Magnetic patches in internetwork areas

Abstract

We present a study of internetwork magnetic elements that appear as bright points in G-band (photosphere) and Ca II H (low chromosphere) image sequences from the Dutch Open Telescope. Many bright points appear intermittently in groups of long-lived structures that we call “magnetic patches”. We develop an algorithm for the identification of bright points and magnetic patches. The average internetwork bright point lifetimes is measured to be 3.5 minutes in the G band, and 4.3 minutes in the Ca II H. We find an internetwork bright point number density of 0.02 Mm−2 in the G-band sequence and 0.05 Mm−2 in the Ca II H sequence. The bright points show a bimodal distribution of the frame-to-frame horizontal velocities, with a peak at 0 kms−1 and a wide hump centered around 1.2 kms−1. The patches last much longer than granular time scales (about nine hours) and outline cell-like structures on mesogranular scale. We conclude that transient internetwork bright points trace the locations of strong magnetic fields that exist before the bright point appears and remain after it disappears.