Ionosphere Plasma Response to Magnetopause X-line Evolution for Ideal MHD

Magnetic reconnection plays a fundamental role in transporting energy, momentum, and plasma from the solar wind to the magnetosphere-ionosphere system. During an IMF southward turning, a magnetopause reconnection X-line forms near the magnetic equator region and is considered to drive dayside plasma convection in the magnetosphere-ionosphere system. However, how the azimuthal size of flows at the X-line and in the ionosphere relate to each other, and what mechanisms control the azimuthal flow size remain unclear. In this study, we use the global ideal MHD simulation to address this question using an event during an IMF southward turning. The results reveal that after an IMF southward turning, a strong and localized plasma flow channel emerges near noon in the ionosphere. Interestingly, the flow at the magnetopause X-line is azimuthally much wider than the ionospheric flow. The flow becomes narrower as the flow moves toward the cusp. The narrow flow is not created at the X-line region but is driven by azimuthally localized force directed anti-sunward and toward noon. These findings indicate that dayside ionospheric convection is not solely driven by X-line processes but is instead a result of the forces along the magnetopause and in the cusp. This finding underscores the importance of considering global force distributions when examining reconnection-driven plasma dynamics.