Letter to the Editor

Anisotropic and mass-dependent energization of heavy ions by kinetic Alfvén waves

¹ Purple Mountain Observatory, 2 West Beijing Road, Nanjing 210008, PR China e-mail: djwu@pmo.ac.cn
² Graduate School of Chinese Academy of Sciences, Beijing 100039, PR China

Received: 13 March 2006
Accepted: 13 April 2006

Abstract

Context.Some recent observations of the solar corona suggest that the heavy ions undergo an anisotropic (mainly across the magnetic field) and mass-dependent energization.

Aims.In this work, we investigate the nonlinear interaction of heavy ions with kinetic Alfvén waves, in particular, their energization in the nonlinear kinetic Alfvén waves.

Methods.Based on a three-component plasma model including electrons, protons, and heavy ions, a localized nonlinear structure of kinetic Alfvén wave is presented. In the nonlinear wave, the heavy ions are energized in the cross-field and field-aligned by the perpendicular polarization and the parallel acceleration of the wave electric field.

Results.It is found that the ion cross-field energization depends on its mass and abundance in the same way that the velocity is proportional to the mass-charge ratio and decreases with the abundance ratio. On the other hand, the ion field-aligned energy is proportional to the charge, but is free of the mass and abundance. In the low abundance case (<10%), in particular, the minor heavy ions have strongly anisotropic temperature as well as are hotter and flow faster than protons. The resulting ion-proton temperature ratio is proportional to the mass number and the square of the mass-charge ratio, and the ion perpendicular-parallel temperature ratio is proportional to the cube of the mass-charge ratio.

Conclusions.This anisotropic and mass-dependent energization mechanism by kinetic Alfvén waves for ions can be potentially important for understanding the microphysics of the energization of minor heavy ions observed in the solar corona.