Two-dimensional electric field measurements in the ionospheric footprint of a flux transfer event

McWilliams, K. A.; Yeoman, T. K.; Cowley, S. W. H.

doi:10.1007/s00585-001-1584-2

Cited by 40 publications

(29 citation statements)

References 25 publications

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“…signatures which, although generated by FTE activity, persist beyond the interval of active reconnection. Observations presented by McWilliams et al (2001) suggested that only for the first part of its lifetime in the radar field-of-view, did an HF transient map the footprint of an active reconnection region, moving mainly longitudinally under the magnetic tension force induced by the IMF B Y component and with a phase velocity roughly twice the convection speed. After this, the transient slowed to the convection velocity, moving antisunward with the reconnected field lines.…”

Section: Cutlass Hf Observationsmentioning

confidence: 99%

“…After this, the transient slowed to the convection velocity, moving antisunward with the reconnected field lines. It should be stated that the study of McWilliams et al (2001) was exceptional in that twodimensional vector observations of the convection pattern were available throughout the ionospheric footprint of an FTE. The authors noticed a reduction in the spectral width of the feature as it propagated, as is also evident in the present observations.…”

Section: Cutlass Hf Observationsmentioning

confidence: 99%

“…The authors noticed a reduction in the spectral width of the feature as it propagated, as is also evident in the present observations. It is deemed likely, although this was not stated explicitly by McWilliams et al (2001), that the reduction in spectral width reflects the PMRAF leaving the region of active reconnection. This is very much confirmed by the fact that in the region 1 scatter they are accompanied by PIFs and this is not so in the region 2 scatter.…”

Section: Cutlass Hf Observationsmentioning

confidence: 99%

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Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection

et al. 2002

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Abstract.Observations from the EISCAT VHF incoherent scatter radar system in northern Norway, during a run of the common programme CP-4, reveal a series of polewardpropagating F-region electron density enhancements in the pre-noon sector on 23 November 1999. These plasma density features, which are observed under conditions of a strongly southward interplanetary magnetic field, exhibit a recurrence rate of under 10 min and appear to emanate from the vicinity of the open/closed field-line boundary from where they travel into the polar cap; this is suggestive of their being an ionospheric response to transient reconnection at the dayside magnetopause (flux transfer events). Simultaneous with the density structures detected by the VHF radar, polewardmoving radar auroral forms (PMRAFs) are observed by the Finland HF coherent scatter radar. It is thought that PMRAFs, which are commonly observed near local noon by HF radars, are also related to flux transfer events, although the specific mechanism for the generation of the field-aligned irregularities within such features is not well understood. The HF observations suggest, that for much of their existence, the PMRAFs trace fossil signatures of transient reconnection rather than revealing the footprint of active reconnection itself; this is evidenced not least by the fact that the PMRAFs become narrower in spectral width as they evolve away from the region of more classical, broad cusp scatter in which they originate. Interpretation of the HF observations with reference to the plasma parameters diagnosed by the incoherent scatter radar suggests that as the PMRAFs migrate away from the reconnection site and across the polar cap, entrained in the ambient antisunward flow, the irregularities therein are generated by the presence of gradients in the electron density, with these gradients having been formed through structuring of the ionosphere in the cusp region in response to transient reconnection.

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Section: Cutlass Hf Observationsmentioning

confidence: 99%

Section: Cutlass Hf Observationsmentioning

confidence: 99%

Section: Cutlass Hf Observationsmentioning

confidence: 99%

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Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection

et al. 2002

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“…Hosokawa et al (2002) carried out a statistical analysis of the HF radar spectral width and reported that the spectral width is small above 80 • magnetic latitude. McWilliams et al (2001a) investigated poleward moving pulsed ionospheric flows (PIFs) in the HF radar data and pointed out that the spectral widths are relatively high at the equatorward edge of the PIFs, but decrease with increasing latitude. Milan et al (2002) analyzed HF radar polar patches and clearly showed that the spectral width within the patch becomes considerably narrow as it moves poleward.…”

Section: Discussionmentioning

confidence: 99%

Origin of the SuperDARN broad Doppler spectra:simultaneous observation with Oersted satellite magnetometer

et al. 2004

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Abstract. We perform a case study of a favorable conjunction of an overpass of the Oersted satellite with the field-ofview of the SuperDARN Syowa East radar during an interval of the southward IMF B z . At the time, the radar observed an L-shell aligned boundary in the spectral width around the dayside ionosphere. Simultaneously, high-frequency (0.2-5 Hz) magnetic field fluctuations were observed by the Oersted satellite's high-time resolution magnetometer. These magnetic field fluctuations are considered to be Alfvén waves possibly associated with the particle which precipitates into the dayside high-latitude ionosphere when magnetic reconnection occurs. It has been theoretically predicted that the time-varying electric field is the dominant physical process to expand the broad HF radar Doppler spectra. Our observation clearly demonstrates that the boundary between narrow and broad spectral widths is corresponding well to the boundary in the level of the fluctuations, which supports the previous theoretical prediction. A close relationship between electric and magnetic field fluctuations and particle precipitations during southward IMF conditions has been confirmed by many authors. The present observation allows us to suggest that the boundary between narrow and broad Doppler spectral widths observed in the dayside ionosphere is connected with the signature of the open/closed field line boundary, such as the cusp particle precipitations via electric and magnetic field fluctuations for the case of the negative IMF B z conditions.

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“…The relationship between PIFs, FCEs and FTEs is discussed more thoroughly in Wild et al (2001). A detailed discussion of the mapping of FTEs to the ionosphere in PIFs appears in McWilliams et al (2001).…”

Section: Effects Of Solar Wind Variationsmentioning

confidence: 99%

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

et al. 2003

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Abstract.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 m s −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.

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Two-dimensional electric field measurements in the ionospheric footprint of a flux transfer event

Cited by 40 publications

References 25 publications

Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection

Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection

Origin of the SuperDARN broad Doppler spectra:simultaneous observation with Oersted satellite magnetometer

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

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