The analysis of double-peaked spectrum in the enhanced plasma lines

The polar winter ionospheric heating experiments with the heating frequency linearly varied are carried out on November 23, 2011 at Tromso, Norway. The heating waves were O-mode polarization. A double-peaked spectrum is present in the enhanced plasma lines which observed with UHF incoherent radar, and the two peaks are at different frequencies. The enhanced structure is present throughout all the heating time, and the enhancement could reach several tens of thousands times larger than that of background. By the analysis of UHF radar data and the theory which could affect the plasma lines structure, the enhanced plasma spectrum in this paper may be caused by suprathermal electrons. With the incidence of powerful HF waves on ionosphere, the ambient electrons around reflection height are accelerated, and some of them become suprathermal electrons. Then the electron speed distribution function is changed, hence the double-peaked spectrum is formed.