A new extreme ultraviolet (EUV) emission in the 170- to 400-¿ spectral range has been regularly observed at night when looking down over the magnetic dip equator from an earth orbiting satellite at 750-km altitude. The radiation is believed to be &lgr;?304 ¿ recombination emission from energetic helium ions and appears as a single arc, quite distinct in spatial form from the oxygen emission arcs. The magnitude of the EUV emission correlates with indices of geomagnetic activity, indicating that precipitating particles are the energy source. A mechanism is proposed in which alpha particles scatter downward from the ring current repeatedly recombine and strip as they enter the atmosphere and lose energy. As a result, numerous excited atomic states are created, and EUV emissions is produced. A computer-coded model of this process using Monte Carlo techniques has been developed. Comparison of the observations with models has yielded information on the altitude and scale height of the emitting region.