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There may be a simple explanation for the puzzling auroral flashes seen by astronaut Ed Lu (Nature 425, 888; 2003). They could be due to an electrical discharge between regions of the atmosphere containing different electrostatic charges.

The fact that the flashes were visible only in the direction of the aurora suggests that the charged particles in the aurora are important. It is well known that ionizing radiation can trigger an avalanche breakdown of an insulating gas; this is, in fact, one of the ways of detecting ionizing radiation, as in a Geiger counter. The resulting burst of energy will release the built-up charge, and create a flash of light in the process. Some explanation for the initial build-up of charge is also needed, and could arise from the frictional forces of the high-speed winds in the upper atmosphere.