The Intensities of High Frequency‐Enhanced Plasma and Ion Lines During Ionospheric Heating

Abstract

AbstractAn ultrahigh frequency (UHF) observation during an ionospheric heating campaign at European Incoherent SCATter scientific association (EISCAT) demonstrates that the electron temperature and the intensities of the enhanced plasma and ion lines systematically vary as a function of the pump frequency near the fifth electron gyroharmonic. Specifically, with the change in the pump frequency, the weaker the enhancement in the electron temperature is, the more intense the intensities of the enhanced ion line is. The analysis shows that the enhanced electron temperature plays a significant role in determining the intensities of the enhanced Langmuir and ion acoustic waves by the parametric decay instability and the oscillation two‐stream instability, and the intensities of the enhanced plasma and ion lines depend on whether the enhanced Langmuir and ion acoustic waves satisfy the Bragg condition exactly or approximately. Moreover, an alternative explanation for the overshoots in the enhanced plasma and ion lines is presented, namely, the overshoots may be attributed not only to the anomalous absorption of the pump but also to the modifications of the plasma on the traveling path of the enhanced Langmuir and ion acoustic waves.