The analysis of HF-induced abnormal enhancement of plasma line

As an important characterization in ionospheric heating experiments, the disturbed plasma line have been widely studied. On November 23, 2011, a polar winter ionospheric heating experiment with the linearly varied heating frequency was carried out by China. In this experiment, a very interesting feature of HF-enhanced plasma line is observed. When the heating is on, the enhancement of plasma line is tens times larger than that of background in the first 8 minutes. Then the enhancement increases rapidly, and the increase rate can reach thousands or even tens of thousands times. Based on the comparison of the ion acoustic frequency, heating frequency and the frequency of the maximum value of plasma line, and the analysis of the matching height of parametric instability and the matching height of n times gyro-frequency, we infer that the enhanced plasma line in this experiment may be induced by parametric instability and 5 times gyro-frequency resonance.