Low Frequency Waves in Space Plasmas (Invited)

Abstract:

Low frequency waves have been widely observed in space plasmas. They have been classified as Pc 1-5 waves for continuous pulsations and Pi 1-2 waves for impulsive pulsations. The theory of low frequency waves have been developed in the last 50 years. Based on the MHD model, the theory of shear Alfven waves and slow and fast magnetosonic waves was developed for uniform magnetized plasma theory. Then, for non-uniform magnetized plasmas the propagation of fast magnetosonic waves and the deposit of the fast wave energy at the field line resonance location into the shear Alfven waves and slow modes were established. Even within the MHD theory, global stable and unstable MHD eigenmodes are possible due to free energy in the plasma pressure and current density gradients, magnetic field curvature, and pressure anisotropy. Even in the MHD theory, the difficulty in the study of the low frequency wave is how to handle the complex magnetic field geometry. By including the ion gyroradius effects, the kinetic Alfven waves were studied. By including wave-particle resonances, unstable low frequency MHD-type modes such as ballooning-mirror instability and kinetic ballooning have also been developed. In this talk I will give an overview of the low frequency wave theories.