VHF Radar Images of Artificial Field‐Aligned Ionospheric Irregularities in the Subauroral E Region. Issue 3 (25th March 2018) - Hysell, D. L.
Abstract: Artificial E region field‐aligned plasma density irregularities (AFAIs) have been generated using the High‐frequency Active Auroral Research Program (HAARP) ionospheric modification facility in Gakona and observed with a 30 MHz coherent scatter radar imager in Homer, Alaska. The AFAIs were generated using a distinctive, twisted‐beam antenna pattern that illuminated a particularly broad volume overhead. The broad beam facilitates studies of natural sporadic E layer patches when they are present. The center of the pattern was pointed at different angles between zenith and magnetic zenith to examine the effects on the AFAI morphology. Radar images of AFAIs generally resemble the radiation pattern of the high‐frequency source, but the irregularities are strongest within a narrow range of zenith angles bounded approximately by the Spitze angle. A number of factors which might influence AFAI generation and detection are examined. The most important is most likely the requirement for the pump mode to have a standing‐wave component for thermal parametric instability to operate. Key Points: Radar images of E region AFAIs generated over HAARP using its twisted‐beam mode are presented The spatial distribution of the backscatter is similar but not identical to the HF radiation pattern The most important difference is due to preference for irregularities generated within the Spitze