Simultaneous very high frequency and ultra high frequency observations of the aurora at Fraserburgh, Scotland

Abstract

Simultaneous three‐frequency (30, 401, and 800 Mc/s) radar studies of the aurora were made from a site in northern Scotland. A completely steerable 142‐foot‐diameter antenna was used at all frequencies, providing a 15° antenna beam at 30 Mc/s and identical scaled beams of 1.2° at 401 and 800 Mc/s. Detailed results on the position in space indicate that most echoes arise from a layerlike form of auroral scatterers whose thickness is about 10–20 km. The height distribution of the auroral return was peaked at about 100 to 120 km, but heights as great as 200 km were observed. The highest amplitude and greatest percentage of auroral echoes were found to arise from the intersection of the maximum of the visual auroral zone and the 100‐ to 120‐km orthogonality loci. Wavelength dependence and aspect sensitivity measurements at 401 and 800 Mc/s resulted in a power law dependence of λ7 and aspect sensitivity of 10 db per degree of off‐perpendicular angle. Interpretation of these results in terms of the Booker scattering formula indicates that the size of the irregularities is 45 to 90 meters along the magnetic field lines and 0.7 meter across the field lines. The wavelength dependence results from the 30‐ and 401‐Mc/s data indicate that questionable beam filling at 30 Mc/s introduces an unresolvable uncertainty of 45 db. The 30‐Mc/s aspect sensitivity results indicate an amplitude drop of 10 db per 5° of off‐perpendicular angle, or a length of the scatterers of 120 meters along the magnetic field line. Detailed comparison of magnetic activity auroral Doppler shifts and auroral echo amplitude indicates that the auroral Doppler spectrums and the amplitude of the echoes have a close relationship to the auroral current system. The auroral echoes seen at 401 Mc/s appear at times to be completely depolarized, possibly owing to Faraday rotation, but in general have a considerable degree of polarization retention. At 30 Mc/s, long‐range auroral echoes propagated by an intervening F‐layer reflection were seen as well as ground backscatter propagated by auroral sporadic E. The data indicate that the present theories for auroral scattering are insufficient to explain all the experimental characteristics observed. The plasma acoustic wave model developed for equatorial field‐aligned irregularities appears to fit most of the auroral data obtained but warrants further investigation.

On the diurnal variation of the E-region coherent HF echo occurrence

“…Presnell et al, 1959;Leadabrand et al, 1965;Unwin, 1966b;McNamara, 1972;Hanuise et al, 1991;Kustov et al, 1996;Makarevitch et al, 2002;Meyer et al, 2004;Carter and Makarevich, 2009). These studies have shown that the diurnal variations of echo occurrence at different radio frequencies/ wavelengths were quite similar.…”

“…The exact definitions have varied from study to study and have been mainly dependent on temporal and spatial resolutions of a particular radar system (e.g. Presnell et al, 1959;Leadabrand et al, 1965;Greenwald et al, 1975;Kustov et al, 1996).…”

Radar auroral echo characteristics as seen by a 398-MHz phased array radar operated at Homer, Alaska

“…of the radars that have been used, many had narrow beam w•clt!•s and short pulse widths for adequate spatial resolution; and several have had steerable beams [e.g., Leadabrand et al, 1965;Chesnut et al, 1968;Abel and Newell, 1969]. Alaska.…”

“…The auroral echo signatures typically seen during the afternoon and evening sectors are then described and discussed in relation to radar auroral echo characteristics found by previous investigations and other auroral processes. of the radars that have been used, many had narrow beam w•clt!•s and short pulse widths for adequate spatial resolution; and several have had steerable beams [e.g., Leadabrand et al, 1965;Chesnut et al, 1968;Abel and Newell, 1969]. Finally, we include a dynamic auroral echo signature that may be related to the growth phase of an auroral substorm.…”

The Millstone Hill Propagation Study

“…There are a number of quite comprehensive reviews of radio auroral work and its interpretation, for example, Booker (1960, Chamberlain (1961), Bagaryalskii (1961, Hultqvist andEgeland (1964', andLange-Hesse (1968), as well as extensive accounts of results by individual groups; for example, Leadabrand et al (1965" andChestnut et al (1968) have descr.bed the work by the Stanford B esearch institute, Unwin and Knox (iC(8) and references therein dealt with the work in New Zealand.…”