Occurrence of EMIC waves observed by Van Allen Probe B. (a) Wave power spectrogram in the range of 0.1–2 Hz for the 18:00 to 23:00 UT period on 2014 September 12. The magenta, red, and black lines correspond to ion gyrofrequencies for hydrogen, helium, and oxygen, respectively. (b) Time series of the variation (relative to a 100 s local average of the background) parallel magnetic field component in the MFA coordinate system. The most intense oscillations in the magnetic field correspond to EMIC waves. (c) Detailing of an intensified magnetic field variation during the analyzed event shows EMIC wave packets. (d) An interval of 22 s of data showing a wave packet in detail. The central frequency is about 0.6 Hz, and the maximum amplitude of the disturbance is approximately 2 nT.