Measurements of Solar Magnetic Element Motion from High‐Resolution Filtergrams

Abstract

Solar photospheric flowfield properties on sub-05 scales are measured using local correlation tracking (LCT) and object tracking of bright points (MBPs: photospheric bright points associated with elements). The dataset is a 70 minute time series of cospatial and cotemporal G-band 4305 A and wideband 4686 A filtergrams obtained with the 50 cm Swedish Vacuum Solar Telescope on the island of La Palma, Spain. We examine a 29'' × 70'' field of view (FOV) near disk center and compare a 29'' × 29'' network subfield and a 27'' × 27'' apparently nonmagnetic quiet-Sun subfield. The mean time between frames is 23.75 s. Each frame is created by partitioned phase-diverse speckle restoration of three image pairs acquired rapidly in sequence. Angular resolution is ~04 or less in all frames of the restored data set. From LCT on a 04 grid with 083 FWHM apodization, we find the flow speeds to be Rayleigh distributed with a mode of 550 m s-1 and an average of 950 m s-1 in the network FOV; in the quiet FOV the modal speed is 700 m s-1 with a mean of 1100 m s-1. Within the network FOV, a magnetic defined by the loci of tracked MBPs exhibit even greater alteration: rms contrast of the region is 8% higher in the G band compared to areas outside, LCT speeds are reduced by a factor of 1.6, and the convective flow structures are smaller and much more chaotic. Mesogranulation is entirely absent in the region. The modal and mean speeds of 534 tracked MBPs are 300 m s-1 and 1470 m s-1, respectively. MBPs split and merge with mean times of 320 and 404 s respectively. The mean lifetime of MBPs in the data set is 9.33 minutes although approximately 5% of the objects can be tracked for the entire 70 minute duration of the time series.