Aspect dependence of Langmuir parametric instability excitation observed by EISCAT

Abstract

Recent studies of X‐mode wave heating experiments observed by EISCAT (European Incoherent Scatter Scientific Association UHF radar indicate that parametric instability (PI) can be excited unexpectedly. In this paper, we reinvestigate the ionospheric heating experiment on 21 and 22 October 2012 in details. The observed HF‐enhanced ion lines (HFILs) and HF‐enhanced plasma lines (HFPLs) observed during the experiments present dependence on the heating incidence angles. The observational evidence and numerical calculation that the parallel electric field of X‐mode heating wave can exceed the PI excitation threshold at certain angles indicate the decisive role of parallel electric field for the PI excitation. The excited HFPLs and HFILs during X‐mode heating cycles also present the evidence for the non‐Maxwellian distribution of the electrons in the heated region.

GLONASS Observation of Artificial Field‐Aligned Plasma Irregularities Near Magnetic Zenith During EISCAT HF Experiment

“…This study shows the high rate GNSS data along with incoherent scatter radar can be used to study small scale density perturbation induced by HF heating. One of the recently debated topics in the ionospheric active experiment research is aspect angle‐dependent density enhancement during X mode heating at EISCAT (Blagoveshchenskaya et al., 2011a, 2011b; M. Rietveld & Senior, 2020; Senior et al., 2013; Wang & Zhou, 2017). In fact, an apparent density increase was observed through X‐mode heating in EISCAT Ne before the GLONASS passing (see 12:26 UT in Figure 2).…”

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

“…Recently, however, Wang et al (Wang X et al, 2016a(Wang X et al, , b, 2018Wang X and Zhou C, 2017) and Feng T et al (2020) claimed that some effects similar to those excited by the O mode pumping were excited by the X mode pumping at the European Incoherent Scatter Scientific Association (EISCAT) facility. Wang X et al (2016a) proposed that a small parallel component of the X mode pumping might satisfy the threshold of parametric decay instability (PDI) in an inhomogeneous plasma, and that a modified kinetic electron distribution might satisfy the PDI frequency matching condition.…”

Evidence of X-mode heating suppressing O-mode heating

“…This is because (1) X‐mode pump waves do not have a strong enough parallel electric field at the X‐mode reflection height and (2) the frequency matching condition is not satisfied at the X‐mode reflection height. It is surprising that HFPLs and HFILs resulting from X‐mode pumping have been directly observed in recent X‐mode heating experiments (Blagoveshchenskaya et al, 2014, 2015, 2017; Wang X et al, 2016a, b; Wang X and Zhou C, 2017). Optical emissions (Blagoveshchenskaya et al, 2014), artificial small‐scale FAIs (Blagoveshchenskaya et al, 2011, 2013), narrow SEEs (Blagoveshchenskaya et al, 2015, 2017), HFILs, and HFPLs (Blagoveshchenskaya et al, 2014, 2015, 2017; Wang X et al, 2016b; Wang X and Zhou C, 2017) have been observed during these recent X‐mode heating experiments.…”

“…It is surprising that HFPLs and HFILs resulting from X‐mode pumping have been directly observed in recent X‐mode heating experiments (Blagoveshchenskaya et al, 2014, 2015, 2017; Wang X et al, 2016a, b; Wang X and Zhou C, 2017). Optical emissions (Blagoveshchenskaya et al, 2014), artificial small‐scale FAIs (Blagoveshchenskaya et al, 2011, 2013), narrow SEEs (Blagoveshchenskaya et al, 2015, 2017), HFILs, and HFPLs (Blagoveshchenskaya et al, 2014, 2015, 2017; Wang X et al, 2016b; Wang X and Zhou C, 2017) have been observed during these recent X‐mode heating experiments. Vas'kov and Ryabova (1998) reported that the UH waves can also be excited by X‐mode heating through PDI near the reflection height.…”