Response of the magnetosphere–ionosphere system to sudden changes in solar wind dynamic pressure

Abstract

The geomagnetic sudden commencement (SC) is a plasma and magnetic field disturbance in the magnetosphere–ionosphere region, which appears as a response of this system to a sudden change in the solar wind dynamic pressures associated with shock and tangential discontinuity of solar wind. As this mechanism seems to be simple, the SC has been widely investigated based on observations in the region from the surface of the Earth to the magnetosphere. A schematic model of the SC was presented by Araki (Solar wind sources of magnetospheric ultra-low-frequency waves. American Geophysical Union, Washington, DC, pp 183–200, 1994), who compiled many observational results and theories related to this phenomenon. Recent advances in supercomputing allow us to present new numerical results including three-dimensional global current systems of the SC which cannot be obtained only by direct observations and theoretical analysis. The simulation study not only confirms the results of a previous model on the initial response of the magnetosphere–ionosphere system to solar wind changes (the preliminary impulse) but also presents new findings on dynamical processes in the magnetosphere–ionosphere system in the period following the initial response (the main impulse). Furthermore, the simulation study reveals the SC sequence in the context of break and recovery of the steady magnetosphere–ionosphere convection system. The transient flow vortex in the flank magnetosphere in the main impulse phase plays an essential role in recovering the convection system. This report describes the SC process from the viewpoint of the state transition of the magnetosphere–ionosphere compound system Tanaka (Space Sci Rev 133:1, https://doi.org/10.1007/s11214-007-9168-4, 2007).