(a) Initial magnetic field distribution when the bipoles are inserted over a finite region at both the photosphere and corona. The trailing bipole is given a twist of ﹩\beta =-0.3﹩ and the lead bipole, ﹩\beta =-0.2﹩. (b) Resulting magnetic structure after the bipoles have expanded to fill the comutational domain and cross‐connections have been made. (c) Selection of field lines in a two‐dimensional cut through the center of the bipoles.