Statistical study of high-latitude plasma flow during magnetospheric substorms
We have utilised the near-global imaging capabilities of the Northern Hemisphere SuperDARN radars, to perform a statistical superposed epoch analysis of high-latitude plasma flows during magnetospheric substorms. The study involved 67 substorms, identified using the IMAGE FUV space-borne auroral...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2004-11-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/22/3607/2004/angeo-22-3607-2004.pdf |
| _version_ | 1811273588733378560 |
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| author | G. Provan M. Lester S. B. Mende S. E. Milan |
| author_facet | G. Provan M. Lester S. B. Mende S. E. Milan |
| author_sort | G. Provan |
| collection | DOAJ |
| description | We have utilised the near-global imaging capabilities of the Northern Hemisphere
SuperDARN radars, to perform a statistical superposed epoch
analysis of high-latitude plasma flows during magnetospheric substorms. The
study involved 67 substorms, identified using the IMAGE FUV space-borne
auroral imager. A substorm co-ordinate system was developed, centred on the
magnetic local time and magnetic latitude of substorm onset determined from
the auroral images. The plasma flow vectors from all 67 intervals were
combined, creating global statistical plasma flow patterns and backscatter
occurrence statistics during the substorm growth and expansion phases. The
commencement of the substorm growth phase was clearly observed in the radar
data 18-20min before substorm onset, with an increase in the
anti-sunward component of the plasma velocity flowing across dawn sector of
the polar cap and a peak in the dawn-to-dusk transpolar voltage. Nightside
backscatter moved to lower latitudes as the growth phase progressed. At
substorm onset a flow suppression region was observed on the nightside, with
fast flows surrounding the suppressed flow region. The dawn-to-dusk
transpolar voltage increased from ~40kV just before substorm onset to
~75kV 12min after onset. The low-latitude return flow started to
increase at substorm onset and continued to increase until 8min after
onset. The velocity flowing across the polar-cap peaked 12-14min after
onset. This increase in the flux of the polar cap and the excitation of
large-scale plasma flow occurred even though the IMF <i>B<sub>z</sub></i> component was
increasing (becoming less negative) during most of this time. This study is
the first to statistically prove that nightside reconnection creates
magnetic flux and excites high-latitude plasma flow in a similar way to
dayside reconnection and that dayside and nightside reconnection, are two
separate time-dependent processes. |
| first_indexed | 2024-04-12T23:01:57Z |
| format | Article |
| id | doaj.art-07f42f5542384e758e7f10abe5bb3b8f |
| institution | Directory Open Access Journal |
| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-04-12T23:01:57Z |
| publishDate | 2004-11-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-07f42f5542384e758e7f10abe5bb3b8f2022-12-22T03:13:02ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762004-11-01223607362410.5194/angeo-22-3607-2004Statistical study of high-latitude plasma flow during magnetospheric substormsG. Provan0M. Lester1S. B. Mende2S. E. Milan3Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UKDepartment of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UKSpace Science Laboratory, University of California, Berkeley, California, USADepartment of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UKWe have utilised the near-global imaging capabilities of the Northern Hemisphere SuperDARN radars, to perform a statistical superposed epoch analysis of high-latitude plasma flows during magnetospheric substorms. The study involved 67 substorms, identified using the IMAGE FUV space-borne auroral imager. A substorm co-ordinate system was developed, centred on the magnetic local time and magnetic latitude of substorm onset determined from the auroral images. The plasma flow vectors from all 67 intervals were combined, creating global statistical plasma flow patterns and backscatter occurrence statistics during the substorm growth and expansion phases. The commencement of the substorm growth phase was clearly observed in the radar data 18-20min before substorm onset, with an increase in the anti-sunward component of the plasma velocity flowing across dawn sector of the polar cap and a peak in the dawn-to-dusk transpolar voltage. Nightside backscatter moved to lower latitudes as the growth phase progressed. At substorm onset a flow suppression region was observed on the nightside, with fast flows surrounding the suppressed flow region. The dawn-to-dusk transpolar voltage increased from ~40kV just before substorm onset to ~75kV 12min after onset. The low-latitude return flow started to increase at substorm onset and continued to increase until 8min after onset. The velocity flowing across the polar-cap peaked 12-14min after onset. This increase in the flux of the polar cap and the excitation of large-scale plasma flow occurred even though the IMF <i>B<sub>z</sub></i> component was increasing (becoming less negative) during most of this time. This study is the first to statistically prove that nightside reconnection creates magnetic flux and excites high-latitude plasma flow in a similar way to dayside reconnection and that dayside and nightside reconnection, are two separate time-dependent processes.https://www.ann-geophys.net/22/3607/2004/angeo-22-3607-2004.pdf |
| spellingShingle | G. Provan M. Lester S. B. Mende S. E. Milan Statistical study of high-latitude plasma flow during magnetospheric substorms Annales Geophysicae |
| title | Statistical study of high-latitude plasma flow during magnetospheric substorms |
| title_full | Statistical study of high-latitude plasma flow during magnetospheric substorms |
| title_fullStr | Statistical study of high-latitude plasma flow during magnetospheric substorms |
| title_full_unstemmed | Statistical study of high-latitude plasma flow during magnetospheric substorms |
| title_short | Statistical study of high-latitude plasma flow during magnetospheric substorms |
| title_sort | statistical study of high latitude plasma flow during magnetospheric substorms |
| url | https://www.ann-geophys.net/22/3607/2004/angeo-22-3607-2004.pdf |
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