Measurements of Solar Magnetic Element Motion from High-resolution Filtergrams

Solar photospheric ÑowÐeld properties on scales are measured using local correlation tracking sub-0A.5 (LCT) and object tracking of magnetic bright points (MBPs : photospheric bright points associated with magnetic elements). The dataset is a 70 minute time series of cospatial and cotemporal G-band 4305 Ó and wideband 4686 Ðltergrams obtained with the 50 cm Swedish Vacuum Solar Telescope on the Ó island of La Palma, Spain. We examine a 29A ] 70A Ðeld of view (FOV) near disk center and compare a 29A ] 29A magnetic network subÐeld and a 27A ] 27A apparently nonmagnetic ““ quiet-Sun ÏÏ subÐeld. 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 or less in all frames D0A.4 of the restored data set. From LCT on a grid with FWHM apodization, we Ðnd the Ñow speeds to be Rayleigh dis0A.4 0A.83 tributed 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 region ÏÏ deÐned 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 Ñow structures are smaller and much more chaotic. Mesogranulation is entirely absent in the magnetic 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. Subject headings : Sun: magnetic Ðelds È Sun: faculae, plages È Sun: photosphere È techniques : image processing