On the occurrence and motion of decametre-scale irregularities in the sub-auroral, auroral, and polar cap ionosphere

Abstract

Abstract.The statistical occurrence of decametrescale ionospheric irregularities, average line-of-sight (LOS) Doppler velocity, and Doppler spectral width in the subauroral, auroral, and polar cap ionosphere (−57 • to −88 • ) has been investigated using echoes recorded with the Tasman International Geospace Environment Radar (TIGER), a SuperDARN radar located on Bruny Island, Tasmania (147.2 • E, 43.4 • S geographic; −54.6 • ). Results are shown for routine soundings made on the magnetic meridian beam 4 and the near zonal beam 15 during the sunspot maximum interval December 1999 to November 2000. Most echoes were observed in the nightside ionosphere, typically via 1.5-hop propagation near dusk and then via 0.5-hop propagation during pre-midnight to dawn. Peak occurrence rates on beam 4 were often > 60% near magnetic midnight and ∼−70 • . They increased and shifted equatorward and toward pre-midnight with increasing K p (i.e. B z southward). The occurrence rates remained very high for K p > 4, despite enhanced D-region absorption due to particle precipitation. Average occurrence rates on beam 4 exhibited a relatively weak seasonal variation, consistent with known longitudinal variations in auroral zone magnetic activity (Basu, 1975). The average echo power was greatest between 23 and 07 MLT. Two populations of echoes were identified on both beams, those with low spectral width and a mode value of ∼9 m s −1 (bin size of 2 m s −1 ) concentrated in the auroral and sub-auroral ionosphere (population A), and those with high spectral width and a mode value of ∼70 m s −1 concentrated in the polar cap ionosphere (population B). The occurrence of population A echoes maximised post-midnight because of TIGER's lower latitude, but the subset of the population A echoes observed near dusk had characteristics reminiscent of "dusk scatter" (Ruohoniemi et al., 1988). There was a dusk "bite out" of large spectral widths between ∼15 and 21 MLT and poleward of −67 • , and a predawn enhancement of large spectral widths between ∼03 andCorrespondence to: M. L. Parkinson (m.parkinson@latrobe.edu.au) 07 MLT, centred on ∼−61 • . The average LOS Doppler velocities revealed that frequent westward jets of plasma flow occurred equatorward of, but overlapping, the diffuse auroral oval in the pre-midnight sector.

Climatology of GPS phase scintillation and HF radar backscatter for the high-latitude ionosphere under solar minimum conditions

“…It should be noted that the HF backscatter occurrence at high latitudes is strongly dependent on HF radio wave propagation in addition to the presence of ionospheric irregularities themselves (Milan et al, 1997;Parkinson et al, 2003). Solar illumination controls the E-and F-region electron density and the HF propagation modes.…”

HF radar observations of ionospheric backscatter during geomagnetically quiet periods

“…The importance of large-scale irregularities for generation of decameter-scale waves has been noted in some previous studies (Jayachandran et al, 2000;Parkinson et al, 2003), although experimental evidence was difficult to obtain. Similarly, Milan and Lester (1999) and Danskin et al (2002) have conducted quantitative assessments of the role of the E-region conductance in the power of coherent echoes from the F-region, but results were inconclusive, as often the effect was masked by variations in other parameters such as electric field and electron density.…”

“…Several previous studies employed HF radar data on the echo occurrence and/or power in attempt to quantify this effect using coincident density measurements with ionosondes (Milan et al, 1997) and ISR systems (Milan and Lester, 1999;Danskin et al, 2002) or other considerations of the expected dependencies (Ruohoniemi and Greenwald, 1997;Ballatore et al, 2000;Parkinson et al, 2003;Koustov et al, 2004). In this context, using HF radars of the Super Dual Auroral Radar Network (SuperDARN) offers excellent opportunities to further advance our understanding of factors that control generation and detection of decameter-scale waves in the Fregion.…”

“…Ruohoniemi and Greenwald, 1997;Milan et al, 1997;Ballatore et al, 2000;Parkinson et al, 2003;Koustov et al, 2004;Wild and Grocott, 2008;Kane and Makarevich, 2010;Kumar et al, 2011). These studies have typically focused on a particular subset of effects, which resulted in a number of other effects remaining coupled.…”

An auroral westward flow channel (AWFC) and its relationship to field-aligned current, ring current, and plasmapause location determined using multiple spacecraft observations

“…Qualitatively, the observations reveal a "jet-like" AWFC . AWFCs and PJ/SAIDs have peak occurrence in the premidnight sector (Karlsson et al, 1998), and HF radars have preferred range windows for detecting ionospheric scatter determined by the magnetic field geometry and prevailing propagation conditions (Parkinson et al, 2003b). The radar operating frequency was fixed within the band 11 400-11 650 kHz for the duration of the experiment.…”