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first_imgPc3–4 magnetic pulsations have been observed at Halley, Antarctica (L = 4.2), simultaneously with oscillations in the phase of F-region echoes received using a digital ionosonde. One event, lasting more than 6 hours in the afternoon of 15 December 1982, shows a crossing of the plasmapause as Halley moved into the bulge region of the plasmasphere. On the ionosonde it is marked by a change in frequency of the Pc3–4 oscillations and a short lived or sharply bounded charged particle precipitation event. On the magnetometer it can be deduced from the changes in ellipticity of pulsations occurring simultaneously at three separate frequencies. The amplitude of the ionosonde phase pulsations is shown to peak when the field line with that natural resonant frequency passes through the observation site. Cross spectral analysis techniques have been used on this event to investigate the relationships between the magnetic field components and ionospheric echo parameters, and the physical processes linking the two. The phase difference between the magnetometer and ionosonde pulsations is highly variable. Detailed analysis supports a combination of direct compressional action by the hydromagnetic wave and vertical motion induced by an E × B drift.last_img read more

first_imgWhen conducting marine seismic surveys, ocean currents noticeably perturb seismic streamers from their desired location. To accurately monitor a reservoir, the receivers in the streamers must be as close as possible to their previous positions. Therefore, it is desirable to know the currents in real time. Previous work has used the position and tension in a streamer to infer the currents. However, in many streamer systems, tension is not measured along the streamer. To overcome this problem, we propose that, by assuming that ocean currents are horizontally divergence-free, it should still be possible to reconstruct the currents from the positions of multiple streamers. Additionally, the previous work assumed that, when modelling a streamer, bending stiffness can be neglected. It is not clear that this assumption is correct when steering devices are attached; we therefore examine this assumption, using a novel finite difference scheme that incorporates bending stiffness, and conclude that it is safe to do so. Should such a method for inferring currents be implemented, the resulting information should not only be of value to the seismic industry, but also of use to oceanographers who wish to study submesoscale processeslast_img read more