KINETIC ALFVEN WAVES EXCITED BY OBLIQUE MAGNETOHYDRODYNAMIC ALFVEN WAVES IN CORONAL HOLES

Kinetic Alfven waves (KAWs) are small-scale dispersive AWs that can play an important role in particle heating and acceleration of space and solar plasmas. An excitation mechanism for KAWs created by the coupling between large-scale oblique AWs and small-scale KAWs is presented in this paper. Taking into account both the collisional and Landau damping dissipations, the results show that the net growth rate of the excited KAWs increases with their perpendicular wavenumber k(perpendicular to) and reaches maximum at lambda(e)k(perpendicular to) similar to 0.3, where lambda(e) is the electron inertial length. However, for KAWs with shorter perpendicular wavelengths, the net growth rate decreases rapidly due to dissipative effects. The evaluation of the threshold amplitude of the AW implies that for KAWs with lambda(e)k(perpendicular to) < 0.3, the relative threshold amplitude is well below 10%, which is easy to satisfy. In particular, when applying this mechanism to the case of a solar coronal hole containing a dense plume structure, our results show that KAWs with lambda(e)k(perpendicular to) < 0.3 can be not only efficiently excited in the interplume region but also strongly dissipated in the dense plume due to the Landau damping.