Topological aspects of global magnetic field reversal in the solar corona

Every eleven years on average, the dipolar component of the Sun's global coronal magnetic field reverses in sign - a consequence of the sunspot cycle. In this paper we begin to investigate the complex changes in coronal structure during the reversal. We present a simplified model of the solar cycle containing six time-varying photospheric sources of magnetic field and analyse the evolution of the global coronal field using the technique of magnetic charge topology. Surprisingly, a sequence of seventeen topological changes takes place in the model between one solar minimum state and the next; many of the resultant topological configurations correspond to observable magnetic field structures in the real corona. We also show how descriptions of all the six-source topological states from the model can be built up in terms of combinations of simpler four-source states, providing a framework for future descriptions of even more complicated topological states.