Parallel electric fields inferred during a pulsating aurora

Abstract. A sounding rocket, equipped to study pulsat-ing aurora launched from Poker Flat, Alaska on 13 March 1997 at 10:20:31 UT, measured electron precipitation over the range∼10 eV to 500 keV covering pitch-angles from 0 to 180◦. Data show electrons with energies <1 keV are mostly secondaries produced below the rocket altitude by the higher energy precipitated electrons. We observed nearly equal fluxes of up and down going electrons for energies <1 keV at altitudes from 265 to 380 km. Electron transport simulation results indicate the secondaries produced by the more ener-getic electrons will have two times higher flux in the upward direction as compared to the downward direction. Our obser-vations of nearly equal fluxes of up and downgoing electrons over a large range of altitudes is consistent with the presence of an electric potential above the rocket that reflects the upgo-ing electrons back toward the rocket where they are detected as downward going electrons. The strength of the potential is estimated to be 1.5±0.5 kV and its location is no greater than 5000 km above the rocket. Finally, the inferred potential drop exists independently of the presence of pulsations