Kinetic Alfven wave revisited

We develop a series of new analytical expressions describing the physical p roperties of the kinetic Alfven wave. The wave becomes strongly compressive when k(perpendicular to)(-1) is of the order of the ion inertial length. T hus, in a low-beta plasma, the kinetic Alfven wave can be compressive at va lues of k(perpendicular to) for which the dispersion relation departs only slightly from that of the usual MHD Alfven wave. The compression is accompa nied by a magnetic field fluctuation delta B-parallel to such that the tota l pressure perturbation delta p(tot) approximate to 0. Thus the wave underg oes transit-time damping as well as Landau damping; the two effects are com parable if the ion thermal speed is of the order of the Alfven speed. We fi nd that the transverse electric field is elliptically polarized but rotatin g in the electron sense; this surprising behavior of the polarization of th e Alfven branch was discovered numerically by Gary [1986]. We derive a new dispersion relation which explicitly shows how the kinetic Alfven wave take s on some properties of the large-k(perpendicular to) limit of the slow mod e. We also derive approximate dispersion relations valid for a multi-ion pl asma with differential streaming. We suggest that the kinetic Alfven wave m ay be responsible for the flattening of density fluctuation spectra observe d at large wavenumbers in the corona and in the solar wind. We also find th at our derived properties of the kinetic Alfven wave are consistent with it s presence in the dissipation range of MHD turbulence [Leamon ef al., 1998a , b].