The Super Dual Auroral Radar Network (SuperDARN) has been operating as an international co-operative organization for over 10 years. The network has now grown so that the fields of view of its 18 radars cover the majority of the northern and southern hemisphere polar ionospheres. SuperDARN has been successful in addressing a wide range of scientific questions concerning processes in the magnetosphere, ionosphere,

[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.

The retarding potential analyzer aboard Ogo 6 has provided high-resolution observations of the ion concentration along the satellite path. Changes in ion concentration as small as 0.03% and at times as small as 0.01% could be measured. Spatial resolution varied from 35 to 380 m. Samples of data have been analyzed to determine the spectral properties of the F region irregularities observed. The most common frequency spectrum observed follows to a very good approximation a power law of the form Aaf-'•aS '•, where ,4 is the irregularity amplitude, fis the observed frequency, and S is the irregularity scale size. The spectrum was measured over the scale size range 70 m to 7 km, and the values of n obtained were close to 1, the average value being 0.95. The spectral index n is found to be insensitive to irregularity amplitude. This type of spectrum suggests that the irregularities in this scale size range result from the turbulent dissipation of larger irregularities. At the equator the larger irregularities are probably produced by convective electric fields. At high latitudes, electric fields may also be involved, but other factors such as precipitating particles may contribute to, or be primarily responsible for, the production of large irregularities. Examples of other types of spectra associated with wavelike irregularities and with 'ground glass' (high-frequency noise) irregularities are also shown. 1497

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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. Seasonal and diurnal variations in the direction of propagation of medium-scale travelling ionospheric disturbances (MSTIDs) have been investigated by analyzing sea echo returns detected by the TIGER SuperDARN radar located in Tasmania (43.4 • S, 147.2 • E geographic; −54.6 • ). A strong dependency on local time was found, as well as significant seasonal variations. Generally, the propagation direction has a northward (i.e. equatorward) component. In the early morning hours the direction of propagation is quite variable throughout the year. It then becomes predominantly northwest and changes to northeast around 09:00 LT. In late fall and winter it changes back to north/northwest around 15:00 LT. During the other seasons, northward propagation is very obvious near dawn and dusk, but no significant northward propagation is observed at noon.It is suggested that the variable propagation direction in the morning is related to irregular magnetic disturbances that occur at this local time. The changes in the MSTID propagation directions near dawn and dusk are generally consistent with changes in ionospheric electric fields occurring at these times and is consistent with dayside MSTIDs being generated by the Lorentz force.

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Abstract. The dual HF radars comprising the Tasman International Geophysical Environment Radar (TIGER) system often observe localized high-velocity F-region plasma flows (≥1500 m/s) in the midnight sector (20:00–02:00 MLT) at magnetic latitudes as low as Λ=60° S. The flow channels exhibit large variability in the latitudinal extent and electric field strength, and are similar to the subauroral polarization stream or SAPS, a plasma convection feature thought to be related to the polarization electric field due to the charge separation during substorm and storm development. In this study, the 2-D plasma drift velocity within the channel is derived for each of the two TIGER radars from the maximum velocities measured in all 16 radar beams within the latitudinally narrow channel, and the time variation of the subauroral electric field is examined near substorm onset. It is demonstrated that the flow channel often does not have a clear onset, rather it manifests differently in different phases of its evolution and can persist for at least two substorm cycles. During the growth phase the electric fields within the flow channel are difficult to distinguish from those of the background auroral convection but they start to increase near substorm onset and peak during the recovery phase, in contrast to what has been reported previously for auroral convection which peaks just before the substorm onset and falls sharply at the substorm onset. The response times to substorm onset range from −5 to +40 min and show some dependence on the substorm location with longer delays observed for substorms eastward of the radars' viewing area. The propagation velocity of the high-velocity region is also investigated by comparing the observations from the two closely-spaced TIGER radars. The observations are consistent with the notion that the polarization electric field is established with the energetic ions drifting westward and equatorward from the initial substorm injection. The ion injection front can precede that of the electrons and hence substorm onset resulting in a negative response time of a few minutes.