Imbalanced Turbulence Modified by Large-scale Velocity Shears in the Solar Wind
We have investigated how the degree of imbalance in solar wind turbulence is modified by large-scale velocity shears in the solar wind plasma. The balance between counterpropagating Alfvénic fluctuations, which interact nonlinearly to generate the turbulence, has been quantified by the cross helicit...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astrophysical Journal Letters |
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| Online Access: | https://doi.org/10.3847/2041-8213/acc071 |
| _version_ | 1827830899393167360 |
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| author | Juska E. Soljento Simon W. Good Adnane Osmane Emilia K. J. Kilpua |
| author_facet | Juska E. Soljento Simon W. Good Adnane Osmane Emilia K. J. Kilpua |
| author_sort | Juska E. Soljento |
| collection | DOAJ |
| description | We have investigated how the degree of imbalance in solar wind turbulence is modified by large-scale velocity shears in the solar wind plasma. The balance between counterpropagating Alfvénic fluctuations, which interact nonlinearly to generate the turbulence, has been quantified by the cross helicity and Elsasser ratio. Velocity shears at a 30 minute timescale were identified, with the shear amplitude defined in terms of the linear Kelvin–Helmholtz (KH) instability threshold. The shears were associated with 74 interplanetary coronal mass ejection (ICME) sheaths observed by the Wind spacecraft at 1 au between 1997 and 2018. Typically weaker shears upstream of the sheaths and downstream in the ICME ejecta were also analyzed. In shears below the KH threshold, imbalance was approximately invariant or weakly rising with shear amplitude. Above the KH threshold, fluctuations tended toward a balanced state with increasing shear amplitude. Magnetic compressibility was also found to increase above the KH threshold. These findings are consistent with velocity shears being local sources of sunward fluctuations that act to reduce net imbalances in the antisunward direction, and suggest that the KH instability plays a role in this process. |
| first_indexed | 2024-03-12T04:36:09Z |
| format | Article |
| id | doaj.art-7d37bc13158f45e8b30f83e19fb4d517 |
| institution | Directory Open Access Journal |
| issn | 2041-8205 |
| language | English |
| last_indexed | 2024-03-12T04:36:09Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal Letters |
| spelling | doaj.art-7d37bc13158f45e8b30f83e19fb4d5172023-09-03T09:55:30ZengIOP PublishingThe Astrophysical Journal Letters2041-82052023-01-019461L1910.3847/2041-8213/acc071Imbalanced Turbulence Modified by Large-scale Velocity Shears in the Solar WindJuska E. Soljento0https://orcid.org/0000-0003-2495-8881Simon W. Good1https://orcid.org/0000-0002-4921-4208Adnane Osmane2https://orcid.org/0000-0003-2555-5953Emilia K. J. Kilpua3https://orcid.org/0000-0002-4489-8073Department of Physics, University of Helsinki , Helsinki, Finland ; juska.soljento@helsinki.fiDepartment of Physics, University of Helsinki , Helsinki, Finland ; juska.soljento@helsinki.fiDepartment of Physics, University of Helsinki , Helsinki, Finland ; juska.soljento@helsinki.fiDepartment of Physics, University of Helsinki , Helsinki, Finland ; juska.soljento@helsinki.fiWe have investigated how the degree of imbalance in solar wind turbulence is modified by large-scale velocity shears in the solar wind plasma. The balance between counterpropagating Alfvénic fluctuations, which interact nonlinearly to generate the turbulence, has been quantified by the cross helicity and Elsasser ratio. Velocity shears at a 30 minute timescale were identified, with the shear amplitude defined in terms of the linear Kelvin–Helmholtz (KH) instability threshold. The shears were associated with 74 interplanetary coronal mass ejection (ICME) sheaths observed by the Wind spacecraft at 1 au between 1997 and 2018. Typically weaker shears upstream of the sheaths and downstream in the ICME ejecta were also analyzed. In shears below the KH threshold, imbalance was approximately invariant or weakly rising with shear amplitude. Above the KH threshold, fluctuations tended toward a balanced state with increasing shear amplitude. Magnetic compressibility was also found to increase above the KH threshold. These findings are consistent with velocity shears being local sources of sunward fluctuations that act to reduce net imbalances in the antisunward direction, and suggest that the KH instability plays a role in this process.https://doi.org/10.3847/2041-8213/acc071Solar windInterplanetary turbulenceInterplanetary magnetic fieldsSolar coronal mass ejections |
| spellingShingle | Juska E. Soljento Simon W. Good Adnane Osmane Emilia K. J. Kilpua Imbalanced Turbulence Modified by Large-scale Velocity Shears in the Solar Wind The Astrophysical Journal Letters Solar wind Interplanetary turbulence Interplanetary magnetic fields Solar coronal mass ejections |
| title | Imbalanced Turbulence Modified by Large-scale Velocity Shears in the Solar Wind |
| title_full | Imbalanced Turbulence Modified by Large-scale Velocity Shears in the Solar Wind |
| title_fullStr | Imbalanced Turbulence Modified by Large-scale Velocity Shears in the Solar Wind |
| title_full_unstemmed | Imbalanced Turbulence Modified by Large-scale Velocity Shears in the Solar Wind |
| title_short | Imbalanced Turbulence Modified by Large-scale Velocity Shears in the Solar Wind |
| title_sort | imbalanced turbulence modified by large scale velocity shears in the solar wind |
| topic | Solar wind Interplanetary turbulence Interplanetary magnetic fields Solar coronal mass ejections |
| url | https://doi.org/10.3847/2041-8213/acc071 |
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