A mechanism for extraordinary bright radiowave-induced aurora in the ionospheric E region

We will show that the presence of height-extended ionization in the night-time ionospheric E region during high-power radiowave transmission into the magnetic zenith could allow for strong self-focusing of the transmitter beam due to the resonance instability near the upper-hybrid resonance level (the so-called magnetic zenith effect, never before reported for the E region) and for unusually strong enhancement in effective radiowave power due to the parametric instability, occurring in the Langmuir resonance region. This leads to 36-40 times higher effective radiated power and 36-40 times brighter optical emissions as was observed during the extraordinary bright (4 kR) radiowave-induced 557.7-nm aurora event.