Characteristics of merging at the magnetopause inferred from dayside 557.7-nm all-sky images: IMF drivers of poleward moving auroral forms
We combine in situ measurements from Cluster with high-resolution 557.7 nm all-sky images from South Pole to investigate the spatial and temporal evolution of merging on the dayside magnetopause. Variations of 557.7 nm emissions were observed at a 6 s cadence at South Pole on 29 April 2003 while...
| Main Authors: | , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2006-11-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/24/3071/2006/angeo-24-3071-2006.pdf |
| _version_ | 1818931006169677824 |
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| author | N. C. Maynard W. J. Burke Y. Ebihara D. M. Ober D. M. Ober G. R. Wilson G. R. Wilson K. D. Siebert K. D. Siebert J. D. Winningham L. J. Lanzerotti C. J. Farrugia M. Ejiri H. Rème A. Balogh A. Fazakerley |
| author_facet | N. C. Maynard W. J. Burke Y. Ebihara D. M. Ober D. M. Ober G. R. Wilson G. R. Wilson K. D. Siebert K. D. Siebert J. D. Winningham L. J. Lanzerotti C. J. Farrugia M. Ejiri H. Rème A. Balogh A. Fazakerley |
| author_sort | N. C. Maynard |
| collection | DOAJ |
| description | We combine in situ measurements from Cluster with high-resolution 557.7 nm
all-sky images from South Pole to investigate the spatial and temporal
evolution of merging on the dayside magnetopause. Variations of 557.7 nm
emissions were observed at a 6 s cadence at South Pole on 29 April 2003
while significant changes in the Interplanetary Magnetic Field (IMF) clock
angle were reaching the magnetopause. Electrons energized at merging sites
are the probable sources for 557.7 nm cusp emissions. At the same time
Cluster was crossing the pre-noon cusp in the Northern Hemisphere. The
combined observations confirm results of a previous study that merging events
can occur at multiple sites simultaneously and vary asynchronously on time
scales of 10 s to 3 min (Maynard et al., 2004). The intensity of the
emissions and the merging rate appear to vary with changes in the IMF clock
angle, IMF <i>B<sub>X</sub></i> and the dynamic pressure of the solar wind. Most poleward
moving auroral forms (PMAFs) reflect responses to changes in interplanetary
medium rather than to local processes. The changes in magnetopause position
required by increases in dynamic pressure are mediated by merging and result
in the generation of PMAFs. Small (15–20%) variations in dynamic pressure
of the solar wind are sufficient to launch PMAFs. Changes in IMF <i>B<sub>X</sub></i> create
magnetic flux compressions and rarefactions in the solar wind. Increases
(decreases) in IMF <i>B<sub>X</sub></i> strengthens |<b>B</b>| near northern (southern)
hemisphere merging sites thereby enhancing merging rates and triggering
PMAFs. When correlating responses in the two hemispheres, the presence of
significant IMF <i>B<sub>X</sub></i> also requires that different lag-times be applied to
ACE measurements acquired ~0.1 AU upstream of Earth. Cluster
observations set lag times for merging at Northern Hemisphere sites;
post-noon optical emissions set times of Southern Hemisphere merging. All-sky
images and magnetohydrodynamic simulations indicate that merging occurs in
multiple discrete locations, rather than continuously, across the dayside for
southward IMF conditions in the presence of dipole tilt. Matching optical
signatures with clock-angle, <i>B<sub>X</sub></i>, and dynamic pressure variations provides
new insights about interplanetary control of dayside merging and associated
auroral dynamics. |
| first_indexed | 2024-12-20T04:09:43Z |
| format | Article |
| id | doaj.art-0bb2ccaf2566405b86320ab41753083a |
| institution | Directory Open Access Journal |
| issn | 0992-7689 1432-0576 |
| language | English |
| last_indexed | 2024-12-20T04:09:43Z |
| publishDate | 2006-11-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Annales Geophysicae |
