FAST observations of inertial Alfven waves in the dayside aurora

Bursts of large amplitude impulsive electric and magnetic field oscillation s are a common feature observed from FAST when crossing the dayside auroral oval at altitudes from 1500-2500 km. The oscillations have transverse ampl itudes of up to 1 Vim and 100nT and exhibit a parallel electric field compo nent with amplitudes which may be as large as 100mV/m. Calculation of E-1/B -1 over 100 events yields an average value four times the local Alfven spee d. The wave period is usually less than 0.25s with 'perpendicular wavelengt hs' which average to 7.1 electron skin depths (c/omega(pe)similar to 80m). Poynting flux calculations indicate predominately downward fluxes with magn itude up 10(-2) Wm(-2) usually accompanied by a smaller upwards component. Invariably these waves are accompanied by field-aligned fluxes of down goin g and sometimes counterstreaming suprathermal electrons. Comparison with th eoretical studies indicate that these observations are consistent with the characteristics of a shear Alfven wave with k(perpendicular to)omega(pc)/c propagating in the inertial dispersive regime and interfering with a reflec ted component. However the observed large parallel electric field component , if real, has yet to be explained.