On the dissipation scale of broadband ELF waves in the auroral region

摘要

1 Whereas turbulent cascades of Alfven waves in the solar wind typically damp atwavelengths near the ion inertial length, in the auroral acceleration region many observershave reported Alfven waves at the much smaller scales of the electron inertial length andthe ion gyroradius. Using a technique based on a continuous wavelet transform, weinvestigate a few examples from FAST data of broadband turbulence, which is typicallyattributed to Doppler shift of small-scale Alfven waves from low frequencies to much higherfrequencies in the spacecraft frame. We find that in some cases the dissipation scale is at theion gyroradius while in other cases the waves damp at the electron inertial length. Wealso show evidence for wave damping at plasma frame frequencies of 1 Hz, which may berelated to the influence of the ionospheric Alfven resonator. We discuss the implications ofour results for particle energization in the auroral acceleration region, as well as strengthsand limitations of the technique