Photospheric flows measured with TRACE II. Network formation

Abstract

We analyse a 7 d (167 h) sequence of TRACE white-light images with 1″ angular resolution taken at 1 min cadence. The TRACE resolution and the fast cadence allows us to produce maps of the horizontal flow fields with high angular (1″) and temporal resolution (5 min). The field of view of 128″ × 128″ (≈ 93 Mm × 93 Mm) covers approximately an area of 10 to 30 supergranules. This area was followed during solar rotation. Magnetic flux was artificially inserted into the successive flow maps in the form of ephemeral regions with positive and negative polarity. The emergence rate of 2 × 1022 Mx h-1 with an average flux per region of about 1.1 × 1019 Mx produces a good reproduction of the chromospheric network as observed in images taken simultaneously at 1600 Å. In addition, we show that the quiet network can be maintained only if field elements of both polarities are inserted into the flow fields. Our analysis suggests that the network is fully replenished on a time scale of a day and the lifetimes of the magnetic elements are of a similar duration.