The origins of mysterious &ggr; ray and radio flashes recently detected by satellite-based instruments passing over thunderstorms are examined in the context of upward propagating discharges initiated by runaway air breakdown. Preliminary calculations normalized by the recent optical measurements of so-called sprites indicate that the runaway mechanism may well be the source of these emissions. If this is true, then upward discharges represent the first known manifestation of a fundamental, new process in plasma physics. ¿ American Geophysical Union 1996