This paper deals with dynamic processes caused by irregularities close to the magnetopause as discussed by several authors in the recent literature. The problem of plasma entry is tackled theoretically by assuming individual filaments appearing at the magnetopause with an excess inward momentum. The conditions under which entry is possible are derived in a two dimensional model. With ideal MHD, entry is essentially confined to the cases of near magnetic field alignment. The consequences of nonideal MHD processes are discussed qualitatively. The results support the possibility of the presence of an irregular distribution of 'merging patches' on the magnetopause, giving better agreement with recent observations than the classical steady state reconnection picture. all entry mechanisms discussed are potential candidates for the processes that form the plasma boundary layer.