The ionospheric signatures of reconnection are conditioned by the location of reconnection regions on the magnetopause, and by spatial and temporal variations in the associated reconnection electric field. These factors in turn depend on the underlying physics of reconnection. This talk will describe our work on using ionospheric signatures of reconnection, observed by SuperDARN radars, to distinguish between competing reconnection theories. This work is based on modelling results which provide a critical test for theories of magnetopause reconnection under certain seasonal and solar wind conditions. The implications of our results for the large-scale physics of reconnection will be discussed.