| spelling | doaj.art-0bb2ccaf2566405b86320ab41753083a2022-12-21T19:53:56ZengCopernicus PublicationsAnnales Geophysicae0992-76891432-05762006-11-01243071309810.5194/angeo-24-3071-2006Characteristics of merging at the magnetopause inferred from dayside 557.7-nm all-sky images: IMF drivers of poleward moving auroral formsN. C. Maynard0W. J. Burke1Y. Ebihara2D. M. Ober3D. M. Ober4G. R. Wilson5G. R. Wilson6K. D. Siebert7K. D. Siebert8J. D. Winningham9L. J. Lanzerotti10C. J. Farrugia11M. Ejiri12H. Rème13A. Balogh14A. Fazakerley15Space Science Center, University of New Hampshire, Durham, NH, USAAir Force Research Laboratory, Hanscom Air Force Base, MA, USANational Institute of Polar Research, Tokyo, JapanATK Mission Research, Nashua, NH, USAnow at: Boston College, Chestnut Hill, MA, USAATK Mission Research, Nashua, NH, USAnow at: Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL, USAATK Mission Research, Nashua, NH, USAnow at: SPARTA, Inc., Nashua, NH, USASouthwest Research Institute, San Antonio, TX, USANew Jersey Institute of Technology, NJ, USASpace Science Center, University of New Hampshire, Durham, NH, USANational Institute of Polar Research, Tokyo, JapanCESR/CNRS, Avenue du Colonel Roche, 31028 Toulouse, Cedex 4, FranceImperial College, Exhibition Road, London SW7 2BW, UKMullard Space Science Laboratory, Dorking, Surrey RH5 6NT, UKWe combine in situ measurements from Cluster with high-resolution 557.7 nm all-sky images from South Pole to investigate the spatial and temporal evolution of merging on the dayside magnetopause. Variations of 557.7 nm emissions were observed at a 6 s cadence at South Pole on 29 April 2003 while significant changes in the Interplanetary Magnetic Field (IMF) clock angle were reaching the magnetopause. Electrons energized at merging sites are the probable sources for 557.7 nm cusp emissions. At the same time Cluster was crossing the pre-noon cusp in the Northern Hemisphere. The combined observations confirm results of a previous study that merging events can occur at multiple sites simultaneously and vary asynchronously on time scales of 10 s to 3 min (Maynard et al., 2004). The intensity of the emissions and the merging rate appear to vary with changes in the IMF clock angle, IMF <i>B<sub>X</sub></i> and the dynamic pressure of the solar wind. Most poleward moving auroral forms (PMAFs) reflect responses to changes in interplanetary medium rather than to local processes. The changes in magnetopause position required by increases in dynamic pressure are mediated by merging and result in the generation of PMAFs. Small (15–20%) variations in dynamic pressure of the solar wind are sufficient to launch PMAFs. Changes in IMF <i>B<sub>X</sub></i> create magnetic flux compressions and rarefactions in the solar wind. Increases (decreases) in IMF <i>B<sub>X</sub></i> strengthens |<b>B</b>| near northern (southern) hemisphere merging sites thereby enhancing merging rates and triggering PMAFs. When correlating responses in the two hemispheres, the presence of significant IMF <i>B<sub>X</sub></i> also requires that different lag-times be applied to ACE measurements acquired ~0.1 AU upstream of Earth. Cluster observations set lag times for merging at Northern Hemisphere sites; post-noon optical emissions set times of Southern Hemisphere merging. All-sky images and magnetohydrodynamic simulations indicate that merging occurs in multiple discrete locations, rather than continuously, across the dayside for southward IMF conditions in the presence of dipole tilt. Matching optical signatures with clock-angle, <i>B<sub>X</sub></i>, and dynamic pressure variations provides new insights about interplanetary control of dayside merging and associated auroral dynamics.https://www.ann-geophys.net/24/3071/2006/angeo-24-3071-2006.pdf |
| spellingShingle | N. C. Maynard W. J. Burke Y. Ebihara D. M. Ober D. M. Ober G. R. Wilson G. R. Wilson K. D. Siebert K. D. Siebert J. D. Winningham L. J. Lanzerotti C. J. Farrugia M. Ejiri H. Rème A. Balogh A. Fazakerley Characteristics of merging at the magnetopause inferred from dayside 557.7-nm all-sky images: IMF drivers of poleward moving auroral forms Annales Geophysicae |
| title | Characteristics of merging at the magnetopause inferred from dayside 557.7-nm all-sky images: IMF drivers of poleward moving auroral forms |
| title_full | Characteristics of merging at the magnetopause inferred from dayside 557.7-nm all-sky images: IMF drivers of poleward moving auroral forms |
| title_fullStr | Characteristics of merging at the magnetopause inferred from dayside 557.7-nm all-sky images: IMF drivers of poleward moving auroral forms |
| title_full_unstemmed | Characteristics of merging at the magnetopause inferred from dayside 557.7-nm all-sky images: IMF drivers of poleward moving auroral forms |
| title_short | Characteristics of merging at the magnetopause inferred from dayside 557.7-nm all-sky images: IMF drivers of poleward moving auroral forms |
| title_sort | characteristics of merging at the magnetopause inferred from dayside 557 7 nm all sky images imf drivers of poleward moving auroral forms |
| url | https://www.ann-geophys.net/24/3071/2006/angeo-24-3071-2006.pdf |
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