ON SPECTRA OF IONOSPHERIC CONDUCTIVITY VARIATIONS DURING A HEATING EXPERIMENT

Appearance of the harmonics in the spectrum of artificial emissions ge nerated during heating experiments has been reported earlier. Usually, it relates with square modulation of HF powerful wave and distortion of this time dependence due to characteristic time of electron heating /cooling. In the EISCAT-Heating experiment in November 1993, a quasi-s inusoidal modulation regime was used. Observations show the clear harm onic structure in artificial emissions in this case too. In the presen t paper we discuss a generation of harmonics of a modulation frequency due to nonlinear dependence of value of the ionosphere conductivity d isturbance from effective radiated power (ERP). A numerical model is u sed for calculations of the spectrum of the integral conductivity dist urbance variation as a function of electron density profile and ERP. F or the modulation frequency in the range of 1 - 100 Hz, the characteri stic time of electron heating/cooling was neglected, and intensity rat ios of the second and third harmonics to the fundamental frequency rea ch 0.4 and 0.15, respectively. For the modulation frequency 1375 Hz, t ime integration of the electron energy balance equation was used. The different characteristic time constants of the electron heating/coolin g at different altitudes make the behavior of the intensity ratio and phase shift of the harmonics of the integral conductivity disturbance variations more complicated. The values of the harmonic amplitude rati o in this case decrease to 0.25 and 0.1.