Objective Lagrangian Vortex Detection in the Solar Photosphere

Vortices in the solar photosphere can be linked to a wide range of events, such as small-scale solar eruptions, wave excitation, and heating of the upper part of the solar atmosphere. Despite their importance in solar physics, most of the current studies on photospheric vortices are based on methods...

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Bibliographic Details
Published in:Astrophysical journal. Letters 2018-08, Vol.863 (1), p.L2
Main Authors: Silva, Suzana de Souza e Almeida, Rempel, Erico Luiz, Gomes, Tiago Francisco Pinheiro, Requerey, Iker S., Chian, Abrahamm C.-L.
Format: Article
Language:English
Subjects:
Compressible flow
convection
Criteria
Fluid dynamics
Identification methods
Invariants
methods: data analysis
Photosphere
Satellite data
Solar atmosphere
Solar physics
Streamlines
Sun: granulation
Sun: photosphere
Time dependence
Translations
Velocity distribution
Vortices
Vorticity
Wave excitation
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Summary:Vortices in the solar photosphere can be linked to a wide range of events, such as small-scale solar eruptions, wave excitation, and heating of the upper part of the solar atmosphere. Despite their importance in solar physics, most of the current studies on photospheric vortices are based on methods that are not invariant under time-dependent translations and rotations of the reference frame and are Eulerian; i.e., they are based on single snapshots of a velocity field and, therefore, do not convey information on the true long-term motion of fluid particles on a time-varying field. Another issue with methods for vortex detection is that typically they provide false identifications in highly compressible flows. This Letter presents a novel criterion that effectively removes wrong detections based on the geometry of the streamlines of the displacement vector of fluid elements and can be readily applied to other astrophysical flows. The new criterion is applied to the Lagrangian-averaged vorticity deviation (LAVD), which is a recently developed frame invariant vortex detection method. The advantage of LAVD is that it delimits the vortices' outer boundaries precisely by following up the trajectories of fluid elements in space and time. The proposed method is compared with two other techniques using horizontal velocity fields extracted from Hinode satellite data.
ISSN:2041-8205
2041-8213
DOI:10.3847/2041-8213/aad180