Identification of Kelvin-Helmholtz generated vortices in magnetised fluids
The Kelvin-Helmholtz Instability (KHI), arising from velocity shear across the magnetopause, plays a significant role in the viscous-like transfer of mass, momentum, and energy from the shocked solar wind into the magnetosphere. While the KHI leads to growth of surface waves and vortices, suitable d...
| Main Authors: | , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Frontiers Media S.A.
2024-08-01
|
| Series: | Frontiers in Astronomy and Space Sciences |
| Subjects: | |
| Online Access: | https://www.frontiersin.org/articles/10.3389/fspas.2024.1431238/full |
| _version_ | 1827136125339172864 |
|---|---|
| author | Harley M. Kelly Martin O. Archer Xuanye Ma Katariina Nykyri Katariina Nykyri Jonathan P. Eastwood David J. Southwood |
| author_facet | Harley M. Kelly Martin O. Archer Xuanye Ma Katariina Nykyri Katariina Nykyri Jonathan P. Eastwood David J. Southwood |
| author_sort | Harley M. Kelly |
| collection | DOAJ |
| description | The Kelvin-Helmholtz Instability (KHI), arising from velocity shear across the magnetopause, plays a significant role in the viscous-like transfer of mass, momentum, and energy from the shocked solar wind into the magnetosphere. While the KHI leads to growth of surface waves and vortices, suitable detection methods for these applicable to magnetohydrodynamics (MHD) are currently lacking. A novel method is derived based on the well-established λ-family of hydrodynamic vortex identification techniques, which define a vortex as a local minimum in an adapted pressure field. The J×B Lorentz force is incorporated into this method by using an effective total pressure in MHD, including both magnetic pressure and a pressure-like part of the magnetic tension derived from a Helmholtz decomposition. The λMHD method is shown to comprise of four physical effects: vortical momentum, density gradients, fluid compressibility, and the rotational part of the magnetic tension. A local three-dimensional MHD simulation representative of near-flank magnetopause conditions (plasma β’s 0.5–5 and convective Mach numbers Mf∼0.4) under northward interplanetary magnetic field (IMF) is used to validate λMHD. Analysis shows it correlates well with hydrodynamic vortex definitions, though the level of correlation decreases with vortex evolution. Overall, vortical momentum dominates λMHD at all times. During the linear growth phase, density gradients act to oppose vortex formation. By the highly nonlinear stage, the formation of small-scale structures leads to a rising importance of the magnetic tension. Compressibility was found to be insignificant throughout. Finally, a demonstration of this method adapted to tetrahedral spacecraft observations is performed. |
| first_indexed | 2025-03-20T17:46:35Z |
| format | Article |
| id | doaj.art-ff71ab3c1c85498d8e3b64aff8c0b8f3 |
| institution | Directory Open Access Journal |
| issn | 2296-987X |
| language | English |
| last_indexed | 2025-03-20T17:46:35Z |
| publishDate | 2024-08-01 |
| publisher | Frontiers Media S.A. |
| record_format | Article |
| series | Frontiers in Astronomy and Space Sciences |
| spelling | doaj.art-ff71ab3c1c85498d8e3b64aff8c0b8f32024-08-28T06:00:56ZengFrontiers Media S.A.Frontiers in Astronomy and Space Sciences2296-987X2024-08-011110.3389/fspas.2024.14312381431238Identification of Kelvin-Helmholtz generated vortices in magnetised fluidsHarley M. Kelly0Martin O. Archer1Xuanye Ma2Katariina Nykyri3Katariina Nykyri4Jonathan P. Eastwood5David J. Southwood6Department of Physics, Space, Plasma, and Climate Community, Imperial College London, London, United KingdomDepartment of Physics, Space, Plasma, and Climate Community, Imperial College London, London, United KingdomPhysical Sciences Department, Embry Riddle Aeronautical University, Daytona Beach, FL, United StatesPhysical Sciences Department, Embry Riddle Aeronautical University, Daytona Beach, FL, United StatesNational