Multisite Optical Imaging of Artificial Ionospheric Plasmas

Artificial ionospheric plasmas are formed on the bottom side of the natural ionospheric F region during high-power high-frequency (HF) heating experiments and descend to altitudes as low as 140 km before disappearing. Optical emissions produced during these events often exhibit bull's-eye structures, where the artificial plasma is thought to form a central spot that diverts or blocks HF waves to form an empty ring of emissions from the natural ionosphere at higher altitudes. We present multisite image data showing that, in some cases, both the spot and ring represent distinct artificial plasma layers.