The dominance of electron plasma waves near a reconnection X‐line region

As previously reported by Oieroset et al. [2000] , the Wind spacecraft made a fortuitous near‐encounter in April 1999 with an active X‐line reconnection region in the geomagnetic tail. The plasma flow signatures included two reversals of bulk flow velocity from earthward to tailward, and then tailward to earthward. We report here on the associated plasma wave observations made concurrently with the near‐encounter with the X‐line. Specifically, we find that emissions at the local upper hybrid frequency intensify greatly for short periods, with amplitudes exceeding 40 mV/m detected in the region. We discuss the upper hybrid bursts' possible importance in the electron diffusion region.