Correlation between λ4278‐Å Optical emissions and a Pc 1 Pearl Event observed at Siple Station, Antarctica

Detailed correlations were observed between the amplitude envelope of Pc 1 pulsations and zenith 4278 N 2 + intensity at Siple Station, Antarctica, ( L =4.2) on August 1, 1977. Conjugate Pc 1 data at Roberval show a similar amplitude envelope and an approximate antiphase relationship. The frequency‐time spectrogram of the ULF data shows none of the increasing dispersion associated with bouncing waves; i.e., the Pc 1 pulsation event is a periodic hydromagnetic emission. Analysis of the time delay between the particle‐induced optical emission and the waves (42 s) using the ion cyclotron resonance theory shows that the delay is consistent with the resonance of Pc 1 and MeV protons near the northern conjugate of the Siple field line. Alternately, resonance theory using He + or O + ions as the interacting hot particles does fit the data if the interaction region is off the equator. The intensity of the measured light is higher than that which can be expected from precipitation of ions of normally observed densities.