This article presents case studies of common volume observations of the E region radar aurora obtained with a 30 MHz imaging radar and the optical aurora (green line emissions) recorded by an all sky camera. In addition, in situ rocket electric field measurements in the vicinity of an auroral arc are presented in a separate case study. As inferred from the measurements, the radar aurora in the vicinity of a stable evening auroral arc arises because of the arc's polarization electric fields, which excite the two stream instability and generate electron density irregularities at meter scales. The radar aurora is the backscattering of radar waves from these irregularities.