THE ROLE OF NONLINEAR COUPLING IN WAVE HEATING OF CORONAL LOOP

摘要

Resonant absorption, first proposed by Ionson, was extensively studied as one of the major candidates for coronal heating, and it is believed that the Alfvenic fluctuation with large amplitudes and gradients established around the resonant layer is essential to this mechanism. On the basis of this point, we investigate the effect of nonlinear coupling in the dissipative layer of a coronal loop driven by azimuthal footpoint motions with two frequencies. With a three-wave interaction model, we find that the pump mode (ω_2, k_2) could be intensively modulated by the large-amplitude resonant fluctuation v_1 accumulated localizedly around the dissipative layer. The derived modified wavenumber (k_m > 10~2k_2) implies strong phase mixing and the consequent phase modulation dissipation, and the resulting damping length L_d is smaller than the loop length L in the active regions, which may be instructive to explain the recent observation on the localized heating at the footpoints of coronal loops.