The patchy and intermittent nature of the solar wind-magnetosphere interaction suggests that MHD mesoscale processes are important in the description of transport at the magnetopause. In order to deal with the nonlinear electromagnetic interaction of localized fluctuations in a highly imhomogeneous region such as the magnetopause, a quasi-particle description involving compressional and shear Alfv¿nons is introduced to give the particle-like behavior of the corresponding MHD waves. The driven nature of the solar wind-magnetosphere interaction, and in particular driven reconnection, is discussed in terms of the interactions between these Alfv¿nons, and between Alfv¿nons and the ambient magnetic field. The dependence of the threshold conditions for the onset of the driven reconnection on the IMF and the dynamic pressure of the solar wind is calculated by analyzing the generation and interaction of the Alfv¿nons. The conversion of compressional Alfv¿nons gives a mechanism for the direct generation of field-aligned current filaments. ¿ American Geophysical Union 1994