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First Observations of Recurring HF‐Enhanced Topside Ion Line Spectra Near the Fourth Gyroharmonic
Author(s) -
Rexer Theresa,
Gustavsson Björn,
Leyser Thomas,
Rietveld Michael,
Yeoman Tim,
Grydeland Tom
Publication year - 2018
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2018ja025822
Subject(s) - incoherent scatter , ionosphere , physics , spectral line , resonance (particle physics) , plasma , f region , radio wave , ultra high frequency , atomic physics , high frequency , magnetic field , zenith , geophysics , computational physics , optics , telecommunications , astronomy , quantum mechanics , computer science
We present first incoherent scatter radar observations of systematically recurring, high‐frequency (HF)‐enhanced ion line spectra at the topside F‐region ionosphere, during magnetic field aligned HF pumping in an O‐mode polarization. The European Incoherent Scatter UHF radar was directed in magnetic zenith on 9–11 March 2016 while stepping the pump frequency across the double resonance of the fourth harmonic of the electron gyrofrequency and the local upper hybrid frequency, in a 3‐min‐on, 3‐min‐off pump cycle. Topside and bottomside enhancements occur at the respective plasma resonance altitude and seem to be asymmetrically conditioned by the relative proximity of the pump frequency to the double resonance frequency. Further, the topside HF‐induced ion line enhancements predominantly appear while the pump frequency is just below the double resonance frequency and only simultaneous to strong bottomside enhancements. A powerful, HF radio wave in O‐mode, transmitted in the direction of magnetic zenith is reflected a few kilometers below the plasma resonance altitude, where the pump frequency is equal to the local plasma frequency, on the bottomside F‐region in the ionosphere. Transionospheric propagation of the pump wave outside the radio window can be facilitated by density striations in the plasma, and we consider, in detail, the possible mechanisms proposed for propagation outside the standard radio window.