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,

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The Johns Hopkins University/Applied Physics Laboratory HF radar at Goose Bay often sees F‐region drifts or electric fields which are associated with field line resonances in the Earth's magnetosphere. These resonances are seen in the interval from local midnight to morning, and have discrete, latitude‐dependent frequencies at approximately 1.3, 1.9, 2.6–2.7, and 3.2–3.4 mHz. We show that these frequencies are compatible with MHD waveguide modes, with antisunward propagation and reflection at the magnetopause and at turning points on dipolar field lines.

The Stare (Scandinavian twin auroral radar experiment) auroral radar system has been used to measure ionospheric electric fields associated with Pc 5 geomagnetic pulsations. With this system, electric fields are derived from the drift velocity of radar auroral irregularities. The spatial resolution is 20 km over a 200,000‐km² grid, and the temporal resolution is 20 s. It has been found that the oscillating electric field associated with a hydromagnetic field line resonance produces poleward moving, bandlike regions of radar aurora, which are aligned in the east‐west direction. The drift of the irregularities within these bands is alternately eastward and westward. The Stare electric field data have been used in conjunction with the Biot‐Savart Law and an assumed height‐integrated conductivity of 8–10 Ω−1 to calculate the ground magnetic disturbance. It has been found that the H and Z are well predicted, whereas D is generally underestimated. These results are consistent with a 90° rotation of the magnetic polarization ellipse in the ionosphere. By Fourier analyses of the Stare data it is found that the half‐power latitudinal width of the field line resonance is typically 100 km in the ionosphere. Moreover, the north‐south electric field undergoes a 180° phase shift about the resonance as predicted by theory. The data have been used to estimate equatorial plasma densities for 6 < L < 7, and values of the order of 20 cm−3 have been obtained. However, these determinations are strongly affected by distortions of the geomagnetic field from a dipolar geometry. In summary, (1) the experimental results strongly support the hydromagnetic field line resonance theory of pulsations; (2) the magnetic polarization ellipse is indeed rotated through 90° by the ionosphere; (3) the phenomena previously observed by auroral radar workers in association with Pc 5 pulsations were related to the electric field of the hydromagnetic wave near resonance; and (4) auroral radar measurements can be used to estimate the equatorial magnetospheric plasma density in the region 5 < L < 8.

A detailed analysis of HF radar data of a ULF pulsation event in the postmidnight sector on January 11, 1989, has been carried out using techniques which allow the instantaneous amplitude and phase to be determined as functions of geomagnetic latitude, longitude, and time. Field line resonances with several different frequencies occur simultaneously at different latitudes. These can be associated with cavity mode frequencies of 1.3 mHz, 1.9 mHz, 2.7 mHz, and 3.3 mHz. In addition there is a resonance at 0.8 mHz which does not fit well with a cavity picture. These frequencies are constant to better than 10% over a local time period of nearly 4 hours. They show a packet structure as would be expected if they were triggered by a succession of impulses. The phase changes arbitrarily from packet to packet, but the frequency remains constant. The position of the maximum of the resonance as a function of time changes systematically. It is shown that this arises as the length of the field line changes with time; the resonance remains on the field line having appropriate length and Alfvén speed. The field‐aligned currents driven by the resonances can be as large as 5 μA m−2 at ionospheric heights. The data support a picture of modes driven by solar wind impulses. It may be more appropriate to speak of a waveguide rather than a cavity with the phase velocity of the mode matching the velocity of the impulse along the magnetopause. A difficulty associated with this picture is that the great reproducibility of the frequencies is not consistent with the variability of the magnetopause, which forms one of the boundaries of the assumed resonator. It is, however, difficult to conceive of other resonators, for example in the magnetotail, which would provide a better explanation of the observations.