Some comments on transient and steady-state reconnection at the dayside magnetopause

Reconnection at the dayside magnetopause is the principal method by which energy is transferred from the solar wind into the magnetosphere-ionosphere system. There is still considerable uncertainty as to whether reconnection is transient or quasi-steady. Here we discuss some of the implications of assuming that reconnection occurring in regions where the magnetosheath flow is super-Alfvénic must be transient. We use a simple magnetospheric model to illustrate where on the magnetopause transient reconnection is most likely to occur, and show that the location of these regions is dependent critically upon the dipole tilt angle and the interplanetary magnetic field orientation. Although our idealised examples do not take into account temporal variations of the solar wind conditions, or the influence of the bow shock or magnetosheath, we believe that they demonstrate interesting features. For example, the results suggest that reconnection for northward IMF is almost always likely to be transient.