Dispersive Alfvén Waves Observed by Cluster at the Magnetopause

Abstract

We have analyzed ELF turbulence ∼0.03 - 10 Hz) observed by Cluster at the magnetopause layer during 120 multiple magnetopause crossings on a single event, December 31, 2000, 09-16 UT. Multiple crossings are produced by nonlinear, large amplitude surface waves at the magnetopause. Waves below the proton gyrofrequency fci ≈ 0.3 Hz) are identified as kinetic Alfvén waves, while waves (0.3-10 Hz) between the ion gyrofrequency and the lower hybrid frequency are consistent with short wavelength dispersive Alfvén waves with perpendicular scales less than an ion gyroradius. The Cluster observations show that the dispersive Alfvén waves at the magnetopause layer have electric field magnitudes of 5 mV/m and spectral peak power of 10-6 (V/m)2/Hz.