Solar Vortex Detection With Velocity Field Normalisation: Eliminating False Positives
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arXiv
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| Main Authors: | , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866915690074603520 |
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| author | McClure, Lauren Silva, Suzana Verth, Gary Ballai, Istvan Fedun, Viktor |
| author_facet | McClure, Lauren Silva, Suzana Verth, Gary Ballai, Istvan Fedun, Viktor |
| contents | Small-scale vortices in the solar photosphere play a central role in transporting mass, energy, and momentum into the upper solar atmosphere, yet reliably detecting these structures remains rather challenging. We address this problem by introducing a simple preprocessing step that normalises the velocity field by its magnitude. Our method preserves flow topology while suppressing shear-induced artefacts that lead to spurious detections in non-uniform, high-rotation environments. For validation, we apply this approach to high-resolution Bifrost simulations and evaluate vortex detection using four commonly employed methods: IVD, the $λ_2$-criterion, the Q-criterion, and the $Γ$ method. We assess which structures exhibit physically consistent rotation by using the $d$-criterion to automatically detect rotational plasma-flow features, which we use as an approximate ground truth. We find that, in the unnormalised field, a substantial fraction of detections made by the first three methods are false positive detections. Normalisation removes most of these. The $Γ$ method detects true vortices but misses a large number of vortical flows. The normalisation step yields better-defined and more realistic vortex boundaries. As the $Γ$ method underpins most observational analyses, current studies likely capture only a subset of vortical flows. By comparison, the other three methods detect four to five times more vortices after normalisation, suggesting that the true photospheric vortex coverage may be underestimated by a similar factor. Overall, this physically motivated preprocessing step enhances the accuracy and physical realism of vortex detection and offers a practical enhancement for analysing vortical flows in turbulent flows. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2512_18876 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Solar Vortex Detection With Velocity Field Normalisation: Eliminating False Positives McClure, Lauren Silva, Suzana Verth, Gary Ballai, Istvan Fedun, Viktor Solar and Stellar Astrophysics Small-scale vortices in the solar photosphere play a central role in transporting mass, energy, and momentum into the upper solar atmosphere, yet reliably detecting these structures remains rather challenging. We address this problem by introducing a simple preprocessing step that normalises the velocity field by its magnitude. Our method preserves flow topology while suppressing shear-induced artefacts that lead to spurious detections in non-uniform, high-rotation environments. For validation, we apply this approach to high-resolution Bifrost simulations and evaluate vortex detection using four commonly employed methods: IVD, the $λ_2$-criterion, the Q-criterion, and the $Γ$ method. We assess which structures exhibit physically consistent rotation by using the $d$-criterion to automatically detect rotational plasma-flow features, which we use as an approximate ground truth. We find that, in the unnormalised field, a substantial fraction of detections made by the first three methods are false positive detections. Normalisation removes most of these. The $Γ$ method detects true vortices but misses a large number of vortical flows. The normalisation step yields better-defined and more realistic vortex boundaries. As the $Γ$ method underpins most observational analyses, current studies likely capture only a subset of vortical flows. By comparison, the other three methods detect four to five times more vortices after normalisation, suggesting that the true photospheric vortex coverage may be underestimated by a similar factor. Overall, this physically motivated preprocessing step enhances the accuracy and physical realism of vortex detection and offers a practical enhancement for analysing vortical flows in turbulent flows. |
| title | Solar Vortex Detection With Velocity Field Normalisation: Eliminating False Positives |
| topic | Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2512.18876 |