Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI
Abstract Omega bands are curved aurora forms that evolve from a quiet arc located along the poleward edge of a diffuse auroral band within the midnight to morningside auroral oval. They usually propagate eastward. Because omega bands are a significant contributor to an active magnetotail, knowledge...
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2018-02-01
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| Series: | Geophysical Research Letters |
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| Online Access: | https://doi.org/10.1002/2017GL076485 |
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| author | Jiang Liu L. R. Lyons W. E. Archer B. Gallardo‐Lacourt Y. Nishimura Ying Zou C. Gabrielse J. M. Weygand |
| author_facet | Jiang Liu L. R. Lyons W. E. Archer B. Gallardo‐Lacourt Y. Nishimura Ying Zou C. Gabrielse J. M. Weygand |
| author_sort | Jiang Liu |
| collection | DOAJ |
| description | Abstract Omega bands are curved aurora forms that evolve from a quiet arc located along the poleward edge of a diffuse auroral band within the midnight to morningside auroral oval. They usually propagate eastward. Because omega bands are a significant contributor to an active magnetotail, knowledge about their generation is important for understanding tail dynamics. Previous studies have shown that auroral streamers, footprints of fast flows in the tail, can propagate into omega bands. Such events, however, are limited, and it is still unclear whether and how the flows trigger the bands. The ionospheric flows associated with omega bands may provide valuable information on the driving mechanisms of the bands. We examine these flows taking advantage of the conjunctions between the Swarm spacecraft and Time History of Events and Macroscale Interactions during Substorms all‐sky imagers, which allow us to demonstrate the relative location of the flows to the omega bands' bright arcs for the first time. We find that a strong eastward ionospheric flow is consistently present immediately poleward of the omega band's bright arc, resulting in a sharp flow shear near the poleward boundary of the band. This ionospheric flow shear should correspond to a flow shear near the inner edge of the plasma sheet. This plasma sheet shear may drive a Kelvin‐Helmholz instability which then distorts the quiet arc to form omega bands. It seems plausible that the strong eastward flows are driven by streamer‐related fast flows or enhanced convection in the magnetotail. |
| format | Article |
| id | doaj-art-f3052d00a35b4a0fb6b6b08ed3d503f3 |
| institution | Kabale University |
| issn | 0094-8276 1944-8007 |
| language | English |
| publishDate | 2018-02-01 |
| publisher | Wiley |
| record_format | Article |
| series | Geophysical Research Letters |
| spelling | doaj-art-f3052d00a35b4a0fb6b6b08ed3d503f32025-08-20T03:49:46ZengWileyGeophysical Research Letters0094-82761944-80072018-02-014531218122710.1002/2017GL076485Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASIJiang Liu0L. R. Lyons1W. E. Archer2B. Gallardo‐Lacourt3Y. Nishimura4Ying Zou5C. Gabrielse6J. M. Weygand7Department of Atmospheric and Oceanic Sciences University of California Los Angeles CA USADepartment of Atmospheric and Oceanic Sciences University of California Los Angeles CA USADepartment of Physics and Engineering Physics University of Saskatchewan Saskatoon Saskatchewan CanadaDepartment of Physics and Astronomy University of Calgary Calgary Alberta CanadaDepartment of Astronomy and Center for Space Physics Boston University Boston MA USADepartment of Astronomy and Center for Space Physics Boston University Boston MA USADepartment of Atmospheric and Oceanic Sciences University of California Los Angeles CA USADepartment of Earth, Planetary and Space Sciences and Institute of Geophysics and Planetary Physics University of California Los Angeles CA USAAbstract Omega bands are curved aurora forms that evolve from a quiet arc located along the poleward edge of a diffuse auroral band within the midnight to morningside auroral oval. They usually propagate eastward. Because omega bands are a significant contributor to an active magnetotail, knowledge about their generation is important for understanding tail dynamics. Previous studies have shown that auroral streamers, footprints of fast flows in the tail, can propagate into omega bands. Such events, however, are limited, and it is still unclear whether and how the flows trigger the bands. The ionospheric flows associated with omega bands may provide valuable information on the driving mechanisms of the bands. We examine these flows taking advantage of the conjunctions between the Swarm spacecraft and Time History of Events and Macroscale Interactions during Substorms all‐sky imagers, which allow us to demonstrate the relative location of the flows to the omega bands' bright arcs for the first time. We find that a strong eastward ionospheric flow is consistently present immediately poleward of the omega band's bright arc, resulting in a sharp flow shear near the poleward boundary of the band. This ionospheric flow shear should correspond to a flow shear near the inner edge of the plasma sheet. This plasma sheet shear may drive a Kelvin‐Helmholz instability which then distorts the quiet arc to form omega bands. It seems plausible that the strong eastward flows are driven by streamer‐related fast flows or enhanced convection in the magnetotail.https://doi.org/10.1002/2017GL076485omega bandflow shearaurorasubstormionospheric flowKelvin‐Helmholz instability |
| spellingShingle | Jiang Liu L. R. Lyons W. E. Archer B. Gallardo‐Lacourt Y. Nishimura Ying Zou C. Gabrielse J. M. Weygand Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI Geophysical Research Letters omega band flow shear aurora substorm ionospheric flow Kelvin‐Helmholz instability |
| title | Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI |
| title_full | Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI |
| title_fullStr | Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI |
| title_full_unstemmed | Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI |
| title_short | Flow Shears at the Poleward Boundary of Omega Bands Observed During Conjunctions of Swarm and THEMIS ASI |
| title_sort | flow shears at the poleward boundary of omega bands observed during conjunctions of swarm and themis asi |
| topic | omega band flow shear aurora substorm ionospheric flow Kelvin‐Helmholz instability |
| url | https://doi.org/10.1002/2017GL076485 |
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