Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection
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...
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ftunivreading:oai:centaur.reading.ac.uk:38708 2024-09-15T18:04:30+00:00 Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection Davies, J. A. Yeoman, T. K. Rae, I. J. Milan, S. E. Lester, M. Lockwood, Mike McWilliams, A. 2002 text https://centaur.reading.ac.uk/38708/ https://centaur.reading.ac.uk/38708/1/207_Daviesetal_ang-20-781.pdf https://doi.org/10.5194/angeo-20-781-2002 en eng Copernicus Publications https://centaur.reading.ac.uk/38708/1/207_Daviesetal_ang-20-781.pdf Davies, J. A., Yeoman, T. K., Rae, I. J., Milan, S. E., Lester, M., Lockwood, M. <https://centaur.reading.ac.uk/view/creators/90001127.html> orcid:0000-0002-7397-2172 and McWilliams, A. (2002) Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection. Annales Geophysicae, 20 (6). pp. 781-794. ISSN 0992-7689 doi: https://doi.org/10.5194/angeo-20-781-2002 <https://doi.org/10.5194/angeo-20-781-2002> Article PeerReviewed 2002 ftunivreading https://doi.org/10.5194/angeo-20-781-2002 2024-06-25T14:57:10Z 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. Article in Journal/Newspaper EISCAT Northern Norway CentAUR: Central Archive at the University of Reading Annales Geophysicae 20 6 781 794 |
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Open Polar |
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CentAUR: Central Archive at the University of Reading |
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ftunivreading |
language |
English |
description |
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. |
format |
Article in Journal/Newspaper |
author |
Davies, J. A. Yeoman, T. K. Rae, I. J. Milan, S. E. Lester, M. Lockwood, Mike McWilliams, A. |
spellingShingle |
Davies, J. A. Yeoman, T. K. Rae, I. J. Milan, S. E. Lester, M. Lockwood, Mike McWilliams, A. Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection |
author_facet |
Davies, J. A. Yeoman, T. K. Rae, I. J. Milan, S. E. Lester, M. Lockwood, Mike McWilliams, A. |
author_sort |
Davies, J. A. |
title |
Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection |
title_short |
Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection |
title_full |
Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection |
title_fullStr |
Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection |
title_full_unstemmed |
Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection |
title_sort |
ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection |
publisher |
Copernicus Publications |
publishDate |
2002 |
url |
https://centaur.reading.ac.uk/38708/ https://centaur.reading.ac.uk/38708/1/207_Daviesetal_ang-20-781.pdf https://doi.org/10.5194/angeo-20-781-2002 |
genre |
EISCAT Northern Norway |
genre_facet |
EISCAT Northern Norway |
op_relation |
https://centaur.reading.ac.uk/38708/1/207_Daviesetal_ang-20-781.pdf Davies, J. A., Yeoman, T. K., Rae, I. J., Milan, S. E., Lester, M., Lockwood, M. <https://centaur.reading.ac.uk/view/creators/90001127.html> orcid:0000-0002-7397-2172 and McWilliams, A. (2002) Ground-based observations of the auroral zone and polar cap ionospheric responses to dayside transient reconnection. Annales Geophysicae, 20 (6). pp. 781-794. ISSN 0992-7689 doi: https://doi.org/10.5194/angeo-20-781-2002 <https://doi.org/10.5194/angeo-20-781-2002> |
op_doi |
https://doi.org/10.5194/angeo-20-781-2002 |
container_title |
Annales Geophysicae |
container_volume |
20 |
container_issue |
6 |
container_start_page |
781 |
op_container_end_page |
794 |
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1810441991932084224 |