The Cross-Polar Cap Saturation in GUMICS-4 During High Solar Wind Driving

Abstract : It is well known that the Earth's ionospheric cross‐polar cap potential (CPCP) saturates as a response to the solar wind driver especially when the level of driving is high and the interplanetary magnetic field (IMF) is oriented southward. Moreover, previous studies have shown that the upstream Alfvén Mach number may be an important factor in the saturation effect. While the CPCP is often viewed as a measure of the solar wind ‐ magnetosphere ‐ ionosphere ‐coupling the processes associated with the nonlinearity of the coupling remains an open issue. We use the Grand Unified Magnetosphere‐Ionosphere Coupling Simulation (GUMICS‐4) and artificial solar wind data to mimic weak and strong driving in order to study the CPCP response to a wide range of IMF magnitudes (3.5 nT – 30 nT) and upstream Alfvén Mach number values (1.2 – 22). The results provide the first overview of the CPCP saturation in GUMICS‐4 and show that the onset of saturation is strongly dependent on the upstream Alfvén Mach number and the physical processes responsible for the saturation effect might take place both in the Earth's magnetosheath and in the upstream solar wind.