Aeronautics and Space Administration (NASA), Goddard Space Flight Center, Greenbelt, MD, United StatesDepartment of Physics, Space, Plasma, and Climate Community, Imperial College London, London, United KingdomDepartment of Physics, Space, Plasma, and Climate Community, Imperial College London, London, United KingdomThe Kelvin-Helmholtz Instability (KHI), arising from velocity shear across the magnetopause, plays a significant role in the viscous-like transfer of mass, momentum, and energy from the shocked solar wind into the magnetosphere. While the KHI leads to growth of surface waves and vortices, suitable detection methods for these applicable to magnetohydrodynamics (MHD) are currently lacking. A novel method is derived based on the well-established λ-family of hydrodynamic vortex identification techniques, which define a vortex as a local minimum in an adapted pressure field. The J×B Lorentz force is incorporated into this method by using an effective total pressure in MHD, including both magnetic pressure and a pressure-like part of the magnetic tension derived from a Helmholtz decomposition. The λMHD method is shown to comprise of four physical effects: vortical momentum, density gradients, fluid compressibility, and the rotational part of the magnetic tension. A local three-dimensional MHD simulation representative of near-flank magnetopause conditions (plasma β’s 0.5–5 and convective Mach numbers Mf∼0.4) under northward interplanetary magnetic field (IMF) is used to validate λMHD. Analysis shows it correlates well with hydrodynamic vortex definitions, though the level of correlation decreases with vortex evolution. Overall, vortical momentum dominates λMHD at all times. During the linear growth phase, density gradients act to oppose vortex formation. By the highly nonlinear stage, the formation of small-scale structures leads to a rising importance of the magnetic tension. Compressibility was found to be insignificant throughout. Finally, a demonstration of this method adapted to tetrahedral spacecraft observations is performed.https://www.frontiersin.org/articles/10.3389/fspas.2024.1431238/fullKelvin-Helmholtz instabilitymagnetopausesurface wavevortex identificationsimulationsmagnetohydrodynamics |
| spellingShingle | Harley M. Kelly Martin O. Archer Xuanye Ma Katariina Nykyri Katariina Nykyri Jonathan P. Eastwood David J. Southwood Identification of Kelvin-Helmholtz generated vortices in magnetised fluids Frontiers in Astronomy and Space Sciences Kelvin-Helmholtz instability magnetopause surface wave vortex identification simulations magnetohydrodynamics |
| title | Identification of Kelvin-Helmholtz generated vortices in magnetised fluids |
| title_full | Identification of Kelvin-Helmholtz generated vortices in magnetised fluids |
| title_fullStr | Identification of Kelvin-Helmholtz generated vortices in magnetised fluids |
| title_full_unstemmed | Identification of Kelvin-Helmholtz generated vortices in magnetised fluids |
| title_short | Identification of Kelvin-Helmholtz generated vortices in magnetised fluids |
| title_sort | identification of kelvin helmholtz generated vortices in magnetised fluids |
| topic | Kelvin-Helmholtz instability magnetopause surface wave vortex identification simulations magnetohydrodynamics |
| url | https://www.frontiersin.org/articles/10.3389/fspas.2024.1431238/full |
| work_keys_str_mv | AT harleymkelly identificationofkelvinhelmholtzgeneratedvorticesinmagnetisedfluids AT martinoarcher identificationofkelvinhelmholtzgeneratedvorticesinmagnetisedfluids AT xuanyema identificationofkelvinhelmholtzgeneratedvorticesinmagnetisedfluids AT katariinanykyri identificationofkelvinhelmholtzgeneratedvorticesinmagnetisedfluids AT katariinanykyri identificationofkelvinhelmholtzgeneratedvorticesinmagnetisedfluids AT jonathanpeastwood identificationofkelvinhelmholtzgeneratedvorticesinmagnetisedfluids AT davidjsouthwood identificationofkelvinhelmholtzgeneratedvorticesinmagnetisedfluids |