeds 5, and the super-Alfv\'{e}nic solar wind drives a conventional
magnetosphere configuration. However, at the ejecta phase of an interplanetary
coronal mass ejection (ICME) event, the Alfv\'{e}n Mach number may experience a
significant reduction due to the intensified interplanetary magnetic field
(IMF) strength and decreased density. On 24 April 2023, an ICME reached Earth's
orbit. The solar wind density dropped to as low as 0.3 amu/cc while the IMF
strength is about 25 nT. As a result, the solar wind flow transitions to a
sub-Alfv\'{e}nic state with an Alfv\'{e}n Mach number of 0.4, providing
opportunities to investigate the interaction of planetary magnetospheres with
low Mach number solar wind. We carry out global simulations to investigate the
responses of Earth's magnetosphere to the sub-Alfv\'{e}nic ICME ejecta. The
global magnetohydrodynamic (MHD) simulation results show the formation of
Alfv\'{e}n wings as the solar wind becomes sub-Alfv\'{e}nic. Furthermore, the
sub-Alfv\'{e}nic period was characterized by the dominance of IMF By component,
causing the Alfv\'{e}n wings to extend towards the dawn and dusk sides. In this
paper, we present the structures of the magnetic field, plasma flow, and
current system around the Alfv\'{e}n wings. The global magnetospheric
convection under the sub-Alfv\'{e}nic solar wind condition is discussed in
depth. Our results achieve a new level of understanding about the interaction
between a magnetized body and sub-Alfv\'{e}nic upstream conditions, and provide
guidance for future observations.
