Equatorward moving auroral signatures of a flow burst observed prior to auroral onset

We present observations of a substorm that occurred on February 25, 2008. Auroral onset was observed with a multi‐spectral ( λ = 427.8, 557.7 and 630.0 nm) and white light all sky imager at Gillam, Canada. An equatorward moving diffuse auroral patch was observed in the λ = 630.0 nm images at least six minutes prior to auroral onset. This form emerged from the background noise poleward of the eventual onset arc and intensified as it moved …