Atmospheric physics - Seeing the light

The powerful radio transmitter array at the HAARP observatory near Gakona, Alaska, is designed to transmit a narrow beam of powerful radio signals into the sky. The response to this intervention reveals details of the chemistry and physics of the ionosphere. One such experiment carried out in March 2004 had an unexpected outcome, inducing artificial optical emissions bright enough to be seen as small speckles by the naked eye. This occurred not in the quiet ionosphere, but in the midst of a pulsating aurora, and represents features much smaller and brighter than ever observed previously.