[P-EM14] [EE] Dynamics in magnetosphere and ionosphere

[PEM14-04] Propagation and evolution of electric fields associated with solar wind pressure pulses based on spacecraft and ground-based observations

*高橋 直子¹、笠羽 康正¹、西村 幸敏^2,3、新堀 淳樹⁴、菊池 崇^4,5、堀 智昭⁶、海老原 祐輔⁵、西谷 望⁴ (1.東北大学大学院理学研究科、2.University of California, Los Angeles、3.Boston University、4.名古屋大学宇宙地球環境研究所、5.京都大学生存圏研究所、6.東京大学大学院理学系研究科)

We investigate spatial and temporal evolution of large-scale electric fields in the magnetosphere and ionosphere associated with sudden commencements (SCs) using multi-point equatorial magnetospheric (THEMIS, RBSP, GOES) and ionospheric (C/NOFS) satellites with radars (SuperDARN). A distinct SC event on March 17, 2013 and a statistical analysis of 130 SC events show that the magnetospheric electric field in the equatorial plane propagates from dayside toward nightside as a compressional wave. Estimated tailward propagation speed is about 1000–1100 km/s, which can be explained by 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 Alfvén wave speed. Tailward and downgoing field-aligned Poynting fluxes evaluated from THEMIS and RBSP data support these propagations. 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). 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 pre-midnight or post-midnight regions while maintaining a certain amplitude. The enhancement of duskward electric field is affected by the evolution of the current system associated with the main impulse of SCs.