STIMULATED EMISSIONS AROUND 2ND-HARMONIC OF TROMSO HEATER FREQUENCY OBSERVED BY LONG-DISTANCE DIAGNOSTIC HF TOOLS

Observations of stimulated electromagnetic emission (SEE) around the s econd harmonic of Tromso heater frequency carried out by long-distance diagnostic HF tools are presented. Diagnostic tools are located at a distance of 1200 km from the Tromso HF heater. Observed SEE spectra sh ow: (1) spectral broadening up to 30 kHz; (2) frequency shift of the m aximum amplitude in the SEE spectra from the heater second harmonic fr equency 8080 kHz by 16-20 kHz; (a) dependence of the maximum amplitude on the heater power level. The detected features in the SEE spectra h ave not been observed before in ionospheric heating experiments and ma y be the second harmonic of the downshifted maximum. The strongest can didate is the coalescense (head-on collisions) of Langmuir waves produ ced in the heated volume.