Joint observations of the large-scale ULF wave activity from space to ground associated with the solar wind dynamic pressure enhancement

This study reports the rare ultralow-frequency (ULF) wave activity associated with the solar wind dynamic pressure enhancement that was successively observed by the GOES-17 (Geostationary Operational Environmental Satellite) in the magnetosphere, the CSES (China Seismo-Electromagnetic Satellite) in the ionosphere, and the THEMIS ground-based observatories (GBO) GAKO and EAGL in the Earth’s polar region during the main phase of an intense storm on 4 November 2021. Along with the enhanced-pressure solar wind moving tailward, the geomagnetic field structure experienced a large-scale change. From dawn/dusk sides to midnight, the GAKO, EAGL, and GOES-17 sequentially observed the ULF waves in a frequency range of 0.04–0.36 Hz at L shells of ∼5.07, 6.29, and 5.67, respectively. CSES also observed the ULF wave event with the same frequency ranges at wide L-shells of 2.52–6.22 in the nightside ionosphere. The analysis results show that the ULF waves at ionospheric altitude were mixed toroidal-poloidal mode waves. Comparing the ULF waves observed in different regions, we infer that the nightside ULF waves were directly or indirectly excited by the solar wind dynamic pressure increase: in the area of L-shells ∼2.52–6.29, the magnetic field line resonances (FLRs) driven by the solar wind dynamic pressure increase is an essential excitation source; on the other hand, around L∼3.29, the ULF waves can also be excited by the outward expansion of the plasmapause owing to the decrease of the magnetospheric convection, and in the region of L-shells ∼5.19–6.29, the ULF waves are also likely excited by the ion cyclotron instabilities driven by the solar wind dynamic pressure increase.