Nonlinear propagation of kinetic Alfvén wave and turbulent spectrum in reconnection region of magnetotail

Abstract

Kinetic Alfvén waves (KAWs) are known to play an important role in magnetic reconnection as well as in turbulence. In the present work, we have derived the dynamical equation of KAWs propagating through Harris sheet. It is assumed that background density gets modified due to nonlinearity and background field gets modified due to the presence of Harris sheet. This nonlinear dynamical equation is then solved semi-analytically as well as numerically. Due to the presence of background density and field perturbations, Harris sheet gets perturbed and propagating nonlinear KAWs undergoes localization and coherent structures are formed. The transverse scale size of these structures comes of the order of ion gyro radius which is consistent with the observations as well as with the results obtained from the paraxial approach based simplified model also. We have investigated the role of KAWs in the formation of current sheet/coherent structures due to the propagation of nonlinear KAWs through the Harris sheet. Based on these coherent structures, we have evaluated the power spectrum also and found that the obtained scaling after first breakpoint is quite consistent with the observation reported by Chaston et al. [Phys. Rev. Lett. 102, 015001 (2009)] in the ion diffusion region of magnetotail.