Abstract
Abstract. Artificial E region field aligned irregularities (FAIs) have been observed during heating experiments at the HAARP facility using a new 30 MHz coherent scatter radar imager deployed near Homer, Alaska. Irregularities were observed during brief experiments on three quiet days in July and August, 2007, when the daytime E region critical frequency was close to 3 MHz. Irregularities were consistently generated and detected during experiments with O-mode HF pumping on zenith with a 1-min on, 1-min off CW modulation. The scattering cross sections, rise, and fall times of the echoes were observed as well as their spectral properties. Results were found to be mainly in agreement with observations from other mid- and high-latitude sites with some discrepancies. Radar images of the irregularity-filled volume on one case exhibited clear variations in backscatter power and Doppler shift across the volume. The images furthermore show the emergence of a small irregularity-filled region to the south southwest of the main region in the approximate direction of magnetic zenith.
Highlights
A signature feature of ionospheric modification experiments is the production of small-scale field-aligned plasma density irregularities (FAIs) near the reflection height These irregularities give rise to coherent radar backscatter that can be detected by appropriately located low-power HF and VHF radar systems (e.g. Senior et al, 2004)
Artificial FAIs are generally believed to be generated by thermal parametric instabilities (TPIs) which form at altitudes slightly above the upper hybrid resonance height where the pump frequency is the Pythagorean sum of the plasma frequency and the electron gyrofrequency (Grach et al, 1977; Das and Fejer, 1979; Grach et al, 1981; Dsythe et al, 1982; Dsythe et al, 1983)
This paper reports on the first observations of artificial E region FAIs over the High Frequency Active Auroral Research Program (HAARP) facility with a new coherent scatter radar deployed near Homer, Alaska
Summary
A signature feature of ionospheric modification experiments is the production of small-scale field-aligned plasma density irregularities (FAIs) near the reflection height (see Robinson, 1989; Frolov et al, 1997 for reviews.) These irregularities give rise to coherent radar backscatter that can be detected by appropriately located low-power HF and VHF radar systems (e.g. Senior et al, 2004). Generating them necessitates either very low pump frequencies or, failing that, the presence of sporadic E layers or auroral precipitation. Planning experiments around these phenomena is challenging, and the latter can cause significant attenuation of the probing radar signal. Hibberd et al (1983, 1984) observed coherent backscatter from E region FAIs using the STARE radar with permanent sites in Norway and Finland suitable for supporting heater experiments at Tromsø. The recent completion of the HAARP ionospheric modification facility, which is able to radiate at frequencies as low as 2.75 MHz, prompts the reinvestigation of artificial E region FAIs and coherent radar backscatter from them. The 30 MHz radar is autonomous and remotely operable and will be available for more extensive studies in the near term
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