Saturation of Transpolar Potential for Large Y-component Interplanetary Magnetic Field

This study examines the response of the transpolar potential to a large Y-component interplanetary magnetic field ($B_y$). The transpolar potential responds nonlinearly, saturates, for large IMF in the LFM global MHD simulation. This response occurs for both large $B_y $ and large $B_z$. DMSP satellites data and AMIE results confirm the saturation of the transpolar potential during large $B_y$. The magnitude of the IMF at which the transpolar potential becomes nonlinear is the same for the large $B_y$ cases as for the large $B_z$ cases. The magnitude of the transpolar potential at which it becomes nonlinear is significantly smaller for the large $B_y$ cases than the large $B_z$ cases. This indicates transpolar potential saturation does not depend on the strength of the region 1 current. Rather, these results suggest region 1 current may be limited by the transpolar potential.