Coronal flux recycling times

High-cadence, high-resolution magnetograms have shown that the quiet-Sun photosphere is very dynamic in nature. It is comprised of discrete magnetic fragments which are characterized by four key processes - emergence, coalescence, fragmentation and cancellation. All of this will have consequences for the magnetic field in the corona above.

The aim of this study is to gauge the effect of the behavior of the photospheric flux fragments on the quiet-Sun corona. By considering a sequence of observed magnetograms, photospheric flux fragments are represented by a series of point Sources and the resulting potential field arising from them is examined. It is found that the quiet-Sun coronal flux is generally recycled on time scales considerably shorter than the corresponding time scales for the recycling of photospheric flux. From the motions of photospheric fragments alone, a recycling time of coronal flux of around 3 h is found. However, it is found that the amount of reconnection driven by the motions of fragments is comparable to the amount driven by emergence and cancellation of flux, resulting in a net flux replacement time for the corona of only 1.4 h.

The technique used in this study was briefly presented in a short research letter (R. M. Close et al., Astrophys. J., 612, L81, 2004) here the technique is discussed in far greater depth. Furthermore, an estimate is made of the currents required to flow along separator field lines in order to sustain the observed heating rates (assuming separator reconnection is the key mechanism by which the solar corona is heated).