Artificial small-scale field-aligned irregularities in the high latitude F region of the ionosphere induced by an X-mode HF heater wave

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. The experiments were conducted using the EISCAT/Heating facility and UHF radar at Tromsø, Norway, the CUTLASS (SuperDARN) radar and the EISCAT ionosonde (dynasonde). The results show that the X‐mode HF pump wave, radiated into the magnetic zenith from the HF heater, 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, are generated when the heater frequency is above the ordinary‐mode critical frequency but comparable with the extraordinary‐mode critical frequency. 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%.