Features of Narrowband Stimulated Electromagnetic Emission Depending on the Effective Radiated Power of the EISCAT/Heating Facility

Estimates of excitation thresholds and the analysis of spectral features of narrowband stimulated electromagnetic emission (NSEE) depending on the electric-field intensity of an extraordinary polarized HF pump wave have been carried out. They are based on results obtained during power stepping EISCAT/Heating experiments. The HF pump wave was radiated toward the magnetic zenith at frequency of 5.423 MHz. The effective radiated power was changed from 55 to 360 MW. NSEE was recorded in the vicinity of St. Petersburg at a distance of ~1200 km away of the EISCAT/Heating facility. Calculations of the electric field of a powerful HF radio wave near the reflection altitude taking into account the nondeviation absorption in the underlying layers were performed. The threshold (minimum) values of the electric field required for the NSEE excitation were determined.