Response of the Arecibo ionosphere to large HF-induced electron temperature enhancements

During recent experiments at Arecibo, Puerto Rico, large (1000 - >2500 K) enhancements in electron temperature have been observed when high-power radio waves reflect near the nighttime F region peak. The electron temperature enhancements are accompanied by significant (50 – 200 K) increases in ion temperature, large (10 – 25%) reductions in electron density, and strong HF-induced spread F. When large electron temperature enhancements develop, the ionosphere appears to become dynamically unstable resulting in the production of geomagnetic field-aligned striations having elevated electron temperatures and depleted electron densities. In the present work, a theoretical description of the F region thermal response is provided along with several new experimental results. An interesting aspect of this type of radio wave heating experiment is that it offers the possibility of directly measuring aeronomic parameters that are difficult to determine with other techniques.