Propagation and evolution of electric fields associated with solar wind pressure pulses based on spacecraft and ground-based observations

We investigate spatial and temporal evolution of large-scale electric fields in the magnetosphere and ionosphere associated with sudden commencements (SCs) using multipoint equatorial magnetospheric (THEMIS, RBSP, and GOES) and ionospheric (C/NOFS) satellites with radars (SuperDARN). A distinct SC event on 17 March 2013 shows that the magnetospheric electric field in the equatorial plane propagates from dayside toward nightside as a fast-mode wave. The ionospheric electric field responds ~41 s after the onset of dayside magnetospheric electric field, which can be explained by the propagation of the Alfvén wave along magnetic field lines. The wavelet analysis shows that the Alfvén wave is dominant in the plasmasphere. Poynting fluxes toward the ionosphere support these propagations. From a statistical analysis of response time, tailward propagation speed is estimated at about 1000–1100 km/s. We also statistically derive a spatial distribution and time evolution of the magnetospheric electric field in the dawn-dusk direction (E_y). Our result shows that negative E_y (dawnward) propagates from noon toward the magnetotail, followed by positive E_y (duskward). The propagation characteristics of electric fields in the equatorial plane depend on magnetic local time. At noon, negative E_y lasts for about 1 min, and positive E_y becomes dominant about 2 min after the SC onset. Negative E_y soon attenuates in the nightside region, while the positive E_y propagates fairly well to the premidnight or postmidnight regions while maintaining a certain amplitude. The enhancement of positive E_y is due to the enhancement of magnetospheric convection associated with the main impulse of SCs.