Velocity shear instability and plasma billows at the Earth's magnetic boundary
The Kelvin-Helmoltz instability (KH) with formation of vortices appears in a wide variety of terrestrial, interplanetary, and astrophysical contexts. We study a series of iterated rolled-up coherent plasma structures (15) that flow in the equatorial Earth's boundary layer (BL), observed on Octo...
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2012
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| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_17426588_v370_n1_p_Gratton https://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=artiaex&d=paper_17426588_v370_n1_p_Gratton_oai |
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I28-R145-paper_17426588_v370_n1_p_Gratton_oai2024-08-16 Gratton, F.T. Gnavi, G. Farrugia, C.J. Bilbao, L. Torbert, R. 2012 The Kelvin-Helmoltz instability (KH) with formation of vortices appears in a wide variety of terrestrial, interplanetary, and astrophysical contexts. We study a series of iterated rolled-up coherent plasma structures (15) that flow in the equatorial Earth's boundary layer (BL), observed on October 24, 2001. The data were recorded during a 1.5 hour-long Wind crossing of the BL at the dawn magnetospheric flank, tailward of the terminator (X≈-13 RE). The interplanetary magnetic field (IMF) was radially directed, almost antiparallel to the magnetosheath (MS) flow. This configuration is expected to be adverse to the KH instability because of the collinearity of field and flow, and the high compressibility of the MS. We analyze the BL stability with compressible MHD theory using continuous profiles for the physical quantities. Upstream, at near Earth sites, we input parameters derived from an exact MHD solution for collinear flows. Further downtail at Wind position we input measured parameters. The BL is found KH unstable in spite of unfavorable features of the external flow. On the experimental side, the passage of vortices is inferred from the presence of low density - hot plasma being accelerated to speeds higher than that of the contiguous MS. It is further supported by the peculiar correlation of relative motions (in the bulk velocity frame): cold-dense plasma drifts sunward, while hot-tenuous plasma moves tailward. This event differs from many other studies that reported BL vortices under strongly northward IMF orientations. This is a case of KH vortices observed under an almost radial IMF, with implicit significance for the more common Parker's spiral fields, and the problem of plasma entry in the magnetosphere. Fil:Gratton, F.T. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Gnavi, G. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Fil:Bilbao, L. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. application/pdf http://hdl.handle.net/20.500.12110/paper_17426588_v370_n1_p_Gratton info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by/2.5/ar J. Phys. Conf. Ser. 2012;370(1) Boundary layers Magnetoplasma Magnetosphere Plasma diagnostics Plasma stability Shear flow Stability Vortex flow Continuous profile Input parameter Interplanetary magnetic fields Kelvin-Helmoltz instability Measured parameters Physical quantities Plasma structure Relative motion Magnetohydrodynamics Velocity shear instability and plasma billows at the Earth's magnetic boundary info:eu-repo/semantics/conferenceObject info:ar-repo/semantics/documento de conferencia info:eu-repo/semantics/publishedVersion https://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=artiaex&d=paper_17426588_v370_n1_p_Gratton_oai |
| institution |
Universidad de Buenos Aires |
| institution_str |
I-28 |
| repository_str |
R-145 |
| collection |
Repositorio Digital de la Universidad de Buenos Aires (UBA) |
| topic |
Boundary layers Magnetoplasma Magnetosphere Plasma diagnostics Plasma stability Shear flow Stability Vortex flow Continuous profile Input parameter Interplanetary magnetic fields Kelvin-Helmoltz instability Measured parameters Physical quantities Plasma structure Relative motion Magnetohydrodynamics |
| spellingShingle |
Boundary layers Magnetoplasma Magnetosphere Plasma diagnostics Plasma stability Shear flow Stability Vortex flow Continuous profile Input parameter Interplanetary magnetic fields Kelvin-Helmoltz instability Measured parameters Physical quantities Plasma structure Relative motion Magnetohydrodynamics Gratton, F.T. Gnavi, G. Farrugia, C.J. Bilbao, L. Torbert, R. Velocity shear instability and plasma billows at the Earth's magnetic boundary |
| topic_facet |
Boundary layers Magnetoplasma Magnetosphere Plasma diagnostics Plasma stability Shear flow Stability Vortex flow Continuous profile Input parameter Interplanetary magnetic fields Kelvin-Helmoltz instability Measured parameters Physical quantities Plasma structure Relative motion Magnetohydrodynamics |
| description |
The Kelvin-Helmoltz instability (KH) with formation of vortices appears in a wide variety of terrestrial, interplanetary, and astrophysical contexts. We study a series of iterated rolled-up coherent plasma structures (15) that flow in the equatorial Earth's boundary layer (BL), observed on October 24, 2001. The data were recorded during a 1.5 hour-long Wind crossing of the BL at the dawn magnetospheric flank, tailward of the terminator (X≈-13 RE). The interplanetary magnetic field (IMF) was radially directed, almost antiparallel to the magnetosheath (MS) flow. This configuration is expected to be adverse to the KH instability because of the collinearity of field and flow, and the high compressibility of the MS. We analyze the BL stability with compressible MHD theory using continuous profiles for the physical quantities. Upstream, at near Earth sites, we input parameters derived from an exact MHD solution for collinear flows. Further downtail at Wind position we input measured parameters. The BL is found KH unstable in spite of unfavorable features of the external flow. On the experimental side, the passage of vortices is inferred from the presence of low density - hot plasma being accelerated to speeds higher than that of the contiguous MS. It is further supported by the peculiar correlation of relative motions (in the bulk velocity frame): cold-dense plasma drifts sunward, while hot-tenuous plasma moves tailward. This event differs from many other studies that reported BL vortices under strongly northward IMF orientations. This is a case of KH vortices observed under an almost radial IMF, with implicit significance for the more common Parker's spiral fields, and the problem of plasma entry in the magnetosphere. |
| format |
Documento de conferencia Documento de conferencia publishedVersion |
| author |
Gratton, F.T. Gnavi, G. Farrugia, C.J. Bilbao, L. Torbert, R. |
| author_facet |
Gratton, F.T. Gnavi, G. Farrugia, C.J. Bilbao, L. Torbert, R. |
| author_sort |
Gratton, F.T. |
| title |
Velocity shear instability and plasma billows at the Earth's magnetic boundary |
| title_short |
Velocity shear instability and plasma billows at the Earth's magnetic boundary |
| title_full |
Velocity shear instability and plasma billows at the Earth's magnetic boundary |
| title_fullStr |
Velocity shear instability and plasma billows at the Earth's magnetic boundary |
| title_full_unstemmed |
Velocity shear instability and plasma billows at the Earth's magnetic boundary |
| title_sort |
velocity shear instability and plasma billows at the earth's magnetic boundary |
| publishDate |
2012 |
| url |
http://hdl.handle.net/20.500.12110/paper_17426588_v370_n1_p_Gratton https://repositoriouba.sisbi.uba.ar/gsdl/cgi-bin/library.cgi?a=d&c=artiaex&d=paper_17426588_v370_n1_p_Gratton_oai |
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| _version_ |
1809356933054857216 |