Determination of the electron distribution in the magnetosphere using hydromagnetic whistlers

As in the case of atmospheric whistlers the electron-density distribution in the magnetosphere can be inferred from the dispersion characteristics of a hydromagnetic wave propagating between hemispheres along a line of force of the earth's magnetic field. Two methods are investigated in this paper, one of which is similar to that developed by Smith and Carpenter and also by Brice for atmospheric whistlers and is found to be more convenient and accurate than the other. The errors involved in this method are investigated by working out a typical example. The two main sources of error are the lack of precision in scaling group bounce periods and the uncertainty in the model taken for the electron distribution in the magnetosphere. If the errors in scaling group bounce periods are ±5%, the equatorial crossing point of the guiding magnetic line of force is determined within an error of ±3% and the electron number density at that point can be determined within a factor of about 2. The errors due to the second source are comparable to those due to the first. The errors arising from the dipole field assumption made in this paper are estimated also; they seem to be comparable with the errors due to the other two sources of error.