Excitation of EMIC waves detected by the Van Allen Probes on 28 April 2013

We report the wave observations, associated plasma measurements, and linear theory testing of electromagnetic ion cyclotron (EMIC) wave events observed by the Van Allen Probes on 28 April 2013. The wave events are detected in their generation regions as three individual events in two consecutive orbits of Van Allen Probe-A, while the other spacecraft, B, does not detect any significant EMIC wave activity during this period. Three overlapping H+ populations are observed around the plasmapause when the waves are excited. The difference between the observational EMIC wave growth parameter (Sigma(h)) and the theoretical EMIC instability parameter (S-h) is significantly raised, on average, to 0.10 +/- 0.01, 0.15 +/- 0.02, and 0.07 +/- 0.02 during the three wave events, respectively. On Van Allen Probe-B, this difference never exceeds 0. Compared to linear theory (Sigma(h)>S-h), the waves are only excited for elevated thresholds.