Magnetospheric response to southward IMF turning: insights from global models and data analysis

We study the magnetospheric response to solar wind discontinuities with a southward interplanetary magnetic field (IMF) turning. We find two events characterized by a strong positive IMF Bz before the discontinuity and a strong negative Bz after the discontinuity. The magnetosphere stays in quiet conditions until the southward turning in both cases, then the dayside reconnection starts and the electromagnetic energy is accumulated in the magnetotail. We simulate these cases using several MHD models and compare numerical predictions of the global parameters such as the magnetopause standoff distance, open flux in the polar cap, auroral indices, and cross polar cap potential. We also make several runs of one model with different spatial resolutions and ionospheric conductivities. Summarizing this study, we discuss the differences between the MHD models and speculate about the reasons why one model is able to better predict observations than the other. We also discuss the reasons for different magnetospheric responses observed in two cases.