ENHANCED DAMPING OF ALFVEN WAVES IN THE SOLAR CORONA BY A TURBULENT WAVE SPECTRUM

The effect of a spectrum of Alfven waves on the rate of dissipation of a shear Alfven wave is calculated. It is demonstrated numerically that as the classical resistivity-eta and classical viscosity-mu become small, the damping rate of the Alfven wave remains large and depends only on the amplitude-phi-0 of the scalar potential of the wave spectrum and the wavenumber k of the Alfven wave. Importantly, the damping rate is virtually independent of eta and mu. The wave spectrum need not be turbulent or stochastic to affect the damping rate. The dissipation rate is nonlinearly enhanced by nonstochastic spectra, as well as by stochastic spectra, as long as two criteria are met. First, the perpendicular magnetic field B(perpendicular-to 0) associated with Alfven wave spectrum must exceed a collision-frequency-dependent threshold, B(perpendicular-to 0)/B0 > (nu/OMEGA(e))(k(perpendicular-to 0) rho(i))beta - 1/2, where nu is the electron-ion collision frequency, OMEGA(e) = eB0/mc is the electron cyclotron frequency in the ambient magnetic field B0, k(perpendicular-to 0) is the perpendicular wavenumber of the waves comprising the background spectrum, rho(i) is the ion gyroradius, and beta = 4-pi-nT/B0(2) is the ratio of the plasma pressure to the magnetic field pressure. Second, for nonstochastic spectra only, B(perpendicular-to 0) must exceed a threshold proportional to the parallel wavenumber k(parallel-to) of the shear Alfven wave, B(perpendicular-to 0/B0 > (k(parallel-to/k(perpendicular-to 0). There is no parallel wavenumber threshold for enhanced damping by stochastic spectra. These conditions can be easily satisfied in the solar corona, and, as a consequence, the damping rate of Alfven waves is much larger than the classical collisional damping rate.