Determination of hydrogen ion concentration, electron density, and proton gyrofrequency from the dispersion of proton whistlers

Abstract

In this paper we discuss a method for determining H+ concentration, electron number density, and proton gyrofrequency in the vicinity of a satellite by measurements of the asymptotic frequency-time profile of a proton whistler near the proton gyrofrequency. This new technique is applied to proton whistlers received by the Injun 3 VLF receiver. The calculated values of H+ concentration and electron density are shown to be in good agreement with measurements by other experimenters at similar altitudes, latitudes, and local times. B values calculated from the proton gyrofrequency are compared with values calculated from the Jensen and Cain expansion for the geomagnetic field. It is shown that the wave energy of a proton whistler is guided very nearly along the geomagnetic field and that the parallel component of the group velocity is closely approximated by the group velocity for longitudinal propagation. It is found that for frequencies near the proton gyrofrequency at the satellite the kernel multiplying n(H+)½ in the travel-time integral is large only in the region near the satellite. Assuming that the H+ concentration is uniform within this region, an expression is derived for the travel time of a proton whistler near the proton gyrofrequency. The H+ concentration and proton gyrofrequency are obtained by fitting this theoretical frequency-time expression to observed proton whistler signals. By combining this method for determining n(H+) with the crossover frequency method for determining α1 = n(H+)/ne the electron density can also be determined.