Characteristics of electromagnetic proton cyclotron waves along auroral field lines observed by FAST in regions of upward current

Abstract

Preliminary studies from FAST observations indicate that auroral ion cyclotron waves (ICWs) above the helium cyclotron frequency (ΩHe+) occur at all MLTs have amplitudes sometimes >1 V/m and often have a magnetic component even above the proton cyclotron frequency (Ωp) with amplitudes up to 2nT. Waves with transverse amplitudes greater than 100 mV/m often exhibit large spiky downward pointing field‐aligned components with amplitudes that may exceed that of transverse fluctuation. The ratio of electric to magnetic fluctuation amplitude (E1/B1) is close to c. Using the 3 dimensional electric and magnetic field measurements available from FAST it is demonstrated that these waves are in most cases polarized transverse to the ambient magnetic field (B0) and have linear polarization with wavelengths perpendicular to B0 ranging from hundreds of meters to kilometers. Calculations of the Poynting vector associated with these ICWs indicates Poynting fluxes directed downwards along B0 for waves below the local Ωp and generally upwards for waves observed close to and above this frequency with fluxes which may exceed 10% of the total field‐aligned electron beam energy flux.