ICME impact at Earth with low and typical Mach number plasma characteristics

Abstract. We study how the the Earth's magnetosphere responds to the fluctuating solar wind conditions caused by two different amplitude interplanetary coronal mass ejection (ICME) events by using the Grand Unified Magnetosphere-Ionosphere Coupling Simulation (GUMICS-4). ICME events are known to drive strong geomagnetic disturbances and thus generate conditions that may lead to saturation of the cross-polar cap potential (CPCP). The two ICME events occurred on 15–16 July 2012 and 29–30 April 2014. During the 2012 event, the solar wind upstream values reached up to 35 particles/cm3, speed of 694 km/s, and interplanetary magnetic field of 22 nT. The event of 2014 was a moderate one, with the corresponding upstream values of 30 particles/cm3, 320 km/s and 10 nT. The mean upstream Alfvén Mach number was 2.3 for the 2012 event, while it was 5.8 for the 2014 event. We examine how the Earth's space environment dynamics evolves during both ICME events covering both global and local perspectives. To validate the accuracy of the GUMICS-4 simulation we use satellite data from several missions located in different parts of the magnetosphere. It is shown that the CPCP saturation is affected by the upstream conditions, with strong dependence on the Alfvén Mach number.