What is the Reynolds Number of the Solar Wind?
The Reynolds number, Re , is an important quantity for describing a turbulent flow. It tells us about the bandwidth over which energy can cascade from large scales to smaller ones, prior to the onset of dissipation. However, calculating it for nearly collisionless plasmas like the solar wind is chal...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2024-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ad118e |
| _version_ | 1797346834467782656 |
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| author | Daniel Wrench Tulasi N. Parashar Sean Oughton Kevin de Lange Marcus Frean |
| author_facet | Daniel Wrench Tulasi N. Parashar Sean Oughton Kevin de Lange Marcus Frean |
| author_sort | Daniel Wrench |
| collection | DOAJ |
| description | The Reynolds number, Re , is an important quantity for describing a turbulent flow. It tells us about the bandwidth over which energy can cascade from large scales to smaller ones, prior to the onset of dissipation. However, calculating it for nearly collisionless plasmas like the solar wind is challenging. Previous studies have used formulations of an “effective” Reynolds number, expressing Re as a function of the correlation scale and either the Taylor scale or a proxy for the dissipation scale. We find that the Taylor scale definition of the Reynolds number has a sizable prefactor of approximately 27, which has not been employed in previous works. Drawing from 18 years of data from the Wind spacecraft at 1 au, we calculate the magnetic Taylor scale directly and use both the ion inertial length and the magnetic spectrum break scale as approximations for the dissipation scale, yielding three distinct Re estimates for each 12 hr interval. Average values of Re range between 116,000 and 3,406,000 within the general distribution of past work. We also find considerable disagreement between the methods, with linear associations of between 0.38 and 0.72. Although the Taylor scale method is arguably more physically motivated, due to its dependence on the energy cascade rate, more theoretical work is needed in order to identify the most appropriate way of calculating effective Reynolds numbers for kinetic plasmas. As a summary of our observational analysis, we make available a data product of 28 years of 1 au solar wind and magnetospheric plasma measurements from Wind. |
| first_indexed | 2024-03-08T11:38:54Z |
| format | Article |
| id | doaj.art-de1096e908c24f4faa11686abd9521d0 |
| institution | Directory Open Access Journal |
| issn | 1538-4357 |
| language | English |
| last_indexed | 2024-03-08T11:38:54Z |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astrophysical Journal |
| spelling | doaj.art-de1096e908c24f4faa11686abd9521d02024-01-25T11:21:15ZengIOP PublishingThe Astrophysical Journal1538-43572024-01-01961218210.3847/1538-4357/ad118eWhat is the Reynolds Number of the Solar Wind?Daniel Wrench0https://orcid.org/0000-0002-7463-3818Tulasi N. Parashar1https://orcid.org/0000-0003-0602-8381Sean Oughton2https://orcid.org/0000-0002-2814-7288Kevin de Lange3Marcus Frean4https://orcid.org/0000-0001-5840-8760Victoria University of Wellington , Kelburn, Wellington 6012, New Zealand ; daniel.wrench@vuw.ac.nzVictoria University of Wellington , Kelburn, Wellington 6012, New Zealand ; daniel.wrench@vuw.ac.nzUniversity of Waikato , Hamilton 3240, New ZealandVictoria University of Wellington , Kelburn, Wellington 6012, New Zealand ; daniel.wrench@vuw.ac.nzVictoria University of Wellington , Kelburn, Wellington 6012, New Zealand ; daniel.wrench@vuw.ac.nzThe Reynolds number, Re , is an important quantity for describing a turbulent flow. It tells us about the bandwidth over which energy can cascade from large scales to smaller ones, prior to the onset of dissipation. However, calculating it for nearly collisionless plasmas like the solar wind is challenging. Previous studies have used formulations of an “effective” Reynolds number, expressing Re as a function of the correlation scale and either the Taylor scale or a proxy for the dissipation scale. We find that the Taylor scale definition of the Reynolds number has a sizable prefactor of approximately 27, which has not been employed in previous works. Drawing from 18 years of data from the Wind spacecraft at 1 au, we calculate the magnetic Taylor scale directly and use both the ion inertial length and the magnetic spectrum break scale as approximations for the dissipation scale, yielding three distinct Re estimates for each 12 hr interval. Average values of Re range between 116,000 and 3,406,000 within the general distribution of past work. We also find considerable disagreement between the methods, with linear associations of between 0.38 and 0.72. Although the Taylor scale method is arguably more physically motivated, due to its dependence on the energy cascade rate, more theoretical work is needed in order to identify the most appropriate way of calculating effective Reynolds numbers for kinetic plasmas. As a summary of our observational analysis, we make available a data product of 28 years of 1 au solar wind and magnetospheric plasma measurements from Wind.https://doi.org/10.3847/1538-4357/ad118eSolar windInterplanetary turbulenceMagnetohydrodynamicsSpace plasmas |
| spellingShingle | Daniel Wrench Tulasi N. Parashar Sean Oughton Kevin de Lange Marcus Frean What is the Reynolds Number of the Solar Wind? The Astrophysical Journal Solar wind Interplanetary turbulence Magnetohydrodynamics Space plasmas |
| title | What is the Reynolds Number of the Solar Wind? |
| title_full | What is the Reynolds Number of the Solar Wind? |
| title_fullStr | What is the Reynolds Number of the Solar Wind? |
| title_full_unstemmed | What is the Reynolds Number of the Solar Wind? |
| title_short | What is the Reynolds Number of the Solar Wind? |
| title_sort | what is the reynolds number of the solar wind |
| topic | Solar wind Interplanetary turbulence Magnetohydrodynamics Space plasmas |
| url | https://doi.org/10.3847/1538-4357/ad118e |
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