Correlations of Proton Energy Spectra and EMIC Waves in the Earth's Equatorial Outer Magnetosphere: SCATHA Satellite Results

A study using 58 days of magnetic field and proton spectra data from the SCATHA (P78-2) satellite has been conducted to evaluate the correlation between electromagnetic ion cyclotron (EMIC) waves and proton fluxes in the Earth's outer magnetosphere. Based on wave power and ellipticity, ɛ, measurements EMIC waves were observed intermittently on 37 days. Among the hundreds of wave occurrences observed, we found no correlations between EMIC waves and proton differential fluxes in the energy bands centered at 0.88, 2.06, 3.60, and 8.80 keV for either parallel or perpendicular components. For energy bands centered at 15.6, 36.0, 71.0, and 133.0 keV there were no correlations between proton parallel differential fluxes and EMIC waves. There were, however, 20 time intervals showing correlations between perpendicular fluxes and EMIC waves. Each of these 20 intervals lasted only several minutes. These intervals were mainly near local noon and in the evening sector. The L values were from 5.6 to 7.5 with magnetic latitudes from -15.6° to 15.4°. The wave frequencies fell in the range 0.16-1.06 Hz, which corresponds to 0.06-0.56 normalized to the local proton gyrofrequency. Nineteen out of 20 had ɛ < 0.0, i.e.,left-hand polarization, and one had ɛ near 0.0, i.e., linear polarization. Linear analysis of the resonant interaction of an individual proton with the observed EMIC waves is consistent with the observed correlations. It would appear that in these rare cases the pitch angle distributions are non-gyrotropic.