Flux pile-up magnetic reconnection in the solar photosphere

Magnetic reconnection in the temperature minimum region of the solar photosphere, observationally manifested as canceling magnetic features, is considered. Flux pile-up reconnection in the Sweet-Parker current sheet is analyzed. It is shown that the standard Sweet-Parker reconnection rate in the photosphere is too slow to explain the observed cancellation. Flux pile-up reconnection scalings, however, are shown to be in agreement with the speeds of canceling magnetic fragments, magnetic fields in the fragments, and the rates of magnetic flux cancellation, derived from SOHO MDI data. Pile-up factors in the range between 1 and 5 and local reconnecting magnetic fields of a few hundred G are calculated for the analyzed canceling features. The analysis shows that flux pile- up is a likely mechanism for adjusting the local parameters of reconnecting current sheets in the photosphere and for sustaining the reconnection rates that are determined by large-scale supergranular flows. The upward mass flux in the reconnection jet, associated with a large canceling feature, is predicted to exceed 10(15) g hr(-1). Hence, cancellation in a few photospheric patches over several hours can lead to the formation of a solar filament in the corona.