Universal time influence on stormtime magnetosphere ionosphere coupling

Geomagnetic storms, triggered by solar eruptions, can disrupt satellites, GPS, and power grids, affecting daily life and technology. To understand storm effects, previous studies have been primarily focusing on the their dependence on interplanetary driving conditions. Recent studies start to reveal that the same driving conditions can produce totally different consequences depending on when the storm starts. Earth’s magnetic field is misaligned and offset from its rotational axis, creating a "wobble" that causes daily variations in how much solar ultraviolet (EUV) light reaches the northern and southern polar regions. These variations in EUV exposure can influence the ionosphere and its interaction with the magnetosphere. It is impractical to explore the UT effects in observations because real solar wind conditions never exactly reproduce themselves. This study adopts a physics based fully coupled whole geospace model --- Multiscale Atmosphere-Geospace Environment (MAGE), to explore the causal relationship between UT and storm effects. Using MAGE, we analyzed a major geomagnetic storm and found that the storm’s arrival time strongly affects differences between the Northern and Southern Hemispheres. The activity of auroral electric currents (electrojets) also depends on when the storm arrives.