PROPERTIES OF SHORT-WAVELENGTH OBLIQUE ALFVÉN AND SLOW WAVES

Abstract

Linear properties of kinetic Alfv\\'{e}n waves (KAWs) and kinetic slow waves\n(KSWs) are studied in the framework of two-fluid magnetohydrodynamics. We\nobtain the wave dispersion relations that are valid in a wide range of the wave\nfrequency $\\omega $ and plasma-to-magnetic pressure ratio $\\beta $. The KAW\nfrequency can reach and exceed the ion cyclotron frequency at ion kinetic\nscales, whereas the KSW frequency remains sub-cyclotron. At $\\beta \\sim 1$, the\nplasma and magnetic pressure perturbations of both modes are in anti-phase, so\nthat there is nearly no total pressure perturbations. However, these modes\nexhibit also several opposite properties. At high $% \\beta $, the electric\npolarization ratios of KAWs and KSWs are opposite at the ion gyroradius scale,\nwhere KAWs are polarized in sense of electron gyration (right-hand polarized)\nand KSWs are left-hand polarized. The magnetic helicity $\\sigma \\sim 1$ for\nKAWs and $\\sigma \\sim -1$ for KSWs, and the ion Alfv\\'{e}n ratio $R_{Ai}\\ll 1$\nfor KAWs and $R_{Ai}\\gg 1$ for KSWs. We also found transition wavenumbers where\nKAWs change their polarization from left- to right-hand. These new properties\ncan be used to discriminate KAWs and KSWs when interpreting kinetic-scale\nelectromagnetic fluctuations observed in various solar-terrestrial plasmas.\nThis concerns, in particular, identification of modes responsible for\nkinetic-scale pressure-balanced fluctuations and turbulence in the solar wind.\n