Non linear effects associated with kinetic Alfvén wave in solar wind plasmas.

English Abstract:

The nonlinear phenomena are of striking importance in understanding the particle acceleration, heating and turbulence in the interplanetary space. Alfvén waves are known to be the exact solution of the ideal magnetohydrodynamic (MHD) system and when this MHD Alfvén wave develops a large perpendicular wave number transverse to the ambient magnetic field it creates kinetic Alfvén wave (KAW). These waves may be responsible for accelerating the solar wind and powering the solar wind turbulence. Plasma contains a variety of low frequency modes like ion acoustic, magnetosonic mode and even the low frequency KAW. The ponderomotive force of (relatively high frequency, high power) pump KAW may be used to excite the low frequency KAW. This is the motivation of the present work to analyze the nonlinear dynamics of relatively high frequency pump KAW in the presence of comparatively low frequency KAW perturbation and its effect on the solar wind turbulence. For this purpose the dynamical equations to analyze the nonlinear dynamics of relatively high frequency pump KAW in the presence of comparatively low frequency KAW perturbation are derived. The numerical solution has been carried out for the coupled system of equations by using the pseudospectral method for space integration and finite difference method along with the predictor corrector scheme for the evolution in time. The coupled system of nonlinear dynamical equations is analyzed to study the nonlinear effects associated with pump KAW and the resulting turbulent spectra at 1 AU. The averaged power spectrum in the quasisteady state (ensemble contains 10 spectra) obtained follows the Kolmogorov scaling which further steepens after k>1. Therefore, this nonlinear interaction due to KAWs may lead to the distribution of energy among the large and intermediate wavenumbers at k>1[ Saharoui et al., 2010; Howes et al. 2008]. Energy transfer is implicated by the spectral index followed by the turbulent energy spectrum. The process of filamentation attributed to the energy transfer amongst the nonlinearly interacting modes is also studied. The present model may have some applicability to understand the initiation of turbulence in the solar wind.

 References

1. Howes, G. G. et al.: 2008, J. Geophys. Res., 113, A05103. 
2. Sahraoui, F. et al.: 2010, Phys.Rev. Lett. 105, 131101.