Electric dipole radiation at vlf in a uniform warm magneto-plasma

Abstract

The present paper considers the VLF radiation characteristics from a thin dipole antenna in a warm magnetoplasma. Formal solutions are derived for the portions of the dipole radiation resistance due to the thermal modes (Rt) and the whistler mode (Rw). In this derivation the ions are assumed to be cold, and the effects of finite electron temperatures are included by means of a scalar pressure term. Two particular orientations of the dipole are considered (parallel and perpendicular to the static magnetic field line). A detailed analysis is made for frequencies in the range between the electron gyrofrequency (fHe) and the lower-hybrid-resonance frequency (fLHR). Several numerical plots of Rt ∥, and Rw∥, are presented for typical VLF magnetospheric plasma parameters. They show that for frequencies ( f) not close to fLHR, Rt∥, is generally < 2 x 10-1 Rw∥, whereas as f → fLHR, R t , ≃ 10-1 Rw and R t∥ ≃ Rw∥. Using these numerical values of Rt∥, and Rw∥,, the dipole whistler mode radiation efficiences ηw have been estimated for a number of specific cases. In most cases ηw ≳ 70 %, but falls as low as ∼ 38 % at f ≃ f≳ LHR