Response of Magnetospheric Convection to the Southward Turning of the IMF in Fast and Slow Solar Wind Streams

Solar wind–magnetosphere interaction is a major driver of global plasma convection in planetary magnetospheres. In Earth's magnetosphere, this convection is governed by magnetic reconnection on the dayside and nightside. Dayside reconnection alone can rapidly re‐establish convection within closed field lines, typically within 10–20 min following a southward turning of the interplanetary magnetic field (IMF). In this study, we show that solar wind speed strongly regulates the evolution and structure of this convection. Using global magnetohydrodynamic (MHD) simulations under the condition, we compare the magnetospheric response to southward IMF turnings under fast (800 km/s) and slow (400 km/s) solar wind streams. In the fast stream case, enhanced convection extends from the dayside magnetopause to 20 R_E down the magnetotail within 15 min, compared to approximately 20 min in the slow stream case. The fast stream also drives deeper and more intense convection, accompanied by stronger Region 1 field‐aligned currents (FACs) and enhanced flow shear in the low‐latitude boundary layer. In both fast and slow wind cases, the induced convection exhibits discrete spatial and temporal channels. These results demonstrate that solar wind speed is a key parameter controlling the development of induced magnetosphere convection, with important implications for global solar wind– magnetosphere coupling.