Large-scale Vortices in the Solar Photosphere: Statistical Properties and the Reliability of Local Correlation Tracking

Abstract

Vortices are observed throughout the solar atmosphere, spanning a wide range of spatial scales. Although small-scale vortices have been studied extensively, mesoscale vortices remain less explored, and it is still unclear whether they can be reliably recovered from observations. Mesogranular-scale motions are recovered from the R2D2 simulations by applying Gaussian spatial smoothing to the horizontal velocity field with full width at half maximum (FWHM) values of 2.5-4.0 Mm. To evaluate the accuracy of local correlation tracking (LCT) and its suitability for identifying mesogranular vortices, we apply LCT to synthetic intensity maps at $τ= 1$ using the same spatial windows and temporal averaging windows of 10-60 minutes. Vortices are identified in both the reference and LCT-derived velocity fields using the $Γ$ method. For all tested parameter combinations, LCT underestimates the number of mesogranular-scale vortices. The best overall recovery is obtained for relatively small spatial smoothing scales (FWHM $\leq 3.5$ Mm) and short averaging windows ($\leq 20$ minutes), which provide the most reliable vorticity and lifetime statistics while maintaining strong agreement in vortex radius and area distributions. Our analysis shows that only a modest fraction of LCT-detected vortices correspond to vortices identified in the reference velocity field (3.54%-17.88%), depending on FWHM and temporal averaging. This indicates that vortex-driven dynamics inferred from LCT-detected vortices should be interpreted with caution. Our results suggest that applying the $Γ$ method to LCT-derived velocity fields can recover useful statistical properties of mesoscale vortical structures, especially their temporal trends and characteristic sizes.