“…Many cases of fine‐scale structures in discrete auroras were demonstrated by both spacecraft investigations and ground‐based observations, such as Alfvenic auroras [ Semeter et al , 2008; Frey et al , 2010] and flickering auroras [ Gustavsson et al , 2008; Whiter et al , 2008, 2010; Yaegashi et al , 2011; Kataoka et al , 2011]. While diffuse auroras have been generally regarded as uniform and not discrete structures, fine scale structures were also reported [e.g., Wallis et al , 1979; Pedersen et al , 2007]. Simultaneous optical instruments on the ground and the FAST electron spectrometer found thin auroral stripes extended along the geomagnetic latitudinal directions with a width of about 5 km in dim background luminosity [ Sergienko et al , 2008].…”