The Reliability of Local Correlation Tracking for Inferring Photospheric Intensity Vortices

Abstract Magnetoconvective simulations of the solar photosphere show ubiquitous formation of vortices in intergranular lanes, which are thought to contribute to the energy transfer between atmospheric layers. Observationally, these vortices are often reported as photospheric intensity vortices, with their flow field assumed parallel to the plane of sky, making their identification a challenge. The most common method to detect these vortices is to infer the photospheric velocity field using Fourier local correlation tracking (FLCT) and identifying vortical motions within. To validate FLCT as a tool for inferring photospheric intensity vortex flows, FLCT was performed on TiO 705.8 nm observations from the Visible Broadband Imager at the Daniel K. Inouye Solar Telescope, as well as on synthetic intensity images derived from the MURaM code. Using Γ-functions on velocity vectors, vortices were identified while characterizing their statistical properties. Vortices in MURaM FLCT velocity fields were then compared with those in the MURaM-simulated velocity field. It was found that the FLCT kernel size has a significant impact on recovered vortex properties and quantity. However, statistical distributions of the properties of vortex lifetimes and areas remain similar. Furthermore, vortices in the MURaM-simulated velocity field were found to be much smaller than those in MURaM FLCT-derived velocity fields, with their overlap in space being 0.4%–19.7%, depending on the FLCT kernel size. The vast majority of those that do match are coincidental and arise from particularly large choices of kernel size. Therefore, FLCT was determined to be unreliable for inferring photospheric intensity vortices in intergranular lanes.