A Statistical Study of the Storm-Time Magnetospheric Magnetic Flux Dynamics Using Cross-Scale Observations from the Heliophysics System Observatory (HSO)

Understanding magnetospheric dynamics during geomagnetic storms will improve our preparedness for extreme space weather events. The Heliophysics System Observatory (HSO) allows us to study the dynamics of the magnetosphere from different viewpoints. This study presents the most comprehensive statistical analysis of the magnetic flux dynamics during 33 storm events (storm index SYM-H < -50 nT) between 2015 and 2019, using OMNI, MMS, GOES and Van Allen Probes. The total magnetic flux change relative to the quiet period is found most significant (+25%) during the storm recovery phase. The relative change is most pronounced in the outer magnetosphere, defined as radial distance r ≥ 7 RE, in the region between the ring current and the magnetopause (Chapman-Ferraro) current. A clear dawn-dusk asymmetry in the relative change in total magnetic flux content is further observed. For instance, during the main phase of the storms, when the interplanetary magnetic field turns southward, magnetic flux is on average eroded at the dayside dusk region (-8%) and the nightside dawn region (-14%). The study is concluded by juxtaposing cross-scale observations and global simulations to highlight the roles of magnetic reconnection and global current systems in determining the magnetospheric response to geomagnetic storms.