Intermediate downshifted maximum of stimulated electromagnetic emission at high-power HF heating: A new twist on an old problem

摘要

We report a new spectral feature of Stimulated Electromagnetic Emission (SEE) from the F region ionosphere observed during high-power HF heating experiments at the SURA and High Frequency Active Auroral Research Program heating facilities. It is located in the SEE spectrum between the pump wave frequency f_0 and the well-known Downshifted Maximum and thus named the Intermediate Downshifted Maximum (IDM). IDM appears at effective radiated powers (ERP) P_0 ?30 MW and the pump frequencies above electron gyroharmonics, f_0 ?sf_(ce) ? 50 (up to 250) kHz (s= 2, 3, 4). It mirrors the well-known Upshifted Maximum (UM) relative to f_0. The salient stationary and dynamic properties of IDM are described and discussed.