Artificial Ionospheric Layers During Pump Frequency Stepping Near The 4th Gyroharmonic At Haarp

We report on artificial descending plasma layers created in the ionosphere F region by high-power high-frequency (HF) radio waves from High-frequency Active Auroral Research Program at frequencies f(0) near the fourth electron gyroharmonic 4f(ce). The data come from concurrent measurements of the secondary escaping radiation from the HF-pumped ionosphere, also known as stimulated electromagnetic emission, reflected probing signals at f(0), and plasma line radar echoes. The artificial layers appeared only for injections along the magnetic field and f(0) > 4f(ce) at the nominal HF interaction altitude in the background ionosphere. Their average downward speed similar to 0.5 km/s holds until the terminal altitude where the local fourth gyroharmonic matches f(0). The total descent increases with the nominal offset f(0) - 4f(ce). DOI: 10.1103/PhysRevLett.110.065002