Magnetic field and medium‐energy ion (E > 4 keV) data acquired by the AMPTE CCE spacecraft have been used to study magnetospheric ULF waves observed during the unusually strong magnetospheric compression event of November 1 (day 306), 1984. Although the spacecraft does not carry an electric field experiment, a method has been developed to infer the electric field of ULF waves from the particle data, based on the gyration acceleration mechanism. We have found three types of waves: (1) a 10‐ to 15‐min wave with perturbations in the magnetic field intensity and in the flux of ions, (2) a 3‐ to 5‐min standing Alfvén wave with perturbations in the azimuthal magnetic field component and in the radial component of the electric field, and (3) a 2‐ to 5‐min irregular disturbance near the magnetopause which involves all components of the magnetic field and the intensity of the ion flux. The origin of the 10‐ to 15‐min compressional wave is not clear, although a global fast‐mode cavity resonance is one possibility among others. Since the frequency of the compressional wave is much lower than that of the Alfvén wave, the simultaneous presence of the two waves cannot be described by the coupling of a global cavity resonance to a standing Alfvén wave. The magnetopause disturbance, which has frequency components similar to the standing Alfvén wave, has some properties inconsistent with an azimuthally propagating standing wave. The Alfvén wave observed throughout the outer magnetosphere may be attributed to the transient response of the field lines to a series of externally applied pressure disturbances.
