地球磁层顶的漂移动力学Alfvn波不稳定性及其反常输运效应

UNSTABLE DRIFT KINETIC ALFVEN MODEL AT THE MAGNETOPAUSE

本文用回旋动力学研究了磁层顶等离子体低频漂移动力学不稳定性.在β≥1附近发现两支不稳定的漂移动力学Alfvèn模(DKA).它们可在▽T(∥-▽n)(?)0时激发,速度剪切提供主要的自由能源.两支DKA均具有非零的(δE_y,δE_∥)和(δB_x,δB_∥).在湍动的非线性饱和状态下,δB_x的起伏可导致很强的反常输运,当|δB_x|=1nT时,D_⊥可达到10~9m^2/s的数量级.因此,DKA可能在太阳风-磁层耦合过程中起重要作用.

Low frequency drift kinetic instabilities at the magnetopause are investigated by using the gyrokinetic formalism- Two unstable branches of drift kinetic Alfven modes, A and B, may appear in the case of plasma (3^1, which are shown to be related with inhomogenities of ions and electrons, respectively. The velocity shear provides an important free energy source. The presence of the temperature gradient anti-parallel to the density gradient is necessary for exciting the instabilities. It is found that for both A and B modes the magnetic field has perturbations in the direction normal to the magnetopause. Once the amplitude of waves grows and the perturbation becomes turbulent, magnetic migration may take place, leading to substantial anomalous transport across the magnetopause. Quasilinear anomalous diffusivity is calculated and shown to be in the order of 109m2/s even if |δBx|≈1nT. Thus, the drift Kinetic Alfven mode can be considered to be responsible for most of the anomalous transport phenomena in the case of northward IMF.