Kinetic Alfven wave revisited

We develop a series of new analytical expressions describing the physical properties of the kinetic Alfven wave. The wave becomes strongly compressive when k(perpendicular to)(-1) is of the order of the ion inertial length. Thus, in a low-beta plasma, the kinetic Alfven wave can be compressive at values of k(perpendicular to) for which the dispersion relation departs only slightly from that of the usual MHD Alfven wave. The compression is accompanied by a magnetic field fluctuation delta B-parallel to such that the total pressure perturbation delta p(tot) approximate to 0. Thus the wave undergoes transit-time damping as well as Landau damping; the two effects are comparable if the ion thermal speed is of the order of the Alfven speed. We find that the transverse electric field is elliptically polarized but rotating in the electron sense; this surprising behavior of the polarization of the Alfven branch was discovered numerically by Gary [1986]. We derive a new dispersion relation which explicitly shows how the kinetic Alfven wave takes on some properties of the large-k(perpendicular to) limit of the slow mode. We also derive approximate dispersion relations valid for a multi-ion plasma with differential streaming. We suggest that the kinetic Alfven wave may be responsible for the flattening of density fluctuation spectra observed at large wavenumbers in the corona and in the solar wind. We also find that our derived properties of the kinetic Alfven wave are consistent with its presence in the dissipation range of MHD turbulence [Leamon ef al., 1998a, b].