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The Magnetospheric Multiscale (MMS) spacecraft observed many enhancements of electromagnetic ion cyclotron (EMIC) waves in an event in the late afternoon outer magnetosphere. These enhancements occurred mainly in the troughs of magnetic field intensity associated with a compressional ultralow frequency (ULF) wave. The ULF wave had a period of ∼2–5 min (Pc5 frequency range) and was almost static in the plasma rest frame. The magnetic and ion pressures were in antiphase. They are consistent with mirror-mode type structures. We apply the Wave-Particle Interaction Analyzer method, which can quantitatively investigate the energy transfer between hot anisotropic protons and EMIC waves, to burst-mode data obtained by the four MMS spacecraft. The energy transfer near the cyclotron resonance velocity was identified in the vicinity of the center of troughs of magnetic field intensity, which corresponds to the maxima of ion pressure in the compressional ULF wave. This result is consistent with the idea that the EMIC wave generation is modulated by ULF waves, and preferential locations for the cyclotron resonant energy transfer are the troughs of magnetic field intensity. In these troughs, relatively low resonance velocity due to the lower magnetic field intensity and the enhanced hot proton flux likely contribute to the enhanced energy transfer from hot protons to the EMIC waves by cyclotron resonance. Due to the compressional ULF wave, regions of the cyclotron resonant energy transfer can be narrow (only a few times of the gyroradii of hot resonant protons) in magnetic local time.

[1] Recently, Robinson et al. [2000] presented a brief report on the artificial generation of ULF waves by high power ionospheric modification and their subsequent detection by the Fast Auroral Snapshot ( FAST) spacecraft. The radio frequency "heating'' facility at Tromso was employed to impose a 3-Hz modulation on the current system that constitutes the auroral electrojet, resulting in the injection of field-guided ULF waves into the magnetosphere. The electric and magnetic field signatures of the waves were detected directly by the FAST spacecraft. Furthermore, a signature in the downgoing field-aligned electron flux, also observed by the satellite, was postulated to have resulted from the interaction of the ULF waves with the upper boundary of the ionospheric Alfven resonator. This paper evaluates these results in the context of the prevailing ionospheric conditions during the experiment and discusses the significance of the substorm activity, which occurred during this interval. The technique of artificial ULF wave injection, which can be used to "tag'' narrow flux tubes, could play an important part in overcoming mapping issues between ground-based and space-based observations of phenomena that couple the ionosphere and magnetosphere.