A new radar auroral backscatter experiment
In 1982 a new radar auroral backscatter system, SABRE (Sweden and Britain Radar Experiment), commenced operation in northern Europe. Observations with this ground-based system allow estimates to be made of the electric fields in the auroral E-region. As an electric field probe, the coherent radar technique is unique in that measurements are made over a large area (∼200,000 km2) with good spatial resolution (20 × 20 km2) and with a temporal resolution of typically 20 s. The system field of view covers an L-value range 4.3–5.8. This region in the magnetosphere–ionosphere system is now accessible for the first time for detailed electric field studies. We present here observations of two pulsation events.
Field‐aligned currents associated with Pc 5 pulsations: STARE and TRIAD observations
The resonance theory for monochromatic Pc 5 micropulsations predicts that the toroidal mode resonance should be accompanied by field-aligned current systems. These currents close via Pedersen current in the ionosphere, and the drifting irregularities observed by the STARE radars are thought to be generated by the associated electric fields. Recent theoretical calculations by Walker (1980) are used to estimate the micropulsation current systems and accompanying magnetic perturbations. STARE radar observations of the pulsation electric field in the ionosphere are then compared with the corresponding magnetic perturbation observed with the TRIAD satellite magnetometer.
A note on oscillating field lines
The heuristic concept of vibrating field lines to explain micropulsation observations continues to be popular [Wilson, 1966]. It, therefore, seems appropriate to examine the equations governing this phenomenon to ascertain the mathematical reliability of such an appealing physical model. It is the contention of the author that, while there is no valid theoretical demonstration that permits the oscillation of individual field lines, there are strong theoretical reasons against such an occurrence. 
 
The basic wave equation describing low-frequency propagation in a magnetized plasma is ∂2E/∂2 = A × A × curl curl E where E is the perturbed electric field and A = B(4πρ)1/2 is the Alf ven velocity