Articles | Volume 32, issue 11
Regular paper
13 Nov 2014
Regular paper |  | 13 Nov 2014

Nonlocal nonlinear coupling of kinetic sound waves

O. Lyubchyk and Y. Voitenko

Abstract. We study three-wave resonant interactions among kinetic-scale oblique sound waves in the low-frequency range below the ion cyclotron frequency. The nonlinear eigenmode equation is derived in the framework of a two-fluid plasma model. Because of dispersive modifications at small wavelengths perpendicular to the background magnetic field, these waves become a decay-type mode. We found two decay channels, one into co-propagating product waves (forward decay), and another into counter-propagating product waves (reverse decay). All wavenumbers in the forward decay are similar and hence this decay is local in wavenumber space. On the contrary, the reverse decay generates waves with wavenumbers that are much larger than in the original pump waves and is therefore intrinsically nonlocal. In general, the reverse decay is significantly faster than the forward one, suggesting a nonlocal spectral transport induced by oblique sound waves. Even with low-amplitude sound waves the nonlinear interaction rate is larger than the collisionless dissipation rate. Possible applications regarding acoustic waves observed in the solar corona, solar wind, and topside ionosphere are briefly discussed.

Short summary
Acoustic-type waves are widespread in solar and space plasmas where they contribute to energy transport and release. We discovered a new channel for nonlinear coupling among oblique sound waves with vastly different wavelengths across the background magnetic field. The resulting nonlocal spectral transfer is much faster than the previously known transfer produced by the local interactions among waves with similar wavelengths.