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High-latitude observations of impulse-driven ULF pulsations in the ionosphere and on the ground

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journal contribution
posted on 10.03.2017, 16:14 by F. W. Menk, T. K. Yeoman, D. M. Wright, M. Lester, F. Honary
We report the simultaneous observation of 1.6–1.7 mHz pulsations in the ionospheric F-region with the CUTLASS bistatic HF radar and an HF Doppler sounder, on the ground with the IMAGE and SAMNET magnetometer arrays, and in the upstream solar wind. CUTLASS was at the time being operated in a special mode optimized for high resolution studies of ULF waves. A novel use is made of the ground returns to detect the ionospheric signature of ULF waves. The pulsations were initiated by a strong, sharp decrease in solar wind dynamic pressure near 09:28 UT on 23 February 1996, and persisted for some hours. They were observed with the magnetometers over 20° in latitude, coupling to a field line resonance near 72° magnetic latitude. The magnetic pulsations had azimuthal m numbers ~ -2, consistent with propagation away from the noon sector. The radars show transient high velocity flows in the cusp and auroral zones, poleward of the field line resonance, and small amplitude 1.6–1.7 mHz F-region oscillations across widely spaced regions at lower latitudes. The latter were detected in the radar ground scatter returns and also with the vertical incidence Doppler sounder. Their amplitude is of the order of ± 10 ms-1. A similar perturbation frequency was present in the solar wind pressure recorded by the WIND spacecraft. The initial solar wind pressure decrease was also associated with a decrease in cosmic noise absorption on an imaging riometer near 66° magnetic latitude. The observations suggest that perturbations in the solar wind pressure or IMF result in fast compressional mode waves that propagate through the magnetosphere and drive forced and resonant oscillations of geomagnetic field lines. The compressional wave field may also stimulate ionospheric perturbations. The observations demonstrate that HF radar ground scatter may contain important information on small-amplitude features, extending the scope and capability of these radars to track features in the ionosphere.


CUTLASS is supported by the Particle Physics and Astronomy Research Council (PPARC), UK, the Swedish Institute for Space Physics, Uppsala, and the Finnish Meteorological Institute (FMI), Helsinki. We thank D. K. Milling and I. R. Mann for providing the SAMNET data. SAMNET is a PPARC facility deployed and operated by the University of York. We also thank Lasse Hakkinen at FMI for the supply of IMAGE data, and all those who help maintain the array. WIND data were made available to the CDAWeb site by K. Ogilvie (SWE) and R. Lepping (MFI) at NASA/GSFC. IRIS is operated by the Department of Communications Systems at Lancaster University (UK), funded by PPARC in collaboration with the Sodankyla Geophysical Observatory. We ¨ are grateful to A. Rodger and M. Pinnock for helpful discussions. FWM received support from a PPARC Visiting Fellowship during this study.



Annales Geophysicae, 2003, 21 (2), pp. 559-576 (18)

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/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy


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Annales Geophysicae


European Geosciences Union (EGU), Copernicus Publications, Springer Verlag (Germany)





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