Abstract
Abstract. High-frequency electromagnetic pumping of ionospheric F-region plasma at high and mid latitudes gives the strongest plasma response in magnetic zenith, antiparallel to the geomagnetic field in the Northern Hemisphere. This has been observed in optical emissions from the pumped plasma turbulence, electron temperature enhancements, filamentary magnetic field-aligned plasma density irregularities, and in self-focusing of the pump beam in magnetic zenith. We present results of EISCAT (European Incoherent SCATter association) Heating-induced magnetic-zenith effects observed with the EISCAT UHF incoherent scatter radar. With heating transmitting a left-handed circularly polarized pump beam towards magnetic zenith, the UHF radar was scanned in elevation in steps of 1.0 and 1.5∘ around magnetic zenith. The electron energy equation was integrated to model the electron temperature and associated electron heating rate and optimized to fit the plasma parameter values measured with the radar. The experimental and modelling results are consistent with pump wave propagation in the L mode in magnetic zenith, rather than in the O mode.
Highlights
A powerful high-frequency (HF) electromagnetic wave transmitted from the ground into the ionospheric F region stimulates the strongest plasma response on long timescales in the direction antiparallel to the geomagnetic field in the Northern Hemisphere as seen from the HF transmitter
We have presented experimental and modelling results concerning electron heating and the ionospheric plasma response to HF pumping near magnetic zenith
The EISCAT Heating facility was used to pump ionospheric F-region plasma by cycling 150 s on–85 s off with an LHCP HF beam directed in magnetic zenith
Summary
A powerful high-frequency (HF) electromagnetic wave transmitted from the ground into the ionospheric F region stimulates the strongest plasma response on long timescales in the direction antiparallel to the geomagnetic field in the Northern Hemisphere as seen from the HF transmitter. This magnetic zenith effect has been observed in several ways for a range of pump frequencies in experiments at high and mid latitudes. Kosch et al (2000) observed that while the HF beam was directed vertically, the region of maximum optical emissions was displaced towards magnetic zenith as seen from EISCAT Heating. The authors noted that published data of coherent HF radar scatter off geomagnetic field-aligned density irregularities tend to maximize in the magnetic field-aligned direction
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