Comment on "Parametric Instability Induced by X-Mode Wave Heating at EISCAT" by Wang et al. (2016)

• Published in: Journal of Geophysical Research: Space Physics
• Main Authors: Blagoveshchenskaya, N. F., Borisova, T. D., Yeoman, T. K.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union (AGU), Wiley 2018
• Subjects: ionospheric modification; powerful HF radio waves; Arctic; Antarctic; Norway; Antarc*; Arctic and Antarctic Research Institute; EISCAT
• Online Access: http://onlinelibrary.wiley.com/doi/10.1002/2017JA023880/abstract; http://hdl.handle.net/2381/40879; https://doi.org/10.1002/2017JA023880

The data used in this comment are available through the EISCAT Madrigal database (http://www.eiscat.se/madrigal/). Publisher's version/PDF may be used 6 months after publication In their recent article Wang et al. (2016) analyzed observations from EISCAT (European Incoherent Scatter) Scientific Association Russian X-mode heating experiments and claimed to explain the potential mechanisms for the parametric decay instability (PDI) and oscillating two-stream instability (OTSI). Wang et al. (2016) claim that they cannot separate the HF-enhanced plasma and ion lines excited by O or X mode in the EISCAT UHF radar spectra. Because of this they distinguished the parametric instability excited by O-/X-mode heating waves according to their different excitation heights. Their reflection heights were determined from ionosonde records, which provide a rough measure of excitation altitudes and cannot be used for the separation of the O- and X-mode effects. The serious limitation in their analysis is the use of a 30 s integration time of the UHF radar data. There are also serious disagreements between their analysis and the real observational facts. The fact is that it is the radical difference in the behavior of the X- and O-mode plasma and ion line spectra derived with a 5 s resolution, which provides the correct separation of the X- and O-mode effects. It is not discussed and explained how the parallel component of the electric field under X-mode heating is generated. Apart from the leakage to the O mode, results by Wang et al. (2016) do not explain the potential mechanisms for PDI and OTSI and add nothing to understanding the physical factors accounting for the parametric instability generated by an X-mode HF pump wave. EISCAT is an international scientific association supported by research organizations in China (CRIRP), Finland (SA), Japan (NIPR and STEL), Norway (NFR), Sweden (VR), and the United Kingdom (NERC). N.B. and T.B. are supported by Arctic and Antarctic Research Institute. T.K.Y. is supported by Science and Technology Facilities Council grant ST/H002480/1. Peer-reviewed Publisher Version