The Super Dual Auroral Radar Network (SuperDARN) is a network of high-frequency (HF) radars located in the high-and mid-latitude regions of both hemispheres that is operated under international cooperation. The network was originally designed for monitoring the dynamics of the ionosphere and upper atmosphere in the high-latitude regions. However, over the last approximately 15 years, SuperDARN has expanded into the mid-latitude regions. With radar coverage that now extends continuously from auroral to sub-auroral and mid-latitudes, a wide variety of new scientific findings have been obtained. In this paper, the background of mid-latitude SuperDARN is presented at first. Then, the accomplishments made with mid-latitude SuperDARN radars are reviewed in five specified scientific and technical areas: convection, ionospheric irregularities, HF propagation analysis, ion-neutral interactions, and magnetohydrodynamic (MHD) waves. Finally, the present status of mid-latitude SuperDARN is updated and directions for future research are discussed.

[1] The Harang reversal is a prominent feature frequently observed in the electric and magnetic field patterns in the high-latitude auroral zone and plays an important role in substorm dynamics. A comprehensive set of instruments, including Super Dual Auroral Radar Network (SuperDARN), Defense Meteorological Satellite Program (DMSP), and Imager for Magnetopause-to-Aurora Global Exploration (IMAGE), is used to investigate the relationship between the Harang reversal and substorms. On the basis of nine events that have been analyzed, we find that the Harang reversal forms and becomes well defined during the growth phase. Azimuthal flows equatorward of the Harang reversal, a majority of which are in the subauroral region, enhance during the growth phase. The observations indicate that subauroral polarization streams (SAPS) and the Harang reversal evolve together as part of the growth phase development of the region 2 current system. Furthermore, the substorm auroral onset is seen to occur quite near the center of the Harang flow shear, which suggests that the substorm upward field-aligned current develops there. After onset, the evolution of convection flows in the vicinity of the Harang region depends strongly on their location relative to that of the onset. SAPS flows equatorward of the Harang reversal suddenly increase at the substorm onset; flow shear east of the auroral onset relaxes after the onset; and poleward flows, part of a clockwise vortex, are observed west of the auroral onset after the onset. These observations demonstrate the strong coupling between the Harang reversal evolution and substorm dynamics and suggest that the nightside region 2 physics is closely related to substorm dynamics.

Abstract.A −190-nT negative bay in the geomagnetic X component measured at Macquarie Island (−65 • ) showed that an ionospheric substorm occurred during 09:58 to 11:10 UT on 27 February 2000. Signatures of an auroral westward flow channel (AWFC) were observed nearly simultaneously in the backscatter power, LOS Doppler velocity, and Doppler spectral width measured using the Tasman International Geospace Environment Radar (TIGER), a Southern Hemisphere HF SuperDARN radar. Many of the characteristics of the AWFC were similar to those occurring during a polarisation jet (PJ), or subauroral ion drift (SAID) event, and suggest that it may have been a precursor to a fully developed, intense westward flow channel satisfying all of the criteria defining a PJ/SAID. A beamswinging analysis showed that the westward drifts (poleward electric field) associated with the flow channel were very structured in time and space, but the smoothed velocities grew to ∼800 m s −1 (47 mV m −1 ) during the 22-min substorm onset interval 09:56 to 10:18 UT. Maximum westward drifts of >1.3 km s −1 (>77 mV m −1 ) occurred during a ∼5-min velocity spike, peaking at 10:40 UT during the expansion phase. The drifts decayed rapidly to ∼300 m s −1 (18 mV m −1 ) during the 6-min recovery phase interval, 11:04 to 11:10 UT. Overall, the AWFC had a lifetime of 74 min, and was located near −65 • in the evening sector west of the Harang discontinuity. The large westward drifts were confined to a geographic zonal channel of longitudinal extent >20 • (>1.3 h magnetic local time), and latitudinal width ∼2 • . Using a half-width of ∼100 km in latitude, the peak electric potential was >7.7 kV. However, a transient velocity of >3.1 km s −1 with potential >18.4 kV was observed further poleward at the end of the recovery phase. Auroral oval boundaries determined using DMSP measurements suggestCorrespondence to: M. L. Parkinson (m.parkinson@latrobe.edu.au) the main flow channel overlapped the equatorward boundary of the diffuse auroral oval. During the ∼2-h interval following the flow channel, an ∼3 • wide band of scatter was observed drifting slowly toward the west, with speeds gradually decaying to ∼50 m s −1 (3 mV m −1 ). The scatter was observed extending past the Harang discontinuity, and had Doppler signatures characteristic of the main ionospheric trough, implicating the flow channel in the further depletion of F-region plasma. The character of this scatter was in contrast with the character of the scatter drifting toward the east at higher latitude.Key words. Ionosphere (auroral ionosphere; electric fields and currents; ionosphere-magnetospehere interactions) Magnetospheric physics (storms and substorms)

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.

Abstract. The quiet-time coherent backscatter from the Fregion observed by the Tasman International Geospace Environment Radar (TIGER) Bruny Island HF radar is analysed statistically in order to determine typical trends and controlling factors in the ionospheric echo occurrence. A comparison of the F-region peak density values from the IRI-2007 model and ionosonde measurements in the vicinity of the radar's footprint shows a very good agreement, particularly at subauroral and auroral latitudes, and model densities within the radar's footprint are used in the following analyses. The occurrence of F-region backscatter is shown to exhibit distinct diurnal, seasonal and solar cycle variations and these are compared with model trends in the F-region peak electron density and Pedersen conductance of the underlying ionosphere. The solar cycle effects in occurrence are demonstrated to be strong and more complex than a simple proportionality on a year-to-year basis. The diurnal and seasonal effects are strongly coupled to each other, with diurnal trends exhibiting a systematic gradual variation from month to month that can be explained when both electron density and conductance trends are considered. During the night, the echo occurrence is suggested to be controlled directly by the density conditions, with a direct proportionality observed between the occurrence and peak electron density. During the day, the echo occurrence appears to be controlled by both conductance and propagation conditions. It is shown that the range of echo occurrence values is smaller for larger conductances and that the electron density determines what value the echo occurrence takes in that range. These results suggest that the irregularity production rates are significantly reduced by the highly conducting E layer during the day while F-region density effects dominate during the night.