Freja observations of a ten‐meter boundary within monoenergetic auroral electron precipitation

A ∼2‐ms transition in auroral electron precipitation observed by the TESP electron spectrometer on Freja is described. The lack of significant pitch‐angle dependent velocity dispersion in the observations implies that the transition is a ∼10‐m spatial, rather than temporal, boundary. There is no evidence of associated changes in the accelerating potential. Either the source population, or the mechanism allowing entry of the source population to the acceleration region, must provide for the sharp observed transitions. The energy fluxes are such that the regions of stronger precipitation are marginally visible arcs.