2D structure of foreshock driven Pc5 ULF waves observed by THEMIS satellites and ground-based imager conjunction

Foreshock transients can generate significant compressions and rarefactions in front of the bow shock, in an absence of dynamic pressure variation in the pristine solar wind. Recently, in situ observations found that foreshock transients were able to drive magnetospheric Pc5-band (150-600s) ultra-low frequency (ULF) waves, likely in the same manner as interplanetary shocks but with a localized dawn-dusk extent. Those foreshock-transient driven Pc5 waves included both compressional waves and field line resonances (FLRs) in the dayside magnetosphere. However, it is difficult to measure spatial structure of ULF waves by a small number of satellites. We identified foreshock-transient driven Pc5 waves and measured their 2D structure, by utilizing coordinated observation by the THEMIS satellites and All Sky Imager (ASI) at South Pole. In this work, two Pc5 waves in the dayside magnetosphere are reported. We found that these two Pc5 waves were FLRs and driven by foreshock transients. The ground-based ASI at South Pole showed that periodical poleward moving east-west arcs had the same frequencies and occurred simultaneously near the footprints of the FLRs. It indicates that they were the ionospheric/auroral signature of the FLRs. The 2-d imaging further allowed to measure azimuthal distribution of the FLRs in the magnetosphere and their north-south width in the ionosphere. The results showed that the FLRs distribute symmetrically in the pre- and post- noon with out-of-phase oscillations, as the odd toroidal mode behaviors, in the equatorial plane. The entire and fine structures of the poleward moving east-west arcs also indicated the toroidal wave numbers of FLRs. Besides, in the ionosphere, the width of FLRs extends 3 degrees in latitude.