Simultaneous ground‐satellite optical observations of postnoon shock aurora in the Southern Hemisphere

<jats:p>On 14 June 2005, a transient postnoon shock aurora, induced by an interplanetary (IP) shock, was observed simultaneously with the FUV imager onboard the IMAGE satellite and the all‐sky imager (ASI) at the South Pole Station (−74.3° magnetic latitude (MLAT), ∼15 magnetic local time). The global evolution of the shock aurora was identified by the FUV, whereas the detailed spatial‐temporal structure was identified by the ASI. Both optical emissions for the shock aurora showed a reasonable agreement in a common field of view. During the transient auroral brightenings in the dayside oval detected by the FUV, a two‐step development of the shock aurora was identified by the ASI in the afternoon sector of the oval. Just after the IP shock, the ASI first observed a diffuse 557.7 nm aurora expanding duskward at the equatorward edge of the oval (−70° to −73° MLAT). About 5 min later, new discrete auroral forms (arcs) were detected in the middle of the oval (−73° to −76° MLAT) by both 557.7 nm and 630.0 nm ASI images. The discrete arcs developed with relatively brighter emissions, and had a lifetime of the order of 10 min, during the main impulse (MI) of geomagnetic sudden commencement. The spectrographic auroral imagers onboard the IMAGE satellite indicated that proton precipitation played an effective role in the first shock auroral emission observed with the ASI, while intense electron precipitation played an effective role in the second one. Mechanisms of the first and second postnoon shock auroras presented here are speculated to be associated with the wave‐particle interaction process, and the field‐aligned acceleration process in the region of the MI‐related upward field‐aligned currents, respectively.</jats:p>