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

Reconnection at the dayside magnetopause is the principal method by which e nergy 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 a ssuming that reconnection occurring in regions where the magnetosheath flow is super-Alfvenic must be transient. We use a simple magnetospheric model to illustrate where on the magnetopause transient reconnection is most like ly to occur, and show that the location of these regions is dependent criti cally upon the dipole tilt angle and the interplanetary magnetic field orie ntation. 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. Fo r example, the results suggest that reconnection for northward IMF is almos t always likely to be transient.