The Chain Response of the Magnetospheric - and - ground Magnetic Field to Interplanetary Shocks

In response to interplanetary (IP) shocks, magnetic field may decrease/increase (negative/positive response) in nightside magnetosphere, while at high latitudes on the ground it has two phase bipolar variations: preliminary impulse(PI) and main impulse (MI). Using global MHD simulations, we investigate the linkage between the MI phase variation on the ground and the magnetospheric negative response to an IP shock. It is revealed that although the two phenomena occur at largely-separated locations, they are physically related and form a response chain. The velocity disturbances near the flanks of the magnetopause cause the magnetic field to decrease, resulting in a dynamo which thus powers the transient field-aligned currents (FACs). These FACs further generates a pair of ionospheric current vortex, leading to MI variations on the ground. For the first time, we report here the intrinsic physically-related chain response of the magnetospheric - and - ground magnetic field to IP shocks.