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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  06 Apr 2020

06 Apr 2020

Review status
This preprint is currently under review for the journal ANGEO.

Ducting of incoherent scatter radar waves by field-aligned irregularities

Michael T. Rietveld1,2 and Andrew Senior3 Michael T. Rietveld and Andrew Senior
  • 1EISCAT Scientific Association, Ramfjordbotn, Norway
  • 2University of Tromsø – The Arctic University of Norway, Norway
  • 3Independent Researcher, Lancaster, UK

Abstract. We provide an explanation for a mysterious phenomenon that has been recognized in recent years in EISCAT UHF incoherent scatter radar (ISR) measurement during many high power HF ionospheric pumping experiments. The phenomenon is an apparent increase in electron density observed above the HF reflection altitude, extending up to the observable limits usually in the range 400–650 km, as shown in several publications in recent years. It was shown by Senior et al. (2013) that several examples of these enhanced backscatter could not be explained by increases in electron density. A summary of characteristics of the backscatter enhancements is presented as well as the results of a survey of events. We propose that medium- to large-scale HF-induced field-aligned irregularities (tens to hundreds of m scale) act to refract the radar signals along the magnetic field, thereby acting as a guide so that the free-space r2 spreading of the signals no longer applies. The nature of the irregularities and the physical mechanism of their production by powerful HF waves is an exciting topic for future research since, surprisingly, they appear to be preferentially excited by X-mode waves. The explanation proposed here involving HF-induced irregularities may well apply to other ISR observations of the ionosphere in the presence of specific natural irregularities.

Michael T. Rietveld and Andrew Senior

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Michael T. Rietveld and Andrew Senior

Michael T. Rietveld and Andrew Senior


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