Dayside Shock Aurora at the Beginning of the May 2024 Superstorm: South Pole–THEMIS Spacecraft Conjunction

The impact of interplanetary (IP) shocks on the Earth's magnetosphere manifests itself as global, dynamic disturbances in the magnetosphere‐ionosphere system. Shock aurorae, which are one of the IP shock‐driven disturbances, are a transient auroral emission that initially brightens near the local noon region and then expands along the auroral oval. Although some generation mechanisms have been suggested, direct in situ measurements from the magnetospheric source region of shock aurora observed in the ionosphere are required to determine which mechanism(s) causes it more precisely. In this paper, we present a fortuitous event when the THEMIS spacecraft was situated in/around the outer magnetospheric source region (∼8–10 R E ) of dayside shock aurora at the beginning of the May 2024 superstorm. After the IP shock arrival at the Earth, a white‐light all‐sky camera (ASC) at the South Pole Station observed a two‐step evolution of dayside shock aurora: Diffuse‐type auroral emissions appeared within the initial 1–2 min, and then it was followed by discrete‐type emissions with suddenly emerging ray structures. The 2‐Hz sampling ASC data, for the first time, revealed pulsating aurora (PsA) signatures embedded in the diffuse‐type shock aurora. During the shock PsA interval, THEMIS observed IP shock‐driven dynamics of the magnetosphere, including rapid compression, fast mode waves, transient magnetopause crossings, and damping oscillations. The IP shock also excited/intensified chorus emissions, being a likely driver of the luminosity variation in the shock PsA area. Our conjugate space‐ground observations provide evidence for a more convincing link between IP shock‐driven chorus waves and dayside shock PsA.