Wave-particle interaction around the lower hybrid resonance

Abstract

Wave-particle interaction in the ionosphere is studied theoretically for wave frequencies around the lower hybrid resonance (LHR) frequency. An expression is derived for the growth rate of whistler-mode waves propagating in a magneto-active plasma penetrated by a tenuous beam of nonthermal particles. This expression is an extension of that derived in a previous paper by employing the electrostatic dispersion equation; here, the full-wave dispersion equation is used which reduces to the electrostatic one for large values of refractive index. It is shown that around the LHR frequency there are two regions in the propagation angle θ (the ‘electrostatic’ and ‘electromagnetic’ regions) where growth by the Landau instability process may occur. The maximum growth rate has an abrupt discontinuity just above the LHR frequency and increases rapidly to values several orders of magnitude higher than those below the LHR frequency. Also examined is the influence on the growth rate of the following parameters: the ratio of the temperatures perpendicular and parallel to the background magnetic field T ⊥ T ‖ , the streaming velocity V s of the nonthermal electrons, and the ratio φ 2 of the kinetic energy in the streaming motion to the thermal energy of the streaming electrons. The theory is discussed in relation to LHR noise bands discovered by the Canadian Alouette I satellite and to other VLF signals such as auroral hiss.