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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 1
Ann. Geophys., 36, 243-251, 2018
https://doi.org/10.5194/angeo-36-243-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Ann. Geophys., 36, 243-251, 2018
https://doi.org/10.5194/angeo-36-243-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 21 Feb 2018

Regular paper | 21 Feb 2018

Evidence of L-mode electromagnetic wave pumping of ionospheric plasma near geomagnetic zenith

Thomas B. Leyser1, H. Gordon James2, Björn Gustavsson3, and Michael T. Rietveld4 Thomas B. Leyser et al.
  • 1Swedish Institute of Space Physics, Uppsala, Sweden
  • 2Department of Physics and Astronomy, University of Calgary, Calgary, Canada
  • 3Department of Physics and Technology, UiT The Arctic University of Norway, Tromsø, Norway
  • 4EISCAT Scientific Association, Ramfjordmoen, Norway

Abstract. The response of ionospheric plasma to pumping by powerful HF (high frequency) electromagnetic waves transmitted from the ground into the ionosphere is the strongest in the direction of geomagnetic zenith. We present experimental results from transmitting a left-handed circularly polarized HF beam from the EISCAT (European Incoherent SCATter association) Heating facility in magnetic zenith. The CASSIOPE (CAScade, Smallsat and IOnospheric Polar Explorer) spacecraft in the topside ionosphere above the F-region density peak detected transionospheric pump radiation, although the pump frequency was below the maximum ionospheric plasma frequency. The pump wave is deduced to arrive at CASSIOPE through L-mode propagation and associated double (O to Z, Z to O) conversion in pump-induced radio windows. L-mode propagation allows the pump wave to reach higher plasma densities and higher ionospheric altitudes than O-mode propagation so that a pump wave in the L-mode can facilitate excitation of upper hybrid phenomena localized in density depletions in a larger altitude range. L-mode propagation is therefore suggested to be important in explaining the magnetic zenith effect.

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Transmission of powerful radio waves into the overhead ionosphere is used to study plasma turbulence processes. It is well known that the ionospheric response to radio waves is the strongest in the direction of the geomagnetic field. We have found evidence that the transmitted radio wave can propagate in a mode that enables the wave to propagate much higher in altitude and deeper into the ionosphere than what is usually expected, which may account for the strong plasma response observed.
Transmission of powerful radio waves into the overhead ionosphere is used to study plasma...
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