Production of auroral zone <i>E</i> region irregularities by powerful HF heating

Hibberd, F. H.; Nielsen, E.; Stubbe, P.; Kopka, H.; Rietveld, M. T.

doi:10.1029/ja088ia08p06347

Cited by 23 publications

(17 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Beyond this, the instability process proposed by Hibberd et al [1983] to explain HF-induced E region irregularities observed with the STARE radars provides an additional mechanism for slow irregularity growth. While growth times of this order may occur when the "auxiliary processes" described above are very close to threshold, similar arguments cannot be made for the resonance instability.…”

Section: Growth and Decay Characteristicsmentioning

confidence: 91%

Observations of E region irregularities generated at auroral latitudes by a high‐power radio wave

et al. 1985

Self Cite

View full text Add to dashboard Cite

In September 1983 a series of ionospheric modification experiments was performed in Scandinavia using the high‐frequency (HF) heating facility located near Tromsø, Norway. The experiments were designed to study the production of geomagnetic field‐aligned irregularities in the auroral E region by a powerful HF radio wave. In this initial report, observations of 3.2‐m irregularities made with a mobile 46.9‐MHz field radar are presented. When ionospheric conditions are correct, irregularities having peak cross sections of about 104 m² are excited in the E region over Tromsø. The present results are consistent with theoretical studies which indicate that it is easier to generate short‐scale field‐aligned irregularities at locations where the geomagnetic dip angle is large. When the HF‐induced radar echo at 46.9 MHz is strong, the e‐folding growth times of the echo power are typically between 50 and 150 ms. However, when the E region echo over Tromsø is weak, the growth period can range from seconds to tens of seconds. The irregularities generated by the HF wave often exhibit dynamic structure both in time and in space. In general, the observations provide experimental support for instability theories that employ interactions near the upper hybrid resonance to drive the artificial irregularities. The results also indicate that naturally occurring irregularities may at times play a key role in the excitation of HF‐induced irregularities in the auroral E region. Additional processes are probably required to explain the slower irregularity growth rates often observed when radar echoes are relatively weak and occasionally observed even for relatively strong signals.

show abstract

Section: Growth and Decay Characteristicsmentioning

confidence: 91%

Observations of E region irregularities generated at auroral latitudes by a high‐power radio wave

et al. 1985

Self Cite

View full text Add to dashboard Cite

show abstract

“…AFAIs in the E region, meanwhile, can be observed with much less refraction and accompanying uncertainty in echo location. Observations of E region AFAIs at very high frequency (VHF) tend to be relatively consistent and repeatable so long as natural instabilities do not intervene (Djuth et al, ; Hibberd et al, ; Hysell & Nossa, ; Nossa et al, ). Conducting such experiments requires the ability to generate pump HF waves at frequencies below the E region critical frequency.…”

Section: Introductionmentioning

confidence: 99%

VHF Radar Images of Artificial Field‐Aligned Ionospheric Irregularities in the Subauroral E Region

2018

View full text Add to dashboard Cite

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.

show abstract

“…Moreover, the geographic constraints for field-aligned radar backscatter from E region FAIs are difficult to meet at auroral latitudes due to the low elevation angles involved and the minimal role playable by refraction, and specialized radars dedicated to heater support must generally be used. Hibberd et al (1983Hibberd et al ( , 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. In a subsequent campaign, a portable 46.9 MHz radar deployed in Sweden joined the STARE radar in conducting perhaps the most extensive study of artificial E region FAIs to date Noble, 1987).…”

Section: Subsequent Observations Of Artificially Induced Fais Werementioning

confidence: 99%

30 MHz radar observations of artificial E region field-aligned plasma irregularities

Hysell

2008

Ann. Geophys.

View full text Add to dashboard Cite

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.

show abstract

Production of auroral zone E region irregularities by powerful HF heating

Cited by 23 publications

References 13 publications

Observations of E region irregularities generated at auroral latitudes by a high‐power radio wave

Observations of E region irregularities generated at auroral latitudes by a high‐power radio wave

VHF Radar Images of Artificial Field‐Aligned Ionospheric Irregularities in the Subauroral E Region

30 MHz radar observations of artificial E region field-aligned plasma irregularities

Contact Info

Product

Resources

About