Phenomena in the high latitude ionosphere induced by an X-mode HF heater wave

Details Phenomena in the high latitude ionosphere induced by an X-mode HF heater wave Phenomena in the high latitude ionosphere induced by an X-mode HF heater wave

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm34a..02b&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SM34A-02

Physics

Plasma Physics

[2403] Ionosphere / Active Experiments, [2431] Ionosphere / Ionosphere/Magnetosphere Interactions, [2471] Ionosphere / Plasma Waves And Instabilities, [7839] Space Plasma Physics / Nonlinear Phenomena

Scientific paper

New experimental results are presented from high power ionospheric modification experiments with the EISCAT/Heating HF facility at Tromsø, Norway. The experiments were conducted in the course of Russian EISCAT HF heating campaigns in 2009 - 2011 using the following diagnostic tools: the EISCAT UHF incoherent scatter radar at Tromsø, the CUTLASS (SuperDARN) HF coherent radar, bi-static HF Doppler radio scatter and the EISCAT ionosonde (dynasonde). The effects on the high-latitude F region of the ionosphere by X-mode powerful HF radio waves injected towards the magnetic zenith (MZ) are analysed. We present the first experimental evidence for strong plasma modifications induced by the X-mode powerful HF radio waves. The distinctive feature of modification experiments is that the heater frequency is choosen by a special way, namely, it is above the ordinary-mode critical frequency but comparable with the extraordinary-mode critical frequency. The results show that the X-mode HF pump wave can generate very strong small-scale artificial field aligned irregularities (AFAIs) in the F-region of the high-latitude ionosphere. These irregularities, with spatial scales across the geomagnetic field of the order of 8 - 15 m, appeared 10 s - 4 min after the heater is turned on. They had the unusually long decay time which varied in a wide range between 3 and 30 min. The generation of the X-mode AFAIs was accompanied by electron temperature (Te) enhancements up to 50 % above the background level and an increase in the electron density (Ne) by up to 30 %. Such electron density enhancements can be attributed to HF-induced ionization production rather than the change of the density distribution due to the thermal diffusion. The analysis of the incoherent backscatter spectra obtained with the EISCAT UHF radar during X-mode HF pumping demonstrated the strongly enhanced ion line shoulders (upshifted and downshifted spectral peaks) observed during the whole 10 min heater-on period, which are unusual for X-mode heating. The possible mechanisms for plasma modifications induced by the X-mode powerful HF radio wave are discussed.

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