Incoherent scatter radar observation of high frequency enhanced ion and plasma lines by X / O mode pump around critical altitude

Abstract

During an experiment involving the alternating O / X mode pump, the Incoherent Scatter Radar (ISR) observation demonstrated that the high frequency enhanced ion line (HFIL) and plasma line (HFPL) did not immediately appear, but were delayed by a few seconds after the pump onset. By examining the initial behaviors of the ion line, plasma line and electron temperature as well as ionosphere condition, it is shown that (1) the HFIL and HFPL are delayed not only in the X mode pump but also in the O mode pump; (2) the HFIL can not be observed until the electron temperature is enhanced. The analysis suggests that (1) the leakage of the X mode to the O mode pump may not be ignored; (2) the spatiotemporal uncertainty, the spatiotemporal change in the profiles of ion mass and electron density, may play an important role in the lack of the Bragg condition; (3) nevertheless, the absence of parametric decay instability can not be ruled out due to the lack of matching condition caused by the spatiotemporal uncertainty.