Effect of perpendicular gradients on the amplification of Auroral Kilometric Radiation in auroral cavities with density depletions

Abstract

The kilometric radiation in the auroral zones of the Earth is investigated with the use of the transfer equation for the intensity of the wave along the trajectory, which is obtained with the formulation of the geometric optics. The components of the dielectric tensor are evaluated along the trajectory, taking into account explicit effects due to the inhomogeneity, and considering both the energetic and the background electron populations. The cyclotron emissivity is evaluated using the locally homogeneous plasma approximation. For frequencies in the vicinity of the electron cyclotron frequency, the calculations are made for a range of initial values of the parallel refractive index which result in significant amplification. The results obtained show that the inclusion of inhomogeneity effects in the evaluation of the components of the dielectric tensor leads to an amplification process which is qualitatively similar to that obtained using the locally homogeneous approximation, in the same range of frequency and initial parallel refractive index, but less efficient, so that the maximum efficiency obtained is nearly 30% of that obtained using the locally homogeneous approximation. Copyright 2008 by the American Geophysical Union.