Spread-Es structure producing apparent small scale structure in the F-region

Barnes R.I. (1992) Spread-Es structure producing apparent small scale structure in the F-region. Journal of Atmospheric and Terrestrial Physics, 54 3-4: 373-389. doi:10.1016/0021-9169(92)90017-F

Author Barnes R.I.
Title Spread-Es structure producing apparent small scale structure in the F-region
Journal name Journal of Atmospheric and Terrestrial Physics
ISSN 0021-9169
Publication date 1992-01-01
Sub-type Article (original research)
DOI 10.1016/0021-9169(92)90017-F
Volume 54
Issue 3-4
Start page 373
End page 389
Total pages 17
Language eng
Subject 1902 Film, Television and Digital Media
1908 Geophysics
Abstract When transmitting on 5.8 MHz the Bribie Island HF radar array synthesizes a beam that is 2.5 wide. The beam can be steered rapidly across the sky or left to dwell in any direction to observe the fading rates of echoes within a small cone of angles. With the beam held stationary, the time scale associated with deep fading of F-region echoes is usually more than 5 min. This is consistent with the focusing and defocusing effects caused by the passage of ever-present medium-scale travelling ionospheric disturbances (TIDs). On occasion the time scale for deep fading is much shorter, of the order of tens of seconds or less, and this is thought to be due to the interference of many echoes from within the beam of the radar. It is shown that the echoes are not due to scatter from fine structure in the F-region, but rather due to the creation of multiple F-region paths with differing phase lengths by small, refracting irregularities in underlying, transparent spread sporadic-E, (Spread-Es). The natural drift of the Spread-Es causes the phase paths of the different echoes to change in different ways causing the interference. Two methods are used to investigate the rapidly fading F-region signals. Doppler sorting of the refracted F-region signal does not resolve echoes in angle of arrival suggesting that many echoes exist within a Fresnel zone [Whitehead and Monro (1975), J. atmos. terr. Phys. 37, 1427]. Statistical analysis of F-region amplitude data indicates that when the range spread in Es is severe on ionograms, then a modified Rayleigh distribution caused by the combination of 10 or so echoes is most appropriate. Using knowledge of the refracting process the scale of Es structure is deduced from these results. Both methods find a Spread-Es irregularity size of the order of 1 km or less. It is proposed that the Rayleigh type F-region signals seen by Jacobson et al. [(1991b), J. atmos. terr. Phys. 53, 63] are F-region signals refracted by spread-Es.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Unknown

Document type: Journal Article
Sub-type: Article (original research)
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